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

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Abstract
The malate synthase activity detectable in crude extracts of Pseudomonas AM1 was 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 showed that it is distinct from citrate synthase [EC 4.1.3.7] which also hydrolyzes malyl-CoA. The malyl-CoA hydrolase has a low Km for malyl-CoA (7.0 .mu.M). A mutant of Pseudomonas AM1, ICT51, which is unable to grow on ethanol, malonate or 3-hydroxybutyrate, had an altered malyl-CoA hydrolase with a Km for malyl-CoA 30 times than that of the enzyme present in the wild-type organism. Two classes of revertants to growth on these substrates were isolated; those with a malyl-CoA hydrolase of similar Km to the wild-type and 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.