S-nitrosohemoglobin: a biochemical perspective.

It has been suggested that S-nitrosohemoglobin (HbSNO) is an oxygen-dependent mediator of nitric oxide delivery to vascular smooth muscle cells, thus regulating vascular tone and blood flow. Central to this much-debated hypothesis is the concept that our previous understanding of the interaction between nitric oxide and ferrous hemoglobin was deficient. In this review we will examine the chemical and biochemical mechanisms for the formation of HbSNO, the properties of HbSNO, and the release of nitric oxide from HbSNO. This review concludes that although novel reactions of nitric oxide, nitrite, and S-nitrosothiols with hemoglobin have been uncovered, there is little evidence to support the notion that the interaction of nitric oxide with ferrous hemoglobin is more complex than had been previously established.