R. S. Gordon

METABOLISM OF OTHER D- AND L-HYDROXY ACIDS

I would like to describe the metabolism of certain of the alpha hydroxy acids, keeping in mind that enzymes involved in these processes are relatively nonspecific (that is, they can utilize a number of alpha hydroxy acids a s substrates). In fact, Blanchard et a/ . ’ reported some years ago tha t a crystalline enzyme from rat kidney behaved as a n hydroxy acid oxidase, a s well a s an L-amino acid oxidase. Indeed, one could speculate that many enzymes reported as ‘‘lactic’’ enzymes may really have evolved in order t o metabolize other alpha hydroxy acids. What are some of these other hydroxy acids; what is their importance? I would like to discuss the role tha t some hydroxy acids have in amino acid metabolism. We will focus our attention on mammalian and avian systems in order to suggest a special role for certain hydroxy acids in conserving the carbon skeletons of a few essential amino acids. A number of alpha hydroxy analogs of amino acids have been reported to promote the growth of rats or chicks fed diets low in, or devoid of, concentrations of the corresponding amino Since alpha hydroxy analogs will have the same number and types of stereoisomers as the amino acids to which they correspond, previous work has not been completely clear as t o whether or not there is any correlation between the activity of the D-isomer of the analog and the ability of the animal or bird to use the D-isomer of the corresponding amino acid. Initially, it was of interest to try to reconcile the stereoconversion of D-methionine with the utilization of hydroxy analog of methionine, as we felt, most certainly, tha t common pathways were involved.