An electrochemical study of the interfacial and conformational behaviour of cytochrome c and other heme proteins

An electrochemical investigation of the interfacial and conformational behaviour of microperoxidase and the heme proteins, cytochrome c, myoglobin and hemoglobin, has been made at the platinum electrode using cyclic voltammetry over the temperature range 273 to 363 K. Plateau values of surface charge density were obtained for increasing concentrations of protein in the bulk solution. The values were shown to increase with temperature until 333 K for cytochrome c and myoglobin, and 323 K for hemoglobin. At higher temperatures, the adsorption diminished due to denaturation and agglomeration of the protein. The absorbence measurements of the Soret band at 410 nm showed the same trends as the electrochemical results for cytochrome c and myoglobin. The absorbence of hemoglobin, however, decreased with increasing temperature from 273 K until it disappeared at temperatures above denaturation. The surface charge density was attributed to a flattening or denaturing of the protein at the electrode surface to allow adsorption of carboxylate groups accompanied by electron transfer at these anodic potentials. The number of carboxylate groups for each protein determined from a kinetic analysis agreed with the actual values and indicated that hemoglobin had dissociated into four polypeptide chains.