Characterization of a malate dehydrogenase in the cyanobacteriumCoccochloris peniocystis

✍ Scribed by Eric G. Norman; Brian Colman

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 666 KB
• Volume: 156
• Category: Article
• ISSN: 0302-8933
• DOI: 10.1007/bf00418183

✦ Synopsis

A malate dehydrogenase (MDH) was characterized from the cyanobacterium Coccochloris penio-cyst&. The enzyme was purified approximately 180-fold and had a molecular weight of about 90 000. The enzyme had a pH optimum of pH 6.7 to 7.5; a Km (malate) of 5.6 mM and Kms for NAD and NADP of 24 gM and 178gM, respectively, although similar Vmax were obtained with either pyridine nucleotide. Enzyme activity was inhibited by ATP, citrate, oxalacetate, acetyl CoA and CoA. Enzyme assays with uniformly 14C-labelled malate caused no 14CO2 release, indicating this MDH is not a malic enzyme. Electrophoresis and S-200 gel filtration of the partially purified enzyme indicated a single MDH was present in this preparation. A second, less abundant, MDH was present in crude extracts. The presence of MDH in this organism is consistent with the operation of a glyoxylate cycle which, in the absence of a TCA cycle, would provide organic acids required in secondary carbon metabolism. ATP inhibition of MDH may allow for light regulation of MDH activity since, in the light, oxaloacetic acid is generated by phosphoenolpyruvate carboxylase activity.