Metabolism of Sarcina lutea IV. Patterns of oxidative assimilation

Abstract

Freshly harvested or lyophilized cells of Sarcina lutea assimilate carbohydrate during the oxidation of glucose and a linear relationship exists between the glucose utilized and the carbohydrate deposited. The product appears to be a polymer composed of glucose units and it may be utilized in the absence of exogenous glucose. Experiments with [U- 14C] ★★ ★ [U- 14C] uniformly labelled with 14C. and [3,4- 14C 2]glucose show that 55% of the carbon atoms of glucose are assimilated without appreciable dilution, while the lower incorporation of radioactivity from [I- 14C]glucose reflects the formation of unlabelled hexose from this substrate via the pentosephosphate cycle. Assimilation of pyruvate or acetate does not yield polysacchride (or poly-β-hydroxybutyrate) and the assimilatory mechanism is shown by position-labelled substrates to depend on the tricarboxylic acid cycle. The carboxyl group of pyruvate is virtually eliminated while C-3 is incorporated to a greater extent than C-2; in the analogous case of acetate incorporation of C-2 exceeds that of C-I. The data indicate that glucose is not assimilated via pyruvate and support the previous observation that under the conditions employed glycolysis is not reversible from pyruvate to glucose. On the other hand, polysaccharide formation from glycerol shows reversibility from triose, or an alternative route from triose to glucose. Comparisons are made of the distribution in various fractions of the cell of the radioactivity assimilated from [U- 14C]glucose, [3- 14C]pyruvate and [2- 14C]acetate.