Inhibition of ribulose 1,5-bisphosphate carboxylase/oxygenase by 2-carboxyarabinitol-1-phosphate

Abstract

In some plants, 2-carboxy-D-arabinitol 1-phosphate (CA1P) is tightly bound to catalytic sites of ribulose, 1,5-bisphosphate carboxylase/oxygenase (rubisco). This inhibitor's tight binding property results from its close resemblance to the transition state intermediate of the carboxylase reaction. Amounts of CA1P present in leaves varies with light level, giving CA1P characteristics of a diurnal modulator of rubisco activity. Recently, a specific phosphatase was found that degrades CA1P, providing a mechanism to account for its disappearance in the light. The route of synthesis of CA1P is not known, but could involve the branched chain sugar, hamamelose. There appear to be two means for diurnal regulation of the number of catalytic sites on rubisco: carbamylation mediated by the enzyme, rubisco activase, and binding of CA1P. While strong evidence exists for the involvement of rubisco activase in rubisco regulation, the significance of CA1P in rubisco regulation is enigmatic, given the lack of general occurrence of CA1P in plant species. Alternatively, CA1P may have a role in preventing the binding of metabolites to rubisco during the night and the noncatalytic binding of ribulose bisphosphate in the light.