Isocitrate lyase and malate synthase in Pseudomonas indigofera. I. Suppression and stimulation during growth.

Howes, William V. (Washington State University, Pullman) and Bruce A. McFadden. Isocitrate lyase and malate synthase in Pseudomonas indigofera. I. Suppression and stimulation during growth. J. Bacteriol. 84:1216-1221. 1962.-Specific activities of isocitrate lyase and malate synthase from Pseudomonas indigofera were studied as a function of growth. Each activity maximized in the mid to late exponential phase. Effects upon levels of isocitrate lyase and malate synthase of each of several compounds supplied with ethanol to P. indigofera were next investigated. Compounds tested were glucose, glyoxylate, malate, and yeast extract. Each was added at various concentrations to ethanol. At higher concentrations, glucose, malate, and yeast extract suppressed both enzymatic activities. Malate synthase was more sensitive to suppression. Glyoxylate, at higher concentrations, suppressed isocitrate lyase but substantially stimulated malate synthase. There was no evidence for diauxic growth. Each substrate furnished with ethanol stimulated growth. The possibility that in vivo control of isocitrate lyase activity was partially exerted through feedback inhibition by succinate was examined. Succinate at 5.2 x 10(-3)m inhibited the enzyme in "soluble" preparations. Intracellular succinate concentrations did not vary significantly at each of three growth phases when exogenous succinate was supplied. Thus, regulation of isocitrate lyase activity through feedback inhibition by succinate seems unlikely.