Inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase by xylulose 1,5-bisphosphate

Xylulose 1,5-bisphosphate is a potent inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase. The enzyme was inhibited 50% at a xylulose 1,5-bisphosphate concentration of 0.56 micrometer and an enzyme concentration of 0.14 micrometer. When both ribulose 1,5-bisphosphate and xylulose 1,5-bisphosphate were added simultaneously to the enzyme, this inhibition appeared to be competitive. A preincubation of 20 to 30 min was needed for maximum inhibition. The inhibitory effect of this compound is probably exerted through its binding at the ribulose 1,5-bisphosphate active site, since both the carboxylase and oxygenase activities were inhibited similarly.