Ferricyanide-mediated oxidation of ferrous oxygenated and carbonylated myoglobin (Mb(II)-O-2 and Mb(II)-CO, respectively) is limited by O-2 and CO dissociation, respectively, then the transient deoxygenated derivative (Mb(II)) is rapidly oxidized. Here, kinetics of ferricyanide-mediated oxidation of ferrous nitrosylated sperm whale myoblobin (Mb(II)-NO) is reported. Unlike for Mb(II)-O-2 and Mb(II)-CO, ferricyanide reacts with Mb(II)-NO forming first a transient ferric nitrosylated species (Mb(III)-NO), followed by the (NO)-N-center dot dissociation from Mb(III)-NO. Values of the second-order rate constant for ferricyanide-mediated oxidation of Mb(II)-NO (i.e., for the formation of the transient Mb(III)-NO species) and of the first-order rate constant for (NO)-N-center dot dissociation from Mb(III)-NO (i.e., for Mb(III) formation) are (1.3 +/- 0.2) x 10(6) M-1 s(-1) and 7.6 +/-1.3 s(-1), respectively, at pH 8.3 and 20.0 degrees C. Since (NO)-N-center dot dissociation from Mb(II)-NO is very slow, and (unlike O-2 and CO) (NO)-N-center dot is a ligand for both Mb(II) and Mb(III), Mb(II)-NO can be oxidized without requiring (NO)-N-center dot dissociation. (c) 2007 Elsevier Inc. All rights reserved.