Synthesis and Hydrolysis of Malyl-Coenzyme A by Pseudomonas AM1: an Apparent Malate Synthase Activity

The malate synthase activity detectable in crude extracts of Pseudomonas AM1 has been shown to be due to a coupling of a malyl-CoA hydrolase with malyl-CoA lyase and not due to a discrete malate synthase enzyme. The partial purification of this malyl-CoA hydrolase from Pseudomonas AM1 has shown that it is distinct from citrate synthase which also hydrolyses malyl-CoA. The malyl-CoA hydrolase has a low Km for malyl-CoA (7-0 muM). A mutant of Pseudomonas AM1, ICT51 (Taylor & Anthony, 1975), which is unable to grow on ethanol, malonate or 3-hydroxybutyrate, has been shown to have an altered malyl-CoA hydrolase with a Km for malyl-CoA 30 times higher than that of the enzyme present in the wild-type organism. Two classes of revertants to growth on these substrates have been isolated: (i) those with a malyl-CoA hydrolase of similar Km to the wild-type and (ii) those in which the malyl-CoA hydrolase activity remains the same as in the mutant ICT51. The nature of the mutation leading to the latter class of revertants is unknown.