Resonance Raman Detection of the Fe2+−C−N Modes in Heme−Copper Oxidases:  A Probe of the Active Site

Resonance Raman spectroscopy has been employed to investigate the reduced cyano complexes of cytochrome aa(3) from bovine heart and Rhodobacter sphaeroides and of cytochrome bo(3) from E. coli. In the aa(3)-type oxidases, the frequency of the Fe-CN stretching mode is located at 468 cm(-1), and the bending Fe-C-N vibration, at 500 cm(-1). The fully reduced cytochrome bo(3)-CN complex gives rise to a stretching vibration at 468 cm(-1), a bending vibration at 491 cm(-1), and a stretching C-N vibration at 2037 cm(-1). The observed differences between aa(3) and bo(3) oxidases in the frequencies of the Fe-C-N group suggest a quantitative difference in the structure of the His-heme a(3)(2+)/Cu(B)(1+) and His-heme o(3)(2+)/Cu(B)(1+) binuclear pockets upon CN- binding.