Anabolic Ornithine Carbamoyltransferase of Pseudomonas

Abstract

The anabolic ornithine carbamoyltransferase [EC 2.1.3.3] of Pseudomonas appears to be extremely specialized. Unlike the other carbamoyltransferases studied, this enzyme catalyzes the phosphorolytic cleavage of citrulline with a very poor efficiency. The causes of this directed functional specialization are studied. Kinetic data and thermodynamic properties of the reaction showed that the reaction mechanism is the same as for ornithine carbamoyltransferases from other sources, i.e., of the sequential ordered type, where carbamoylphosphate is the 1st substrate to be bound and phosphate the last product to be released. The anabolic transferase of Pseudomonas is different from other ornithine carbamoyltransferases, for it forms a binary dead-end complex with citrulline, leading to inefficient binding of phosphate and citrulline to the enzyme. Therefore the phosphorolytic cleavage of citrulline is equally inefficient. The affinity of the enzyme for citrulline at its catalytic site is low as compared to other transferases.