The photoactivation process of a photosensitive nitrilr hydratasc (NHase) from IUtorlococcus sp. N-771 has been invcstigatcd by "Fe M&.sbauer spectroscopy and magnetic susceptibility measurements in order toclarify the behavior of iron atoms in theennyme. MBssbauer spectn of inactive NHase gave two symmetric-doublet components indicating the presence of two iron species, while that of the active NHase gave a single symmetric doublet indicating the presence of a single iron species. Magnetic susceptibility measurcmcnts of the inactive and active HNase both showed small effective magnetic moments. These results led us to conclude that one of the two iron atoms incorporated in the NHase is oxidized during photoactivation, namely from a low spin ferrous 10 a low spin ferric stale. This is the first observation of an intramolecular photooxidation phenomena involving iron in a single protein molecule.

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