THE INTERCONVERSION OF α-AMINO-ACIDS, α-HYDROXY-ACIDS AND α-KETONIC ALDEHYDES. PART II

COKTENTS.2. The formation of methyl glyoxal from lactic acid.3. The formation of methyl glyoxal and ammonia from alanine. 4. The formation of methyl glyoxal from glucose. 5.The formation of other a-ketonic aldehydes from a-hydroxy acids and a-amino-acids.6.The fate of methyl glyoxal and phenyl glyoxal on perfusion through the liver.Formation of phenyl glyoxylic acid.i.The fate of methyl glyoxal and of Z-lactic acid in the glycosuric organism. Metabolism of Carbohydrates and ProteinsAmino-acids have been commonly regarded as extremely stable substances, at least in vitro, but' our observations tend to show that under suitable conditions, in aqueous solution, when due provision is made for the prompt removal of the products of their decomposition, both the a-amino-acids and oc-hydroxy-acids are in a state of unstable equilibriume2 Furthermore, we have been able to show that the decomposition of amino-acids with formation of ketonic aldehydes is not due to a complicated reaction dependent upon the presence of the nitrophenylhydrazine, for it has been possible to demonstrate ammonia formation from amino-acids under similar conditions, but in the absence of the hydrazine.tThe production of oc-ketonic aldehydes from or-amino-and cu-hydroxy-acids is of biochemical significance, partly on account of the existence of enzymes which we have named "glyoxalases" capable of converting the former substances into hydroxy-acids3 R.CO.CHO + H,O = R.CHOH.COOHMoreover, we have been able to gather a considerable amount of indirect, evidence indicating that a!-ketonic aldehydes may play a part in ihtermediary metabolism.Thus we 'find that methyl glyoxal yields glucose in the glycosuric organism just as do alanine and lactic acid, from which methyl glyoxal may be derived in vitro (section 7).In addition, it is possible to demonstrate, in vitro, the reverse change, 'namely, the conversion of glucose into methyl glyoxal under conditions which, apart from temperature, are comparable with those existing in the animal body (section 4).From the foregoing evidence and other that has been referred to in our previous paper, it appeared justifiable to construct a scheme which may crudely represent the interconversion of alanine, lactic acid, methyl glyoxal and glucose by a series of reversible reactions involving the addition or subtraction of water or ammonia.Of the various reactions indicated, the direct formation of alanine from methyl glyoxal is the only one that thus far has