Differential interactions of nitric oxide donors with rat oxyhemoglobin

To estimate the reaction of two primary redox-related species of nitric oxide (i.e. NO+ vs NO*) from a variety of NO donors, we employed the differential interactions of these NO forms with oxyhemoglobin (oxyHb) as a chemical assay. NO+ formation was estimated by the S-nitrosation reaction with oxyHb, and NO* formation via its reaction with the oxygen-heme complex of oxyHb. Under the conditions employed, all NO donors caused concentration-dependent formation of methemoglobin, indicative of NO* liberation. However, the extent of S-nitrosation was substantially different among the NO donors studied. A representative S-nitrosothiol, S-nitroso-N-acetyl-penicillamine, caused significantly more S-nitrosation than nitroglycerin, isobutyl nitrite, sodium nitroprusside, and 3-morpholino-sydnonimine (ANOVA, P < 0.05). These results indicated that NO donors can differ in their interactions with oxyHb, and possibly with other target proteins, in part because they liberate or transfer different ratios of NO redox forms. This difference may contribute, in part, to the diversity of pharmacological effects elicited by NO donors.