l-Malic dehydrogenase and codehydrogenase of Bacterium coli

Abstract

Washed suspensions of Bad. coli contain malic de-hydrogenase. When suspensions of the organism are crushed in the Booth-Green mill (Biochem. Jour. 32, 855. 1938), the malic dehydrogenase is extracted from the cell and resides mainly in the liquid fraction of the crushed1 material. The malic dehydrogenase of the cdK-juiee requires the addition of coenzyme I and coenzyme. factor (diaphorase) for its action with methylehe blue. When suspensions of Bact. coli are boiled, coenzyme I is liberated from the cell and passes into the supernatant fluid obtained by centri-fuging. Bact. coli does hot inactivate cozyifiase at a significant rate when incubated with it. Organisms grown on agar or in tryptic broth do not contain the optimum amount of coenzyme to saturate their malic dehydrogenase; the "index of coenzyme saturation" varying greatly with the age of the culture. Bact. coli oxidises[long dash]malate aerobically, taking up 4 atoms of 0 per mol. malate oxidized. The oxidation is inhibited by 104 [image] cyanide. The extracted dehydrogenase will oxidize Z-malate aerobically in the presence of the following system: malate[long dash]dehydrogenase[long dash]coenzyme I[long dash]coenzyme factor[long dash]cyanide[long dash]methylene blue[long dash]O2. The variation of the conc. of various components was studied. Under these conditions the malate is oxidised to oxaloacetate which has been isolated as the 2,4-dinitro-phenyl-hydrazone. The dehydrogenase is reversible.