Optical and enzymatic characterization of amino acids.

The susceptibility of a wide variety of a-amino acids to the action of Land of n-amino acid oxidases from different biological sources has been studied by a number of investigators (l-7). These studies have in general revealed the considerable differences in the rates of oxidation by these enzymes of amino acids of different chemical structure. It would perhaps be superfluous to undertake even a partial reinvestigation and extension of these valuable studies, were it not for the following considerations: (a) most of the amino acids employed were racemic, and there is no assurance that in each case the resistant isomer did not affect the initial oxidative rate of the susceptible isomer (S-10);’ (b) no comparative data were presented on the individual diastereoisomers of threonine, hydroxyproline, and isoleucine, while data on uncharacterized, commercially available preparations of m-isoleucine, as our experience has shown (12), may be considered highly suspect; and (c) the resolution of forty-six racemic amino acids conducted in this Laboratory during the past few years and the demonstration of the extremely high optical purity of the isomers obtained (12-40) have provided the opportunity of performing a systematic survey of the relative susceptibility of these individual isomers to Land to Damino acid oxidase preparations, and of investigating the properties of amino acids not previously studied by other investigators. As a further characterization of these isomers, their optical rotations have been determined under nearly identical conditions, both in 5 N HCI and in glacial acetic acid. To our knowledge, optical rotation data in the latter solvent, with the exception of a few isolated cases, have not been generally reported. For many of the amino acids, the magnitude of the rotation values in glacial acetic acid was found to be considerably higher than in HCl solutions, a fact which may be of use in the optical characterization of amino acids available only in very small quantities.