Metabolism of Sarcina Lutea: II. Isotopic evaluation of the routes of glucose utilization

Abstract

Sets of curves have been constructed which relate the degree of labelling of pyruvate molecules derived from the metabolism of glucose-1,2 and 6- 14C to the percentage participation of the hexose-monophosphate oxidative cycle in systems where this and the Embden-Meyerhof glycolytic sequence are the only routes of glucose catabolism in operation. The curves used in the final interpretation of the data assume that hexosemonophosphate formed in the cyclic operation of the hexosemonophosphate oxidative pathway is degraded by the two routes in the same proportion as the original glucose. The existence of a pool of hexosemonophosphate common to both pathways, which is inherent in this assumption, receives support from the good agreement obtained with the three different position-labelled glucose substrates. The method has been applied to the pyruvic acid produced from position-labelled glucose in the presence of arsenite by suspensions of lyophilized Sarcina lutea. Metabolism of glucose-U- 14C confirmed that there was no formation of pyruvate from endogenous sources but revealed a significant fixation of CO 2 in the carboxyl group of pyruvate. After correction for this CO 2 fixation, the results obtained indicate that glucose is metabolized aerobically by both the Embden-Meyerhof and hexosemonophosphate oxidative pathways in the approximate ratio of 70 to 30. Data on the assimilation of glucose-U- 14C and 1- 14C suggest that this ratio does not vary appreciably during metabolism. Thus, although Sarcina lutea is unable to utilize glucose anaerobically, Embden-Meyerhof glycolysis constitutes the major aerobic pathway.