An Immunological Investigation of the Structure and Function of Ribulose 1,5-Bisphosphate Carboxylase

Abstract

1 Ribulose bisphosphate carboxylase has been purified to homogeneity, as judged by poly-acrylamide-gel electrophoresis, isoelectric focusing and analytical ultracentrifugation, from the leaves of the French bean, Phaseolus vulgaris. The enzyme, of specific activity 1.52 units/mg protein, had a sedimentation coefficient of 17.9 S at 10 mg protein/ml. 2 The subunits of the enzyme were separated by gel filtration in the presence of sodium dodecylsulphate and the molecular weights of the isolated subunits were estimated to be 55000 and 15300 by sodium dodecylsulphate-polyacrylamide gel electrophoresis. 3 Antibodies to the enzyme and its subunits were raised in rabbits and the reactions of the antisera were examined by gel diffusion and by quantitative precipitin analysis. Ribulose bis-phosphate carboxylase activity was inhibited by the anti-enzyme serum and by the anti-large-subunit serum, but not by the anti-small-subunit serum or by a control serum, suggesting that the large subunit of the enzyme contains the catalytic site. 4 Gel diffusion of the antisera against preparations of the enzyme and small subunits from bean and spinach-beet, Beta vulgaris, revealed that the partial immunological identity of the bean and spinach-beet enzymes was located in the large subunits.