Krebs´ citric acid cycle

The citric acid cycle (CAC) has several functions in aerobic bacteria. Together with the pyruvate dehydrogenase multienzyme complex (PDHC), it completely oxidizes pyruvate and provides membrane-bound respiratory systems with reducing equivalents. An overview of the biochemistry and genetics of CAC enzymes in B. subtilis is presented in this chapter. B. subtilis, being a strict aerobe, runs a complete CAC, as is demonstrated by enzyme activity measurements with cell extracts or purified enzymes and by the ability of this bacterium to grow on most of the intermediates of the CAC as sole carbon source. 2-oxoglutarate dehydrogenase multienzyme complex (ODHC) belongs to the same family of enzymes as PDHC. Present knowledge of this enzyme, has been acquired from studies involving various B. subtilis mutants. The prosthetic groups of B. subtilis SQR and some of their properties are presented in this chapter. The occurrence of larger and smaller types of malate dehydrogenase seems not to be correlated with gram-positive or gram-negative bacteria as citrate synthase and succinate thiokinase are. Little information on the genetics of malate dehydrogenase in gram-positive bacteria is available, but B. subtilis mutants defective in this CAC enzyme have been isolated.