Resonance Raman spectroscopic investigation of structural changes of CO‐heme in soluble guanylate cyclase generated by effectors and substrate

The influence of the effectors YC‐1 and BAY on the CO‐heme structure of bovine lung soluble guanylate cyclase (sGC) was investigated with resonance Raman spectroscopy. The effectors produced a five‐coordinate (5c) CO‐heme in addition to the His‐bound six‐coordinate (6c) CO‐heme, and both their Soret maxima were determined by simulation. On the basis of the absorption intensity, the amount of the 5c species was not dominant, in contrast to the high activity. The heme structural features common to the 5c and 6c CO‐hemes generated by effectors are that the vinyl and propionate side chains are more coplanar to the pyrrole rings. The out‐of‐plane Raman bands were observed only for the 5c species, for which the saddling and propeller distortions of heme were deduced to be large. The Fe CO stretching bands of the 5c species at 522 cm⁻¹ and of the 6c species at 488 cm⁻¹ were most enhanced upon excitation at 407 and 422 nm, respectively, which is consistent with the simulated spectra. Unexpectedly, the ¹³C¹⁸O isotope sensitivity appeared in low wavenumber porphyrin modes. From these observations, we propose that the high catalytic activity of sGC‐CO in the presence of effectors is a result of the concerted effects of protein conformational changes triggered by certain local interactions between the heme side chains and effectors/substrate in the heme pocket, which partly induce the cleavage of the Fe Hisβ 105 bond. Copyright © 2010 John Wiley & Sons, Ltd.