Red Blood Cell Membrane-Facilitated Release of Nitrite-Derived Nitric Oxide Bioactivity

Abstract

The reduction of nitrite by deoxyhemoglobin to nitric oxide (NO) has been proposed as a mechanism for the transfer of NO bioactivity from the red blood cell (RBC) to the vasculature. This transfer can increase vascular dilatation. The major challenge to this hypothesis is the very efficient scavenging of NO by hemoglobin, which prevents the release of NO from RBCs. Previous studies indicate that the reaction of nitrite with deoxyhemoglobin produces two metastable intermediates involving nitrite bound to deoxyhemoglobin and a hybrid intermediate [Hb(II)NO(+) ↔ Hb(III)NO] where the nitrite is reduced, but unavailable to react with hemoglobin. We have now shown how unique properties of these intermediates provide a pathway for the release of NO bioactivity from RBCs. The high membrane affinity of these intermediates (>100-fold greater than that of deoxyhemoglobin) places these intermediates on the membrane. Furthermore, membrane-induced conformational changes of the nitrite-reacted intermediates facilitate the release of NO from the hybrid intermediate and nitrite from the nitrite-bound intermediate. Increased membrane affinity, coupled with facilitated dissociation of NO and nitrite from the membrane-bound intermediates, provides the first realistic mechanism for the potential release of NO and nitrite from the RBC and their potential transfer to the vasculature.

Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia

“…A recent study proposed that only 25% of nitrite is directly reduced into NO, while the rest of the nitrite forms two metastable intermediates of [Fe 2+ Hb···NO 2 − ] and [Fe 3+ Hb-NO ↔ Fe 2+ Hb-NO + ], which holds a >100-fold affinity for the membrane. The proximity of these species to the RBC membrane makes NO release and export possible, which should occur after conformational changes of Hb induced by the presence of the membrane (157). …”

HbE/β-Thalassemia and Oxidative Stress: The Key to Pathophysiological Mechanisms and Novel Therapeutics

“…This radical can either oxidize ferrous nitrosylheme to yield the ferric NO-heme derivative (Reaction 4a, Table 3) or react directly with the ferrous hemebound nitric oxide radical to produce N 2 O 3 ( Table 3, Reaction 4b) (78). Both ferric NOHb (via production of either NO + or N 2 O 3 ) (Table 3, Reactions 5b, 5c) (78,153,157) and N 2 O 3 generated from NOHb (Table 3, Reaction 4b) are potential Snitrosating agents that could generate SNOHb, GSNO, and CysSNO. These reactions, subsequent to the NR reaction, are still not fully tested and evaluated.…”

Modulation of Local and Systemic Heterocellular Communication by Mechanical Forces: A Role of Endothelial Nitric Oxide Synthase

“…It was proposed that compartmentalization of NO production in RBCs by formation of protein complexes on the RBC membrane ( e.g ., deoxyHb, AE1/band 3, and Rh-protein channels) facilitates NO production under hypoxic conditions and its export (60). Recently, it was shown that deoxyhemoglobin forms a complex with band 3 on the membrane of RBCs and that the stability of the complex depends on the oxygenation state of hemoglobin (124). Another possibility proposed by us is the presence of specific protein targets within the RBCs, leading to activation of downstream signaling and or protection of NO by local conversion of hemoglobin into methemoglobin (28).…”