Vitamin interaction with glycine

Requirements for essential amino acids in poultry and pigs have been devised, and some of these are presented in Appendix 2, Tables A2.9 and A2.10. However, there are considerable complications associated with defining amino add requirements because of interactions between the essential amino acids, between essential and non-essential amino acids, and between amino acids and other nutrients. In chicks, the requirement for glycine is increased by low concentrations of methionine, arginine or B vitamins. Similarly, one amino acid may be converted to another. For example, if cystine or its metabolically active form cysteine is deficient in the diet, it can be synthesised by the animal from methionine. The requirement for methionine is therefore partly dependent on the cystine (or cysteine) content of the diet, and the two amino acids are often considered together (i.e. the requirement is stated for cystine -I- methionine). It should be noted, however, that the two are not mutually interconvertible methionine is not synthesised from cystine and therefore part of the total requirement must always be met by methionine. Phenylalanine and tyrosine have a similar relationship, and in the chick glycine and serine are interconvertible. 

In animals and humans, at intracellular pH, nearly all natural boron exists as boric acid, which behaves as a Lewis acid, and forms molecular additive compounds with amino- and hydroxy acids, carbohydrates, nucleotides, and vitamins through electron donor-acceptor interactions. In most of the commercial dietary boron supplements now available, boron is chelated with amino acids or with hydroxy acids (i.e., glycine, aspartic acid, or citric acid) in combination with vitamins. However, little is known about the molecular structure of these boron chelates. ... 

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