Assignment of Protoheme Resonance Raman Spectrum by Heme Labeling in Myoglobin

Resonance Raman (RR) spectra are reported for myoglobin reconstituted with seven heme isotopomers which are labeled with 15N and meso-D4 in the porphyrin skeleton or at the vinyl and propionate substituents. The RR bands are assigned to the porphyrin in-plane and out-of-plane modes as well as to the internal vibrations of substituents on the basis of the observed isotope shifts. The issue of vinyl substituent effects is revisited, and bands are assigned to the 2- or 4-vinyl group from selective deuteration shifts. Contributions of the aliphatic propionate groups are also revealed in the RR spectrum. The protein influence on the heme structure is reflected in the activation of several out-of-plane modes in the low-frequency region.