Mechanistic insights provided by deletion of a flexible loop at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase

A purified loop-deletion mutant of Rhodospirillum rubrum devoid of carboxylase activity but retaining catalytic ability in the enolization of ribulose biphosphate was achieved to show that the catalytic impairment mainly involves the stage of carboxylation of the initial enediol (ate). This result is consistent with the mechanistic deductions of the crystallographic studies. The behavior of the mutant also supports an essential role for flexible loop 6 in the carboxylation transition state.