Oxidation of d -Malic and β-Alkylmalic Acids by Wild-Type and Mutant Strains of Salmonella typhimurium and by Aerobacter aerogenes

Abstract

A mutant strain of Salmonella typhimurium (SL 1634 dml-51 ) capable of growth on d -malate as sole carbon source was shown to produce d -malic enzyme. This enzyme was absent in the parent wild-type strain which was unable to grow on d -malate. Growth of the mutant on d -malate also resulted in a greatly increased level of β-isopropylmalic enzyme compared with its level in the wild-type strain grown on citrate or l -malate. The d -malic and β-isopropylmalic enzymes, both of which catalyze a nicotinamide adenine dinucleotide- and Mg ++ -dependent oxidative decarboxylation of their respective substrates, were shown to be distinct enzymes by selective inhibition with erythro - dl -β-hydroxyaspartate and by other methods. Cell extracts of the mutant strain also oxidized dl -β-methyl-, dl -β-ethyl-, dl -β-propyl- and dl -ββ-dimethylmalates, in order of decreasing activity. dl -β-Methyl-malate was shown to be oxidized by both the d -malic and the β-isopropylmalic enzymes, whereas the oxidation of the other β-alkylmalates appeared to be effected exclusively by the β-isopropylmalic enzyme. β-Isopropylmalic enzyme activity was induced by d -malate but not by l -malate, showing that it behaved as a d -malictype enzyme. Growth of Aerobacter aerogenes on d -malate, which caused induction of d malic enzyme, resulted in only a small increase in the activity of β-isopropylmalic enzyme.