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Metabolism of [U-14C]-l-threonine and [U-14C]-l-phenylalanine by the isolated perfused udder

Published online by Cambridge University Press:  01 June 2009

R. Verbeke ,
E. Roets ,
Anne-Marie Massart-Leën  and
G. Peeters
R. Verbeke
Affiliation:
Physiological Department of the Veterinary Faculty, University of Ghent, Belgium
E. Roets
Affiliation:
Physiological Department of the Veterinary Faculty, University of Ghent, Belgium
Anne-Marie Massart-Leën
Affiliation:
Physiological Department of the Veterinary Faculty, University of Ghent, Belgium
G. Peeters
Affiliation:
Physiological Department of the Veterinary Faculty, University of Ghent, Belgium
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Summary

A lactating mammary gland of a goat was perfused for 9 h in the presence of [U-14C]-l-threonine and received adequate quantities of glucose, acetate and amino acids. Two lactating sheep udders were likewise perfused in the presence of [U-14C]-l-phenylalanine: the plasma levels of phenylalanine in the first of these experiments were 4 times higher than in the second.

In the [14C]threonine experiment, 4 % of the casein and 0·4 % of the expired CO2 were derived from threonine; 85 % of the threonine and 1·6 % of the glycine residues in casein originated from plasma threonine. Small 14C levels were found in glutamic acid, aspartic acid and serine of casein. The relative specific activities amongst the casein amino acids and the appearance of appreciable labelling in plasma glycine are consistent with the view that threonine is split by threonine aldolase.

In the [14C]phenylalanine experiments virtually no radioactivity was detected in CO2, lactose or citric acid, indicating that this substrate is not broken down by mammary tissue. In the second experiment, 96 % of the phenylalanine and 0·3 % of the tyrosine of casein originated from plasma phenylalanine. In the first experiment, a 30-fold higher 14C incorporation into casein tyrosine relative to phenylalanine was observed. The possible significance of the phenylalanine concentration in the plasma on the degree of conversion of phenylalanine into tyrosine within the mammary gland is discussed.

Type
Research Article
Information
Journal of Dairy Research , Volume 39 , Issue 2 , June 1972 , pp. 239 - 250
Copyright
Copyright © Proprietors of Journal of Dairy Research 1972

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