Some properties of ribulose bisphosphate carboxylase extracted from tomato leaves

Ribulose bisphosphate carboxylase (EC 4.1.1.39) activity was very low in tomato leaf extracts unless prepared in the presence of Mg2+, HCO3- and polyclar AT. With young leaves, but not with fully-expanded leaves, the RuBP carboxylase activity extracted was increased by prolonged illumination of the leaves (≧2 h). The main effect of the light treatment was to increase the specific activity of the enzyme but there was also a small increase in RuBP carboxylase protein. Tomato leaf RuBP carboxylase in extracts had specific activities in the range 0.2–0–6 μmol CO2 min−1 mg−-1 total protein extracted, or 0.5–1.2 μmol CO2 min−1 mg−1 RuBP carboxylase, and an apparent Km (CO2) at 20 °C of 9.3 ± 1.2 μM (using a pK1∞' of 6.407).