Postprandially, amino acids and di/tripeptides are thought to be primarily absorbed in the proximal small intestine. However, there have been no in vivo demonstrations of regional differences in amino acid transport dynamics between the proximal and distal small intestines. We monitored plasma amino acid responses in the jejunal and ileal mesenteric veins of rats after oral administration of a diet or an amino acid mixture (Expt 1) and in the portal vein after direct administration of the amino acid mixture into the lumen of the jejunum or ileum (Expt 2). In Expt 1, the total and some amino acid concentrations in the jejunal mesenteric vein were slightly higher than those in the ileal mesenteric vein after oral administration of the amino acid mixture, suggesting that the ileum actively transports luminal amino acids to the basolateral side, comparable to the jejunum. In Expt 2, portal amino acid concentrations were elevated to a greater extent after direct administration of the amino acid mixture into the ileal lumen than into the jejunal lumen. These results demonstrate regional differences in amino acid transport dynamics in vivo and suggest that the ileum has a higher capacity for transporting amino acids than the jejunum. Our findings highlight the importance of the ileum in postprandial amino acid absorption and metabolism.

Freezing damage is a major limiting factor to Pistachio cultivation in cold climates. Assessment of pistachio genotypes to freezing stress is important for the selection of tolerance cultivars in these regions. In this study, nine genotypes belong to six Pistacia species (P. terebinthus L., P. atlantica Desf., P. atlantica subsp. kurdica P. atlantica subsp. mutica, P. khinjuk Stocks., P. vera var. Sarakhs, P. vera cv. Badami-Riz-Zarand I, P. vera cv. Badami-Riz-Zarand II) and an interspecies hybrid named UCB1 (P. atlantica × P. integrrima) were evaluated to freezing stress at temperatures of −4, −8, −12 and, −16°C in the months of December, January and February. Results showed that electrolyte leakage (EL) percentage and means of eco-physiological parameters varied among genotypes with the highest soluble carbohydrates and phenolic compounds observed in species of P. atlantica subsp. kurdica and P. vera var. Sarakhs respectively. In February, the highest calcium and potassium concentrations of shoot were observed in P. terebinths and P. vera var. Sarakhs genotypes respectively. The highest EL percentage was observed at −16°C in P. atlantica and P. khinjuk and the lowest in P. terebinthus and P. vera var. Sarakhs.

The current study aimed to investigate biofortification of maize grown under different irrigation intervals, i.e. 15, 20 and 25 days (hereinafter referred to as IR15, IR20 and IR25, respectively), using foliar application treatments (silicon (Si), zinc (Zn), silver nanoparticles (AgNPs), Si + Zn, Si + AgNPs, Zn + AgNPs and Si + Zn + AgNPs) in two growing seasons, 2020 and 2021. A split-plot design with four replications was used, where irrigation intervals and foliar treatments were assigned in main plots and subplots, respectively. IR15 received a total of 7925 m3/ha irrigation water divided over seven irrigations, while IR20 received 5690 m3/ha divided over five irrigations and IR25 received 4564 m3/ha divided over four irrigations. The highest yield and grain quality were observed in plants irrigated at 15-day intervals. Spraying the canopy with Si, Zn and AgNPs, either individually or in combination, reduced the negative impact of water stress caused by longer irrigation intervals on plant growth, yield, yield components and grain protein content. In IR15 + AgNPs + Zn, most of the studied parameters, except for proline content, showed a high positive impact, especially on 100-kernel weight (KW). In contrast, IR25 + Si + AgNPs + Zn showed the highest positive effects on proline and protein contents but a negative impact on the harvest index. Collectively, IR15 + Si + AgNPs + Zn resulted in the highest values of all studied parameters, followed by IR15 + Si + AgNPs and IR15 + Si + Zn. In conclusion, our results suggest that an irrigation interval of 15 days combined with application of Si, Zn and AgNPs has the potential to improve yield and quality of maize under water deficit stress.

One of the challenges to improve sweet corn [Zea mays var. Saccharata (Sturtev.) L. H. Bailey] production is finding a way to increase crop establishment and decrease weed infestation. Crop establishment and weed control are of prime importance in sweet corn production. Three methods of seedbed preparation including pre-planting irrigation before ridge-furrow preparation, pre-planting irrigation after ridge-furrow preparation and irrigation after planting, and four wheat (Triticum aestivum L.) residue rates (0, 250, 500 and 750 g/m2) were arranged in a split plot based on a randomized complete blocks design. Higher seedling emergence and weed control were significantly obtained in pre-planting irrigation than irrigation after planting treatments. Wheat residue mulching reduced soil moisture depletion, proline and soluble carbohydrates contents with decreasing weed biomass. The efficiency of weed management was found to be ensured using pre-planting irrigation coupled with wheat residues application. The grain yield was the highest (1433 g/m2) using pre-planting irrigation and wheat residue mulching (750 g/m2). Weed biomass decreased by 58% in pre-planting irrigation after ridge-furrow preparation and wheat residue mulching (750 g/m2) compared to irrigation after planting and no-mulching treatment. Therefore, pre-planting irrigation after ridge-furrow preparation and wheat residues application (500–750 g/m2) were optimal management practices for crop establishment and weed control to improve yields and water productivity of sweet corn in the region.

To evaluate the responses of some important agronomic traits of 14 bread wheat cultivars, a split plot experiment was conducted based on a randomized complete block design under non-stress, moderate and severe salinity stress conditions. In this study, Backcross and Roshan were identified as the most salinity-tolerant cultivars, while Mihan and Shirudi were considered as the most salinity-sensitive cultivars. The proline content, as well as Δ1-pyrroline-5-carboxylate synthase (P5CS) and vacuolar-type H+-ATPase subunit E (W36) gene expression levels, were examined in these cultivars under normal, moderate and high salinity stress conditions. The proline content and P5CS gene expression level increased with a rise in NaCl concentration. Further, a direct relationship was observed between the proline content and P5CS gene expression in all samples. Our results showed that W36 gene expression in Backcross and Roshan cultivars, as the most resistant ones, strongly increased with elevation of the NaCl concentrations. On the other hand, in the sensitive cultivars such as Mihan and Shirudi, small changes were observed in the gene expression levels with rising salinity levels. Additionally, Backcross and Roshan cultivars had the highest proline content as well as P5CS and W36 genes expression levels under moderate and high salinity stress levels.

The only generally accepted treatment of coeliac disease (CD) is a lifelong gluten-free diet. Wheat gluten proteins include gliadins, low and high molecular weight glutenins. However, we have found significant structural variations within these protein families among different cultivars. To determine which structural motifs might be less toxic than others, we assessed five variants of α-gliadin immunodominant CD-toxic peptides synthesised as 16mers in CD T cell stimulation assays with gluten-sensitive T cell lines generated from duodenal biopsies from CD-affected individuals. The peptides harboured the overlapping T cell epitopes DQ 2.5-glia-α-2 and naturally occurring variants that differed in certain amino acids (AA). The results revealed that introduction of two selected AA substitutions in α-gliadin peptides reduced immunogenicity. A peptide with three AA substitutions involving two glutamic acids (E) and one glutamine residue (G) revealed the peptide was negative in 5:5 samples. We used CD small-intestinal organ culture to assess CD toxicity that revealed two peptides with selected substitution of both glutamic acid (E) and proline (P) residues abrogated evidence of CD toxicity.

Porcine circovirus type 2 (PCV2) is associated with various diseases that impose a significant economic burden on the swine industry. We hypothesised that nutritional supplementation with proline to enhance the immune response might be a useful prophylactic measure against PCV2 infection. To test this hypothesis, in the present study, we measured clinical data, including blood parameters, serum cytokine profile, PCV2 virus load in organs and serum, and microscopic lesions in the lung, liver and spleen, in both PCV2-infected pregnant and non-pregnant mice. Dietary supplementation with proline had no effect (P>0·05) on abortion rates in PCV2-infected pregnant mice, although a numerically lower abortion rate (22·2 v. 44·4 %) was observed compared with the control. Dietary supplementation with proline significantly increased serum C-reactive protein levels (P= 0·03) in PCV2-infected pregnant mice, and increased serum TNF-α levels (P= 0·01), leucocytes (P< 0·05), lymphocytes (P< 0·05) and neutrophilic granulocytes (P< 0·05) in PCV2-infected non-pregnant mice. Meanwhile, dietary proline significantly (P< 0·05) decreased the PCV2 virus load in the lung. Furthermore, mice in the dietary proline group showed a significant (P< 0·01) decrease in microscopic lesion scores in the lung, liver and spleen compared with those in the alanine group. Collectively, dietary proline supplementation confers a functional role in PCV2-infected mice.

Amino acids often cocrystallize with water molecules, which make them pseudopolymorphs of their anhydrous forms. In this work, we discuss in detail the hydrogen bond patterns in anhydrous L-proline and DL-proline and its pseudopolymorphic forms: L-proline monohydrate and DL-proline monohydrate. For this propose, the crystal structure of L-proline anhydrous was determined from synchrotron X-ray powder diffraction data and refined using the Rietveld method. Special emphasis is given to the role played by the water molecule in the hydrogen bond network observed in the crystalline structures.

Introduction. Au Maroc, les agrumes sont confrontés à une combinaison de stress biotiques [virus de la tristeza (CTV) / Phytophthora] et abiotiques (salinité, alcalinité et sécheresse). La plupart de ces contraintes doivent être gérées individuellement par le choix d’un porte-greffe adapté. Cependant, la propagation de la CTV dans le bassin méditerranéen va bientôt interdire l’utilisation du bigaradier, porte-greffe traditionnel, qui offre actuellement une tolérance suffisante à la salinité et l’alcalinité. Par conséquent, la sélection de nouveaux porte-greffes d’agrumes devient pressante. Notre étude a cherché à étudier l’effet de différents régimes hydriques sur la croissance de dix porte-greffes d’agrumes : citrange Carrizo (France), citrange Carrizo (Maroc), citrange Troyer, citrange Yuma, Citrus volkameriana; deux Poncirus trifoliata d’origine différente, citrumelo, Mand. Sunki  ×  Poncirus trifoliata, et Poorman. Matériel et méthodes. Pour chaque porte-greffe, des plants âgés de trois mois ont été cultivés en pots de plastique (0,5 L) dans une serre à El Menzeh, INRA, Maroc; ils ont été soumis à trois régimes hydriques [(100 %, 75 % et 50 %) d’humidité à la capacité au champ (Hcc) du substrat]. L’expérimentation a été disposée en un split-plot à trois traitements. Les paramètres morphologiques mesurés ont été la hauteur de la plante et l’accumulation de matière sèche et fraîche. Les paramètres physiologiques étudiés ont été la teneur relative en eau, le taux de transpiration et les teneurs en chlorophylle, sucres solubles et proline. Résultats. Les paramètres morphologiques et physiologiques ont été affectés par l’intensité du stress hydrique appliqué. Cependant, les porte-greffes se sont comportés différemment vis-à-vis de cette contrainte. Le stress hydrique a induit une augmentation de la teneur en proline et en sucres solubles au niveau des feuilles des porte-greffes. Conclusion. Le stress hydrique affecte d’une manière significative les caractéristiques physiologiques et morphologiques des porte-greffes d’agrumes et, en conditions de déficit hydrique extrême (50 % Hcc), un comportement différentiel des porte-greffes a été constaté. Sur la base des résultats que nous avons obtenus, ce sont les porte-greffes citrange Carrizo (Maroc) et Poorman qui présenteraient globalement les meilleures aptitudes à résister aux conditions de stress hydrique.

Introduction. Drought stress is the major factor affecting growth, development and production of walnut trees. In Iran, approximately 33 Mha of land is affected by salinization and drought stress. Finding genetic resources tolerant to drought stress at different growth stages is important for such semi-arid regions. Our aim was to understand better the adaptive mechanisms that enable different genotypes of walnut population to survive under drought stress, and to provide some useful clues for walnut tree breeding toward improved drought tolerance with utilization of existing drought-tolerant genetic resources. Materials and methods. To study the mechanism(s) involved in drought tolerance of some Persian walnut genotypes, drought stress was induced using polyethylene glycol-6000 to produce water potentials of 0 Mpa (control), –0.10 MPa, –0.50 MPa, –0.75 MPa, –1.00 MPa, –1.50 MPa and –2.00 MPa. The amount of proline and soluble sugar accumulation in four walnut genotypes (‘Panegine20’, ‘Lara’, ‘Serr’ and ‘Chandler’) were determined after being exposed to the various water potential levels. Results. The rates of seed germination in all genotypes were significantly reduced by low external water potentials. Plants exposed to water stress had a higher amount of soluble sugars in roots and shoots of tolerant genotypes (‘Panegine20’ and ‘Chandler’) and a lower amount of starch in their tissues. These results imply the important roles of soluble sugars as solutes conferring resistance to drought in these genotypes. The free proline levels were also increased in response to drought stress. They were higher in drought-tolerant genotypes than in sensitive ones (‘Lara’ and ‘Serr’). Proline increased more in shoots than in roots. However, the soluble sugar and starch fluctuations were higher in the roots. Conclusion. Our results support a direct correlation between the degree of drought stress and proline content. As a consequence, proline concentrations could be used as a biochemical marker of drought stress level in walnut plants.

The aim of this work was to analyse the capacity for protein synthesis in embryonic axes from long-term-stored maize seeds, including the role of proline. Embryonic axes from seeds stored for 13 years (S) and non-stored seeds (NS) were incubated in nutrient media after application of [14C]proline. Transformation of [14C]proline into other amino acids was analysed by thin-layer chromatography. After 6 h of incubation, no other labelled amino acids were found. Incorporation of 14C into total soluble and cell-wall (proline-rich) proteins was assessed during this period. Incorporation of [14C]proline into specific cell-wall proteins was lower in S than in NS axes.

Studies using [35S]methionine showed that protein synthesis was slower in axes of S than in NS seeds. Analyses of these proteins by gel electrophoresis and fluorography revealed qualitative differences between the [35S]methionine proteins synthesized by both types of axes. The NS: S ratios for the [35S]proteins were larger than those from the [14C]proline assays. These data may be interpreted as an indication of differential deterioration of transcription or translation in the axes during long-term seed storage.

Introduction. La salinité du sol et de l'eau d'irrigation, aggravée par la rareté des précipitations, est une menace permanente pour la culture des agrumes au Maroc. Le choix d'un porte-greffe tolérant à ce stress abiotique serait un moyen efficace pour pallier ce problème. L'expérimentation présentée a permis d'évaluer, vis-à-vis du stress salin, trois porte-greffes récemment introduits au Maroc. Matériel et méthodes. Des plants de citrange Carrizo et de deux hybrides, H1 et H2, issus du croisement Poncirus trifoliata × Citrus sunki Hort. ex Tan. ont été évalués pour leur tolérance à la salinité. Les plants âgés de 18 mois ont été irrigués par une solution nutritive additionnée de (25, 35, et 70) mM de NaCl durant un ou deux mois alors que les plants témoins recevaient la solution nutritive sans NaCl. Après traitement, les teneurs en proline et en sucres solubles ont été mesurées dans les feuilles des porte-greffes traités. Résultats. L'accumulation de proline a été indépendante de la présence de NaCl dans la solution d'irrigation mais elle a varié en fonction du porte-greffe. En revanche, NaCl a fortement stimulé l'accumulation des sucres solubles chez les trois porte-greffes et cette accumulation a été très importante chez le porte-greffe H1. Discussion et conclusions. Ces résultats concordent en partie avec certains des travaux déjà publiés. Dans nos conditions expérimentales, l'effet des concentrations salines utilisées a pu être compensé par l'accumulation de sucres solubles dans les feuilles, notamment dans celles du porte-greffe H1. Celui-ci ayant montré moins de toxicité foliaire que les deux autres porte-greffes, l'accumulation de sucres solubles dans la feuille d'agrumes pourrait être un indice de tolérance à la salinité.

Strabismus induces an abnormal pattern of alternating light and dark columns of cytochrome oxidase (CO) activity in macaque striate cortex. This pattern may arise because visual perception is suppressed in one eye to avoid diplopia. To test whether CO activity is reduced in the ocular dominance columns of the suppressed eye, we performed monocular enucleation to co-label the ocular dominance columns with Zif268 immunohistochemistry in seven exotropic adult Macaca fascicularis. This approach was unsuccessful, for two reasons. First, Zif268 yielded inconsistent labelling, that was usually greater in the enucleated eye's ocular dominance columns, but was sometimes greater in the intact eye's columns. Therefore, Zif268 was not a reliable method for identifying the ocular dominance columns serving each eye. Second, in three control animals we found that a brief survival period following monocular enucleation (needed for Zif268 levels to change) was long enough to alter CO staining. For example, a survival time of only 3 h was sufficient to induce CO columns, indicating that the activity of this enzyme fluctuates more rapidly than realized previously. Independent of these findings, we have also discovered that acute monocular enucleation produces a vivid pattern of ocular dominance columns visible in unstained or CO-stained sections under dark-field illumination. The ocular dominance columns of the acutely enucleated eye appear dark. This was verified by labelling the ocular dominance columns with [3H]proline. Dark-field illumination of the cortex after acute monocular enucleation offers a new, easy method for identifying the ocular dominance columns in macaques.

Osmotic adjustment (OA) and increased cell-wall extensibility required for expansive leaf growth are well defined components of adaptation to water stress in dry soil, which might interact with soil phosphorus (P) concentration and defoliation frequency for intensively grazed white clover in legume-based pastures. Experiments were conducted with frequently and infrequently defoliated mini-swards of white clover growing in dry soil with low and high P concentrations. The higher yielding high-P plants were able to dry the soil to greater soil water suctions; their leaves had lower water potential values, yet they showed fewer water stress symptoms and underwent a more complete recovery from the water stress symptoms on rewatering, than the low-P plants. High- P plants had greater OA, proline concentration and leaf expansion rate. On the other hand, low-P plants showed an increased osmotic concentration when there was no change in the total solute content per unit of leaf d. wt, indicating more loss of water from the leaf tissue. The key measures that appeared to be directly associated with plant recovery over a short period following water stress were increased proline concentration and leaf expansion rate, probably resulting from increased cell-wall extensibility rather than increased production of cells for the high-P plants.

Parameters of convective ventilation and also the content and composition of free amino acids and free carbohydrates in roots, basal culm internodes and leaves were investigated in five stands of Phragmites australis that were subjected to different growth conditions and salinity levels. Shoot length, stem diameter and productivity decreased with increasing salinity. These morphometric variations in turn affected parameters of convective ventilation and amino acid patterns. Phragmites populations growing at the highest salinity levels possessed the lowest rhizome conductivities, which was probably caused by their more pronounced xeromorphic growth. High counterpressures of the rhizome system and low stem diameters were limiting factors for convective flows. The Phragmites stand with lowest flow rate and ventilation efficiency had the highest percentage of alanine, serine and γ-aminobutyric acid (55% of total free amino acids) in its roots, indicating hypoxic stress in basal plant parts. Increasing salinity was connected with significantly higher fractions of glutamine (in basal culm internodes), glutamate (in roots) and proline (in both) as well as slightly increasing osmolality of plant sap. However, total contents of free amino acids and carbohydrates were low, and not related to either salinity level or osmolality of plant sap. This suggests that they might not have an important, direct role as an osmolyte in P. australis. Stand-specific variations in amino acid and carbohydrate patterns of leaves were negligible. Ratios of amino acids to carbohydrate were positively related to potential N supply. It is concluded that (1) salinity affects convective rhizome ventilation by varying the reed morphometry, and (2) the pattern of free amino acids responds characteristically to conditions of salinity and hypoxic growth.

The in vitro refolding of hen egg-white lysozyme is studied in the presence of various osmolytes. Proline is found to prevent aggregation during protein refolding. However, other osmolytes used in this study fail to exhibit a similar property. Experimental evidence suggests that proline inhibits protein aggregation by binding to folding intermediate(s) and trapping the folding intermediate(s) into enzymatically inactive, “aggregation-insensitive” state(s). However, elimination of proline from the refolded protein mixture results in significant recovery of the bacteriolytic activity. At higher concentrations (>1.5 M), proline is shown to form loose, higher-order molecular aggregate(s). The supramolecular assembly of proline is found to possess an amphipathic character. Formation of higher-order aggregates is believed to be crucial for proline to function as a protein folding aid. In addition to its role in osmoregulation under water stress conditions, the results of this study hint at the possibility of proline behaving as a protein folding chaperone.

We describe a novel N-terminal α-helix local motif that involves three hydrophobic residues and a Pro residue (Pro-box motif ). Database analysis shows that when Pro is the N-cap of an α-helix the distribution of amino acids in adjacent positions changes dramatically with respect to the average distribution in an α-helix, but not when Pro is at position N1. N-cap Pro residues are usually associated to Ile and Leu, at position N′, Val at position N3 and a hydrophobic residue (h) at position N4. The side chain of the N-cap Pro packs against Val, while the hydrophobic residues at positions N′ and N4 make favorable interactions. To analyze the role of this putative motif (sequence fingerprint hPXXhh), we have synthesized a series of peptides and analyzed them by circular dichroism (CD) and NMR. We find that this motif is formed in peptides, and that the accompanying hydrophobic interactions contribute up to 1.2 kcal/mol to helix stability. The fact that some of the residues in this fingerprint are not good N-cap and helix formers results in a small overall stabilization of the α-helix with respect to other peptides having Gly as the N-cap and Ala at N3 and N4. This suggests that the Pro-box motif will not specially contribute to protein stability but to the specificity of its fold. In fact, 80% of the sequences that contain the fingerprint sequence in the protein database are adopting the described structural motif, and in none of them is the helix extended to place Pro at the more favorable N1 position.

Conformational free energy calculations have been carried out for proline-containing alanine-based pentadecapeptides with the sequence Ac-(Ala)n-Pro-(Ala)m-NHMe, where n + m = 14, to figure out the positional preference of proline in α-helices. The relative free energy of each peptide was calculated by subtracting the free energy of the extended conformation from that of the α-helical one, which is used here as a measure of preference. The highest propensity is found for the peptide with proline at the N-terminus (i.e., Ncap + 1 position), and the next propensities are found at Ncap, N′ (Ncap − 1), and C′ (Ccap + 1) positions. These computed results are reasonably consistent with the positional propensities estimated from X-ray structures of proteins. The breaking in hydrogen bonds around proline is found to play a role in destabilizing α-helical conformations, which, however, provides the favored hydration of the corresponding N–H and C=O groups. The highest preference of proline at the beginning of α-helix appears to be due to the favored electrostatic and nonbonded energies between two residues preceding proline and the intrinsic stability of α-helical conformation of the proline residue itself as well as no disturbance in hydrogen bonds of α-helix by proline. The average free energy change for the substitution of Ala by Pro in a α-helix is computed to be 4.6 kcal/mol, which is in good agreement with the experimental value of ∼4 kcal/mol estimated for an oligopeptide dimer and proteins of barnase and T4 lysozyme.

Left-handed polyproline II helices (PPII) are contiguous elements of protein secondary structure in which the φ and ψ angles of constituent residues are restricted to around −75° and 145°, respectively. They are important in structural proteins, in unfolded states and as ligands for signaling proteins. Here, we present a survey of 274 nonhomologous polypeptide chains from proteins of known structure for regions that form these structures. Such regions are rare, but the majority of proteins contain at least one PPII helix. Most PPII helices are shorter than five residues, although the longest found contained 12 amino acids. Proline predominates in PPII, but Gln and positively charged residues are also favored. The basis of Gln's prevalence is its ability to form an i, i + 1 side-chain to main-chain hydrogen bond with the backbone carbonyl oxygen of the proceeding residue; this helps to fix the ψ angle of the Gln and the φ and ψ of the proceeding residue in PPII conformations and explains why Gln is favored at the first position in a PPII helix. PPII helices are highly solvent exposed, which explains why apolar amino acids are disfavored despite preferring this region of φ/ψ space when in isolation. PPII helices have perfect threefold rotational symmetry and within these structures we find significant correlation between the hydrophobicity of residues at i and i + 3; thus, PPII helices in globular proteins can be considered to be amphipathic.

Saliva and faecal samples were collected from hill cattle (no. = 10) given tannin-rich oak (Quercus incana) leaves in the north-west Himalayan region of India. Amino acid composition of the saliva samples after thawing to remove precipitated proteins by centrifugation, and dialysis (molecular weight cut off: 3500) to remove small moieties revealed 6·4 (s.d. 0·6) % proline, 15·6 (s.d. 0·6) % glutamine plus glutamate and 9·2 (s.d. 1·0) % glycine on molar basis. For Holstein Friesian cattle (no. = 4) which had no history of consumption of tannin-containing foods, these values were 6·5 (s.d. 0·4) %, 15·2 (s.d. 0·5) % and 9·8 (s.d. 0·7) % respectively. Proline concentration in the proteins present either as free or as tannin-protein complexes in the lyophilized faecal samples from hill cattle was 4·7 (s.d. 0·2) % (on molar basis) of the total amino acids and 5·3 (s.d. 0·2) % in Holstein Friesian cattle. In the faeces of oak-fed cattle, the tannin and condensed tannin levels on dry-weight basis were 0·81 (s.d. 0·20) % as tannin acid equivalent and 0·06 (s.d. 0·04) % as leucocyanidin equivalent respectively. For tannic acid, the relative affinity of salivary proteins, using the competitive binding assay, was about six-times higher than that of bovine serum albumin (BSA) and was of the same order as that of gelatin. Turbidity of complexes formed between salivary proteins or BSA and tannic acid showed proportionately about 0·50 lower turbidity for salivary proteins in 0-2 mol/I acetate buffer (pH 4·9 containing 0·17 mol/l NaCl) and proportionately about 0·84 lower turbidity in distilled water. The results suggest that unlike rats or mice, the proline-rich proteins do not appear to be of any physiological significance in the adaptation of cattle to tannins. However, the salivary proteins of cattle though not rich in proline, have a high affinity for tannins and these proteins have a high tendency to form soluble tannin-protein complexes.