ELECTRON-PARAMAGNETIC-RESONANCE SPECTRAL EVIDENCE FOR THE FORMATION OF A PENTACOORDINATE NITROSYL-HEME COMPLEX ON SOLUBLE GUANYLATE-CYCLASE

Nitric oxide (.NO) is an important intercellular signaling agent throu ghout the animal kingdom. The majority of the effects of .NO is due to the direct stimulation of soluble guanylate cyclase (sGC). It has bee n proposed that .NO activates sGC by interacting with a heme moiety on the enzyme. The electron paramagnetic resonance (EPR) spectra of the ferrous-[N-14/N-15] nitrosyl complexes of the purified enzyme have bee n obtained The spectrum of the [N-14]nitrosyl-sGC complex was almost i dentical to that of a 5-coordinate nitrosyl-heme model compound, indic ating that the nitrosyl complex formed on sGC is 5-coordinate. Hyperfi ne coupling constants and g-values were determined from computer simul ations of the EPR spectra. Electronic absorption spectroscopy was used to show that the 5-coordinate nitrosyl complex on sGC forms under con ditions that are typically used to assay activation of the enzyme. (C) 1995 Academic Press, Inc.