Reactions of phospholipase A(2) at a mercury electrode surface

Cyclic voltammetric techniques (dc and ac) have been employed to probe the interfacial interaction of porcine pancreatic phospholipase A(2)(PLA(2)) with mercury. A reaction mechanism based on the interaction of cystine residues (disulfide) with mercury is presented. It appears that the interfacial electrical properties play an important role in determining the surface behavior of adsorbed PLA(2) molecules. For instance, the predominant step of the electron transfer process is dependent on the electrode surface properties, including the surface concentration of PLA(2) and the fraction of free surface mercury sites. In addition, the local pH at the interface and interfacial buffer capacity were also found to be important factors in the surface reaction mechanism. Studies of the electron transfer kinetics showed that the transfer coefficient (alpha) was somewhat less than 0.50, and the rate constant (k) was of the order of 10(3) s(-1). From ac cyclic voltammetric studies it was determined that the adsorbed PLA(2) layer corresponded to a capacitor of about 6 mu F/cm(2) and that the faradaic component of the interfacial capacitance was about 1 mu F/cm(2).