NUTRITION AND METABOLISM OF MARINE BACTERIA VIII

Abstract

An acetate-activating system, condensing enzyme, aconitase, isocitric dehydrogenase, and a-ketoglutaric dehydrogenase have been shown to be present in cell-free extracts of a marine bacterium. Except for the acetate-activating system, which required K+, none of the enzymes could be shown to be specifically activated by Na+ or K+ salts. Aconitase and isocitric dehydrogenase required media of appropriate ionic strength (0.3 to 0.4) for optimal activity. The enzymes were rapidly inactivated during dialysis and the activity could not be restored by adding back to the system either Na+ or K+ salts or the ash of the bacterial extract. Cofactor requirements and other properties of the enzymes indicated their similarity to the corresponding enzymes in bacterial and other cells from non-marine sources. It was evident from these and other results that the specific requirement for Na+ for the oxidation of tricarboxylic acid cycle intermediates by whole cells could not be accounted for by a requirement of one or more enzymes of the cycle for this ion.