Catalysis of S-Nitrosothiols Formation by Serum Albumin: The Mechanism and Implication in Vascular Control

Nitric oxide (NO·) is a short-lived physiological messenger. Its various biological activities can be preserved in a more stable form of S-nitrosothiols (RS-NO). Here we demonstrate that at physiological NO· concentrations, plasma albumin becomes saturated with NO· and accelerates formation of low-molecular-weight (LMW) RS-NO in vitro and in vivo. The mechanism involves micellar catalysis of NO· oxidation in the albumin hydrophobic core and specific transfer of NO+ to LMW thiols. Albumin-mediated S-nitrosylation and its vasodilatory effect directly depend on the concentration of circulating LMW thiols. Results suggest that the hydrophobic phase formed by albumin serves as a major reservoir of NO· and its reactive oxides and controls the dynamics of NO·-dependant processes in the vasculature.