[Multiple molecular forms of ribulose diphosphate carboxylase from mung bean leaves].

Ribulose diphosphate carboxylase from Phaseolus aureus leaves is represented by four molecular forms differing in their carboxylase and oxygenase activities, molecular weights, sedimentation coefficients, electrophoretic mobilities in polyacrylamide gel, chromatographic behaviour upon elution on Sephadex G-200 and DEAE-cellulose, pH optima of carboxylase activity and pI values. In some parameters, e. g. molecular weight of the whole molecule (530 000), molecular weights of the large and the pH optima of the carboxylase and oxygenase activities (8.5 and oxygenase activities (2.4 and 0.09 units per mg of protein, respectively) and the pH optima of the carboxylase and oxygenase activities (8.5 and 9.3, respectively) form II differs from form I, which has a lower molecular weight (480 000), a higher oxygenase and a lower carboxylase activities (0.2 and 1.5 units per mg of protein, respectively) and a higher pH optimum of the carboxylase activity (9.0). Both forms I and II are composed of eight large and eight small subunits. The molecular weight of the large subunits of form I is lower than that of form II and is equal to 48 000. The respective pI values for forms I and II are 6.8 and 6.4. Forms III and IV as well as forms I and II produce distinct bands under ion-exchange chromatography on DEAE-cellulose. The carboxylase and oxygenase activities of form III are 0.7 and 0.04 units per mg of protein, respectively. Form IV has a higher oxygenase and a lower carboxylase activity (0.09 and 0.25 units per mg of protein, respectively). The corresponding molecular weights of forms III and IV are 530 000 and 480 000. The molecular weights of the large and small subunits of form II are 53 000 and 12 000, respectively; those of form IV -- 48 000 and 12 000, respectively.