The metabolism of C2 compounds in micro-organisms. 2. The effect of carbon dioxide on the incorporation of [14C]acetate by acetate-grown Pseudomonas KB1

Abstract

The effect of non-radioactive CO2 on the incorporation of C14 into protein synthesized from ammonium C14-acetate by Pseudomonas KB 1 was studied. The addition of unlabeled bicarbonate or pyruvate depressed the initial rate of incorporation of isotope into protein. Cells growing in a stream of unlabeled CO2 synthesized protein of specific radio-activity 15-17% lower than that synthesized in the absence of added unlabeled CO2. Alanine and aspartate synthesized from Cl4-acetate in the presence and absence of unlabeled CO2 were degraded. Unlabeled CO2 did not affect the distribution of isotope within the alanine molecule but caused a uniform reduction of radioactivity in the carboxyl carbons of aspartate. These findings show that C02-fixation reactions play no part in the synthesis of alanine from acetate but participate in the formation of aspartate. The observed labeling patterns provide evidence for the operation of the glyoxylate cycle in these organisms.