Abstract
NO was reported to activate guanylate cyclase and, recently, prostaglandin H synthase. NO interaction with the heme component in different hemeproteins is determined by ligand property, electronic configuration of the heme iron and the specific effects contributed by the protein structure. It is found that although NO interaction with the free heme provides some common rules of interaction, the consequences of NO binding to different hemeproteins should be dealt with individually.