ACTIVITY REGULATION OF PHOTOREACTIVE NITRILE HYDRATASE BY NITRIC OXIDE

Nitrile hydratase (NHase) from Rhodococcus sp. N-771 is a novel enzyme that possesses a non-heme iron(III) center binding endogenous nitric oxide (NO). It is inactivated by aerobic incubation of cells in the dark, whereas the inactive form is converted to the active one by light irradiation. To clarify the mechanism of activity regulation in the NHase, we investigated the role of NO. When the inactive NHase was irradiated in the presence of Fe(II) ions and a spin trap, N-methyl-d-glucamine dithiocarbamate (MGD), three hyperfine lines from the nitrogen atom of the [(MGD)2-FeII-NO] complex were resolved, indicating that NO was released from the enzyme upon photoactivation. The amount of NO release was obtained as 0.99 ± 0.12 per enzyme (n = 4) by using an NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide. The active NHase was completely inactivated by exogenous NO, and upon photoirradiation 86% of the original activity was restored. FTIR, ESR, and UV−VIS absorption measurements...