Reductive nitrosylation of ferric human serum heme-albumin

Abstract

Heme endows human serum albumin (HSA) with heme-protein-like reactivity and spectroscopic properties. Here, the kinetics and thermodynamics of reductive nitrosylation of ferric human serum heme-albumin [HSA-heme-Fe(III)] are reported. All data were obtained at 20 °C. At pH 5.5, HSA-heme-Fe(III) binds nitrogen monoxide (NO) reversibly, leading to the formation of nitrosylated HSA-heme-Fe(III) [HSA-heme-Fe(III)-NO]. By contrast, at pH ≥ 6.5, the addition of NO to HSA-heme-Fe(III) leads to the transient formation of HSA-heme-Fe(III)-NO in equilibrium with HSA-heme-Fe(II)-NO+. Then, HSA-heme-Fe(II)-NO+ undergoes nucleophilic attack by OH- to yield ferrous human serum heme-albumin [HSA-heme-Fe(II)]. HSA-heme-Fe(II) further reacts with NO to give nitrosylated HSA-heme-Fe(II) [HSA-heme-Fe(II)-NO] . The rate-limiting step for reductive nitrosylation of HSA-heme-Fe(III) is represented by the OH--mediated reduction of HSA-heme-Fe(II)-NO + to HSA-heme-Fe(II). The value of the second-order rate constant for OH--mediated reduction of HSA-heme-Fe(II)-NO+ to HSA-heme-Fe(II) is 4.4 × 103 m-1·s -1. The present results highlight the role of HSA-heme-Fe in scavenging reactive nitrogen species. © 2010 FEBS.