Location of the non-heme iron center on the alpha subunit of photoreactive nitrile hydratase from Rhodococcus sp. N-771.

Nitrile hydratase (NHase) from Rhodococcus sp. N-771, which possesses a non-heme iron center binding nitric oxide (NO), is activated by light irradiation. To localize the iron center in the protein, we quantified Fe atoms and performed FTIR measurements of the isolated alpha and beta subunits. The native NHase and the isolated alpha subunit contained about 1.0 and 0.8 mol Fe per mol protein, respectively, whereas the beta subunit contained only a trace of Fe. An NO stretching band was observed at 1852 cm-1 in the FTIR spectrum of the alpha subunit, but not in that of the beta subunit. Upon light irradiation of the alpha subunit, the affinity of the Fe atom decreased and the NO band disappeared from the FTIR spectrum. These observations indicate that the non-heme iron center, which is responsible for the photoreaction, is present in the alpha subunit.