Purification and properties of ribulose 1,5-bisphosphate carboxylase from sunflower leaves.

Extracts from sunflower leaves possess a high ribulose-1,5-bisphosphate (RuBP) carboxylase capacity but this enzyme activity is not stable. A purification procedure, developed with preservation of carboxylase activity by MgSO4, yielded purified RuBP carboxylase with high specific activity (40 nkat mg(-1) protein). Measurement of kinetic parameters showed high Km values (RuBP, HCO 3 (-) ) and high Vmax of the reaction catalyzed by this sunflower enzyme; the results are compared with those obtained for soybean carboxylase. Enzyme characteristics are discussed in relation to stabilization and activation procedures and to the high photosynthesis rates of this C3 species.