Microenvironmental manipulation of the observed michaelis constant of ribulose diphosphate carboxylase.

Urease and ribulose 1, 5-diphosphate carboxylase can be bound to Sepharose to give an immobilized two-enzyme system which catalyzes the reaction urea --> H(2)CO(3) --> phosphoglyceric acid. The observed Km of the system for urea approaches the lower value for urease when carboxylase levels on the gel exceed urease levels. If a similar system operates in the chloroplast, the high Km (H(2)CO(3)) of ribulose 1,5-diphosphate carboxylase may not be metabolically significant.