Ribulose 1,5-bisphosphate carboxylase and oxygenase from Thiocapsa roseopersicina: activation and catalysis.

Ribulose 1,5-bisphosphate carboxylase/oxygenase purified from malate-grown Thiocapsa roseopersicina required Mg²⁺ for the activation of both carboxylase and oxygenase activities. Mg²⁺ was either not required or required at very low concentrations for catalysis by both enzyme activities. EDTA and dithiothreitol had no effect on ribulose 1,5-biphosphate oxygenase. The K_0.5 values with respect to Mg²⁺ for activation of the carboxylase and oxygenase activities were 8.4 and 2 mm, respectively. Ribulose 1,5-biphosphate carboxylase and oxygenase activities revealed differential sensitivities to 6-phosphogluconate. This ligand at 1 mm inhibited the carboxylase activity 30%, whereas the oxygenase activity was inhibited by 69%.