Mechanism of Ribulose-Diphosphate Carboxydismutase Reaction

Ribulose-1,5-P2 labelled with tritium in the C-3 position was converted to 2 moles of phospho-glyceric acid by the carboxydismutase. Over 98% of the radioactivity was found in the water, less than 0.1% being in phosphoglyceric acid, indicating that the proton lost from the 3 position of the substrate does not contribute to the formation of product. The tritiated substrate reacts at only 20% the rate of the normal carrier species. Neither substrate nor product show significant proton exchange with the medium due to the enzyme.