Resonance Raman characterization of soluble guanylate cyclase expressed from baculovirus

Resonance Raman spectra of the alpha(1) beta(1) isoform of bovine lung soluble guanylate cyclase expressed from baculovirus have been measured. The spectra show that the ferric heme is five-coordinate high spin whereas the ferrous heme in the absence of added exogenous ligands is a mixture of six-coordinate low spin and five-coordinate high spin. In the Fe-CO-derivative, the correlation between the Fe-CO frequency (497 cm(-1)) and the C-O frequency (1959 cm(-1)) demonstrates that the proximal ligand in our preparation is histidine. The Fe-NO stretching frequency (found at 520 cm(-1)) and other spectral features of the ferrous Fe-NO-bound sGC are similar to those reported by Deinum et al. (1) and Yu et al. (2). These data indicate that although large preparation-dependent differences in the occupancy of the distal pocket exist, all the preparations have the same proximal histidine ligation and share the same mechanism of activation by NO.