Enzymic Properties of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase Purified from Rice Leaves

Abstract
The enzymic properties of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase purified from rice (Oryza sativa L.) leaves were studied. Rice RuBPcarboxylase, activated by preincubation with CO2 and Mg2+ like other higher plant carboxylases, had an activation equilibrium constant (KcKMg) of 1.90 × 105 to 2.41 × 105 micromolar2 (pH 8.2 and 25°C). Kinetic parameters of carboxylation and oxygenation catalyzed by the completely activated enzyme were examined at 25°C and the respective optimal pHs. The Km(CO2), Km(RuBP), and Vmax values for carboxylation were 8 micromolar, 31 micromolar, and 1.79 units milligram−1, respectively. The Km(O2), Km(RuBP), and Vmax values for oxygenation were 370 micromolar, 29 micromolar, and 0.60 units milligram−1, respectively.