AN ELECTROCHEMICAL STUDY OF THE INTERFACIAL AND CONFORMATIONAL BEHAVIOR OF CYTOCHROME-C AND OTHER HEME-PROTEINS

An electrochemical investigation of the interfacial and conformational behaviour of microperoxidase and the heme proteins, cytochrome c, myo globin and hemoglobin, has been made at the platinum electrode using c yclic voltammetry over the temperature range 273 to 363 K. Plateau val ues of surface charge density were obtained for increasing concentrati ons 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 du e to denaturation and agglomeration of the protein. The absorbence mea surements of the Soret band at 410 nm showed the same trends as the el ectrochemical results for cytochrome c and myoglobin. The absorbence o f 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 pr otein at the electrode surface to allow adsorption of carboxylate grou ps accompanied by electron transfer at these anodic potentials. The nu mber of carboxylate groups for each protein determined from a kinetic analysis agreed with the actual values and indicated that hemoglobin h ad dissociated into four polypeptide chains.