O2-mediated oxidation of ferrous nitrosylated human serum heme-albumin is limited by nitrogen monoxide dissociation

Human serum heme-albumin (HSA-heme-Fe) displays globin-like properties. Here, kinetics of O-2-mediated oxidation of ferrous nitrosylated HSA-heme-Fe (HSA-heme-Fe(II)-NO) is reported. Values of the first-order rate constants for O-2-mediated oxidation of HSA-heme-Fe(II)-NO (i.e., for ferric HSA-heme-Fe formation) and for NO dissociation from HSA-heme-Fe(II)-NO (i.e., for NO replacement by CO) are k = 9.8 x 10(-5) and 8.3 x 10(-4) s(-1), and h = 1.3 x 10(-4) and 8.5 x 10-(4) s(-1), in the absence and presence of rifampicin, respectively, at pH = 7.0 and T = 20.0 degrees C. The coincidence of values of k and h indicates that NO dissociation represents the rate limiting step of O-2-mediated oxidation of HSA-heme-Fe(II)-NO. Mixing HSA-heme-Fe(II)-NO with O-2 does not lead to the formation of the transient adduct(s), but leads to the final ferric HSA-heme-Fe derivative. These results reflect the fast O-2-mediated oxidation of ferrous HSA-heme-Fe and highlight the role of drugs in modulating allosterically the heme-Fe-atom reactivity. (C) 2011 Elsevier Inc. All rights reserved.