Effects of salts of alkali earth metals and calcium chloride on the stability of cytochrome c and myoglobin

Abstract

This study suggests a procedure by which binding of denaturants could be detected without any additional information other than that provided in the denaturation profiles of proteins. Two predominantly α-proteins, namely ferricytochrome c and metmyoglobin were denatured by guanidine hydrochloride (GdnHCl) in the presence of low fixed concentrations of salts at 25°C and transition between native and denatured states was followed by absorbance measurements in the visible region (500-350 nm). The raw data were converted into transition curves from which C m the midpoint of GdnHCl-induced transition, and ΔG app, the free energy changes on denaturation were calculated assuming a two-state mechanism, and values of ΔG app at zero concentration of the denaturant were estimated. It has been observed (1) that chlorides of Na, K, Cs, and Rb do not affect the native conformation of proteins, (2) that GdnHCl-induced denaturations of proteins in presence and absence of sodium bromide, sodium perchlorate and salts of lithium and calcium are reversible, (3) that optical properties of the GdnHCl-denatured state of proteins remain unchanged in presence of the second denaturant, (4) C m, decreases with an increase in the denaturant concentration, and (5) that except for GdnHCl there exist one or more binding sites on the native proteins for the denaturants.