D-alpha-Hydroxyglutarate dehydrogenase of Rhodospirillum rubrum

D-alpha-Hydroxyglutarate dehydrogenase of R. rubrum grown anaerobically in the light was partially purified and some properties were investigated. 1. The enzyme catalyze stoichiometrically the dehydrogenation reaction of D-alpha-hydroxyglutarate into alpha-oxoglutarate, coupled with the reduction of 2, 6-dichlorophenolindophenol. 2. Cytochrome c2, cytochrome c, and ferricyanide are effective as electron acceptors with the crude enzyme but not with the purified one, whereas NAD+ and NADP+ are completely ineffective. The enzyme is thought to play a role in the electron transport system of the organism. 3. D-alpha-Hydroxyglutarate is virtually the sole substrate for the enzyme. The apparent activity against L-alpha-hydroxyglutarate is presumed to be due to contamination of the L-isomer sample with the D-isomer. The enzyme shows barely detectable activity against both isomers of malate and virtually no activity against DL-lactate and glycolate. 4. Both isomers of malate and oxalate, which are presumably substrate analogues, inhibit the enzyme activity. 5. The enzyme is not an inducible enzyme but rather is a constitutive one for R. rubrum, unlike from the enzyme of Pseudomonas putida which is an inducible enzyme for the catabolism of lysine.