Purification of an Endogenous Inhibitor of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase

Abstract

In the leaves of some species, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco, EC 4.1.1.39) activity is substantially lower when measured following a night period than when measured after the leaves have been subjected to high light conditions for a period of time (1,2,3,). This phenomenon of predawn or dark inhibition of rubisco has been attributed to the presence of a small mol wt phosphorylated molecule which binds tightly at the enzyme’s active site (2,4) and contains 1 mol of P/mol of inhibitor (4). Binding of the inhibitor is sufficiently tight such that following purification of the enzyme most of the inhibitor remains bound (4). This fact was exploited to afford purification of the endogenous inhibitor from tobacco. Using a similar procedure the inhibitor has been purified from predawn leaves of potato and identified using NMR spectroscopy (see Gutteridge et al., these proceedings).