Resonance Raman detection of the heme Fe(II)-NO/2-nitrovinyl species in myoglobin

Abstract

The six-coordinate heme Fe(II)-NO/2-nitrovinyl species in myoglobin has been detected and characterized by resonance Raman spectroscopy. The Fe(II)-14NO and 15N-O stretching frequencies of the ferrous heme nitrosyl/2-nitrovinyl species are detected at 560 and 1587 cm−1, frequencies that are similar to those observed in the Mb heme Fe(II)-NO species. For the 2-nitrovinyl (Ca=CbNO2) moiety, which is formed upon H-abstraction from the -CbH2 group, the νs(NO2) is observed at 1322 cm−1, the νas(NO2) at 1516 cm−1 and the ν(Ca=Cb14NO2)/ ν(Ca=Cb15NO2) at 1623/1615 cm−1. The frequencies of the 2-nitrovinyl are largely unaffected by NO2−/NO binding to the heme Fe(II)/(III). The properties of the six-coordinate heme Fe(II)-NO/2-nitrovinyl species are compared to those of six-coordinate heme Fe(II)-NO and the five-coordinate heme Fe(II)-NO species isolated from meat products.