Heme environment in aldoxime dehydratase involved in carbon-nitrogen triple bond synthesis.

Resonance Raman spectra have been measured to characterize the heme environment in aldoxime dehydratase (OxdA), a novel hemoprotein, which catalyzes the dehydration of aldoxime into nitrile. The spectra showed that the ferric heme in the enzyme is six-coordinate low spin, whereas the ferrous heme is five-coordinate high spin. We assign a prominent vibration that occurs at 226 cm(-1) in the ferrous enzyme to the Fe-proximal histidine stretching vibration. In the CO-bound form of OxdA, the correlation between the Fe-CO stretching (512 cm(-1)) and C-O stretching (1950 cm(-1)) frequencies also supports our assignment of proximal histidine coordination.