EFFECTS OF SALTS OF ALKALI-EARTH METALS AND CALCIUM-CHLORIDE ON THE STABILITY OF CYTOCHROME-C AND MYOGLOBIN

This study suggests a procedure by which binding of denaturants could be detected without any additional information other than that provide d in the denaturation profiles of proteins. Two predominantly alpha-pr oteins, namely ferricytochrome c and metmyoglobin were denatured by gu anidine hydrochloride (GdnHCl) in the presence of low fixed concentrat ions of salts at 25 degrees C and transition between native and denatu red states was followed by absorbance measurements in the visible regi on (500-350 nm). The raw data were converted into transition curves fr om which C-m, the midpoint of GdnHCl-induced transition, and Delta G(a pp), the free energy changes on denaturation, were calculated assuming a two-state mechanism, and values of Delta G(app) at zero concentrati on of the denaturant were estimated. It has been observed (1) that chl orides of Na, K, Cs, and Rb do not affect the native conformation of p roteins, (2) that GdnHCl-induced denaturations of proteins in presence and absence of sodium bromide, sodium perchlorate and salts of lithiu m and calcium are reversible, (3) that optical properties of the GdnHC l-denatured state of proteins remain unchanged in presence of the seco nd denaturant, (4) C-m decreases with an increase in the denaturant co ncentration, and (5) that except for GdnHCl there exist one or more bi nding sites on the native proteins for the denaturants.