ADSORPTION DYNAMICS OF A PHOSPHOLIPASE A(2) ONTO A MERCURY-ELECTRODE SURFACE

Rapid cyclic voltammetry has been employed to investigate the electrochemical behavior of porcine pancreatic phospholipase A(2) (PLA(2)) adsorbed onto a hanging mercury drop electrode surface. The electrochemical response of PLA(2) exhibits a pair of voltammetric peaks which are ascribed to the reduction/oxidation of cystine/cysteine residues within the enzyme strongly adsorbed on mercury surfaces over the pH range of 0.77-8.50. Based on theoretical fits to the data, the adsorption process, under all experimental conditions, is found to be kinetically controlled. In addition, the adsorption appears to be consistent with a Frumkin adsorption isotherm with a small repulsive interaction. Both pH and temperature have a dramatic effect on the adsorption behavior in terms of the adsorption rate, equilibrium coverage, and molecular conformation.