Vitamin B12, cobalamin, is indispensable for humans owing to its participation in two biochemical reactions: the conversion of l-methylmalonyl coenzyme A to succinyl coenzyme A, and the formation of methionine by methylation of homocysteine. Eukaryotes, encompassing plants, fungi, animals and humans, do not synthesise vitamin B12, in contrast to prokaryotes. Humans must consume it in their diet. The most important sources include meat, milk and dairy products, fish, shellfish and eggs. Due to this, vegetarians are at risk to develop a vitamin B12 deficiency and it is recommended that they consume fortified food. Vitamin B12 behaves differently to most vitamins of the B complex in several aspects, e.g. it is more stable, has a very specific mechanism of absorption and is stored in large amounts in the organism. This review summarises all its biological aspects (including its structure and natural sources as well as its stability in food, pharmacokinetics and physiological function) as well as causes, symptoms, diagnosis (with a summary of analytical methods for its measurement), prevention and treatment of its deficiency, and its pharmacological use and potential toxicity.

Chloroacetamide and thiocarbamate herbicides have many properties in common: both herbicide classes are effective only as preemergence herbicides; they inhibit early seedling growth and cause similar injury symptoms in susceptible species; they are detoxified in plants by glutathione conjugation; they have a similar spectrum of selectivity; they can be applied safely in certain susceptible grass crops when applied with antidotes; and they can inhibit the synthesis of lipids, isoprenoids, and other metabolic processes requiring coenzyme A. It can be hypothesized that these similarities are due to the ability of the chloroacetamides and the sulfoxide of thiocarbamates to bind covalently to enzymes, coenzymes, or metabolic intermediates containing sulfhydryl (-SH) groups.

Exchange of RNA structural domains through recombination can be used to engineer RNAs with novel functions and may have played an important role in the early evolution of life. The degree of function an RNA element retains upon recombination into a new sequence context is a measure of how deleterious or beneficial recombination will be. When we fused pairs of aptamers previously selected to bind coenzyme A, chloramphenicol, or adenosine, the chimerae retained some ability to bind both targets, but with reduced binding activity both in solution and on affinity resins, probably due to misfolding. Complex populations of recombined RNAs gave similar results. Applying dual selection pressure to recombined populations yielded the combinations that were best suited to binding both targets. Most reselected RNAs folded into the active conformation more readily than chimerae built from arbitrarily chosen aptamers, as indicated both by solution Kd measurements and affinity resin binding activity. Deletion/selection experiments confirmed that the sequences required for binding are fully contained within the respective domains and not derived from interaction between the domains, consistent with the modular architecture of their original design. The combinatorial nature of the recombination methods presented here takes advantage of the full sequence diversity of the starting populations and yields large numbers of bifunctional molecules (106 to more than 1012). The method can be easily generalized and should be applicable to engineering dual-function RNAs for a wide variety of applications, including catalysis, novel therapeutics, and studies of long-range RNA structure.