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J Bacteriol. 1972 October; 112(1): 427-433
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

CO₂-Fixing Enzymes in a Marine Psychrophile

Departamento de Bioquímica, Facultad de Ciencias Bioquímicas Universidad Nacional de Rosario, Suipacha 570, Rosario, República Argentina

ABSTRACT

A psychrophilic marine Pseudomonas was found to contain phosphoenolpyruvate (PEP) carboxylase and an adenosine triphosphate-linked PEP carboxykinase. Some properties of these CO₂-fixing enzymes were compared with those homologous enzymes from the terrestrial mesophile Enterobacter cloacae. The PEP carboxylases from both organisms were activated by acetyl-coenzyme A (CoA) and inhibited by L-aspartate. The enzyme from Pseudomonas was less dependent on the presence of the activator, but maximal activation was attained at acetyl-CoA concentrations much lower (50 µM) than those required to saturate the enzyme from E. cloacae. In both cases the main effect of acetyl-CoA was to decrease the K_m value for PEP. The activity of PEP carboxylase from Pseudomonas was only slightly inhibited by NaCl, KCl, or NH₄Cl up to 100 mM, whereas the enzyme from E. cloacae was inhibited by about 70% under similar experimental conditions. Both PEP carboxylase and PEP carboxykinase from Pseudomonas showed considerably lower thermal stability than their counterparts from E. cloacae. Our results suggest that the CO₂-fixing enzymes from a marine Pseudomonas and E. cloacae are similar in nature and regulation, but they differ in properties related to the peculiar conditions of the marine environment.