Influence of nucleoside triphosphates, inorganic salts, NADH, catecholamines, and oxygen saturation on nitrite-induced oxidation of rainbow trout haemoglobin.

Oxidation of rainbow trout haemoglobin (Hb) by nitrite proceeded via an initial lag phase followed by autocatalysis when the O2 saturation of the Hb was high. At low O2 saturations, the rate of methaemoglobin (metHb) formation was strongly reduced and autocatalysis was absent. Addition of adenosine triphosphate and guanosine triphosphate to oxyHb lowered the haemoglobin O2 affinity and O2 saturation and slowed down nitrite-induced metHb formation in a dose-dependent manner, the effect of GTP being larger than that of ATP. Reduced nicotinamide adenine dinucleotide (NADH) and the catecholamines adrenaline and noradrenaline did not affect O2 saturation in oxyHb solutions but significantly slowed down nitrite-induced metHb formation. Inorganic salts (NaCl, KCl, NaNO3) impeded the oxidation of oxyHb by nitrite in a manner that was dependent on salt concentration but independent of the type of salt. The mechanisms and physiological implication of the effects are discussed.