New function of enzyme involved in the formation of a carbon‐nitrogen triple bond

Abstract

We have studied microbial metabolism of nitrile at the protein and gene levels. We discovered a nitrile‐synthesizing enzyme linked with nitrile hydratase (which is an industrial enzyme used for the production of amide from nitrile) in the nitrile metabolism. The nitrile‐synthesizing enzyme, which is involved in the synthesis of a carbon‐nitrogen triple bond, is a unique enzyme, which catalyzes the dehydration of aldoxime [R‐CH=N‐OH] into nitrile [R‐CN] even in an aqueous solution. This enzyme contains a heme as the prosthetic group. Unlike the utilization of H2O2 or O2 as a mediator of the catalysis by other heme‐containing enzymes, this enzyme is notable for the direct binding of a substrate to the heme ion. We previously reported that ferrous enzyme, containing a five‐coordinated high‐spin heme and a histidine residue as its proximal ligand, is the reactive form of the enzyme, and that another histidine in the distal heme pocket plays a crucial role in the catalysis. We determined the crystal structure of the enzyme and clarified the detailed reaction mechanism. Here, we for the first time found catalase activity of the enzyme, when 10 mM H2O2 was used as a substrate. We also determined kinetic parameters of this reaction. Based upon the three‐dimensional structure of this enzyme, we have tried to construct a mutated enzyme, which shows higher activity than the wild type enzyme.