The Detection and Characterization of Several Conformational States of Cytochrome b5 Aporeductase during Reversible Denaturation

The reversible denaturation of cytochrome b5 reductase at pH 2.0 has been described. During the relatively slow process of recombination, several protein species have been detected by spectral and fluorescence measurements of nucleotide binding, by protein fluorescence changes, and by alterations in the number of reactive sulfhydryl groups. Mercuribenzoate and mersalyl were used to prepare stable derivatives of several forms of the aporeductase that appear during recombination. This series of reactions, and in particular the stable mercurial derivatives, thus provide an ideal system for examining the dependence of the tertiary structure of a monomeric flavoprotein upon its primary structure and chemical environment.