The effects of low temperature acclimation of winter rye on catalytic properties of its ribulose bisphosphate carboxylase–oxygenase

Abstract

A comparison was made of the kinetics of the carboxylation reaction of bicarbonate–magnesium-activated ribulose biphosphate carboxylase–oxygenase purified from cold-hardened and unhardened winter rye (Secale cereale L. cv. Puma). The activity of the (NH 4 ) 2 SO 4− precipitated enzyme from hardened plants was stable at −20 °C for a month, whereas the form from unhardened plants was reversibly cold inactivated. The [Formula: see text] of the unhardened form increased more rapidly with decreasing pH below 8.2, but the estimated pK a of chemical groups associated with the active site was not affected by the cold hardening. The temperature dependencies of the [Formula: see text] of the two forms of the enzyme crossed at 10 °C with the effect that the catalysis of carboxylation by ribulose biphosphate carboxylase–oxygenase from Puma rye was most efficient in the temperature range to which the plants had been adapted.