Rat Liver Aminomalonate Decarboxylase

Abstract

Abstract Studies on the aminomalonate decarboxylase of rat liver indicate that this activity is a property of cytoplasmic serine hydroxymethylase. Thus, throughout purification of the enzyme, aminomalonate decarboxylase, serine hydroxymethylase and allothreonine aldolase exhibited the same relative activities. Competition between the several substrates was observed and resolution of the enzyme by treatment with d-alanine led to loss of all three activities. Cleavage of allothreonine by the enzyme in tritiated water gave S-glycine-2-t (in accord with earlier data which indicate retention of configuration during conversion of l-serine to glycine), but decarboxylation of aminomalonate by the enzyme in tritiated water gave both S- and R-glycine-2-t. Studies with specifically carboxyl-labeled [14C]aminomalonate confirmed the conclusion that the enzyme decarboxylates this amino acid in a nonspecific manner; this result is in contrast to that previously observed with aspartate β-decarboxylase which acts on a specific carboxyl group of aminomalonate. In contrast to cytoplasmic serine hydroxymethylase, mitochondrial serine hydroxymethylase does not catalyze the aldol cleavage of allothreonine or the decarboxylation of aminomalonate; this indicates that there is a significant difference between the active sites of these enzymes.