Photosynthesis in Rhodospirillum rubrum. IV. Isolation and characterization of ribulose 1,5-diphosphate carboxylase.

Abstract Ribulose 1,5-diphosphate carboxylase has been isolated from autotrophically cultured Rhodospirillum rubrum. The molecular weight is 120,000. The Km for ribulose 1,5-diphosphate is 83 mm, and for CO2 is 59 mm. The enzyme is inhibited by three important metabolites: citrate, an intermediate of the tricarboxylic acid cycle; inorganic phosphate; and 3-phosphoglyceric acid, the product of the reaction catalyzed by the carboxylase. Both the levels and the activity of ribulose 1,5-diphosphate carboxylase are apparently subject to metabolic control in this facultative photoautotroph.