l-α-Glycerophosphate dehydrogenase, a component of an oxidase system in Trypanosoma rhodesiense

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Abstract
An enzyme has been found in particulate preparations of Trypanosoma rhodesiense which catalyses the oxidation of L-[alpha]-glycerophosphate to dihydroxyacetone phosphate in the presence of either phenazine methosulphate or 2:6-dichlorophenol-indophenol as electron acceptors. The enzyme has been termed an anaerobic L-[alpha]-glycerophosphate dehydrogenase. A partly purified particulate fraction under optimum conditions with phenazine methosulphate as electron acceptor catalyzed an O2 uptake which corresponded to a Q302 of about 1900. In the phenazine methosulphate assay procedure, the optimum enzyme activity in 2-amino-2-hydroxymethylpropane-l:3-diol (tris) buffer was about pH 8. The values of Km for substrate and electron acceptor were 9[center dot]0 and 0[center dot]34 m[image] respectively. L-[alpha]-Glycerophosphate-dehydrogenase activity was inhibited by certain thiol-group reagents. Inhibition by p-chloromercuribenzoate could be reversed by glutathione. The enzyme was insensitive to arsenite and Cd2+ ions. Prolonged incubation with either oxidized glutathione or cyanide had no significant effect on enzyme activity. Inhibition of enzyme activity by hydrogen peroxide was enhanced in a catalytic manner by either extracts of enzyme ash or Cu2+ ions. 8-Hydroxyquinoline almost completely protected the enzyme from these agents and this chelating agent was added as a routine in the assay procedure to protect the enzyme from hydrogen peroxide formed during the auto-oxidation of the reduced acceptor. A comparison of the activities of both L-[alpha]-glycerophosphate oxidase and the corresponding dehydrogenase was made on portions of the same preparation. The effects of p-chloromercuribenzoate were also studied. The results are consistent with the view that the dehydrogenase is a component of the oxidase system and that the former contains the thiol group that is essential for the activity of the oxidase.

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