Abstract

A novel approach based on dc and ac cyclic voltammetric techniques to evaluate interfacial enzymatic activity is presented. As an illustrative example, the hydrolytic effect of phospholipase A2 (PLA2) on an l-α-dioleoylphosphatidylcholine (DOPC) monolayer adsorbed onto a mercury electrode surface has been studied and kinetic parameters have been evaluated. The enzymatic activity obtained in this study is of the order of 10-1 min-1. A dramatic effect of [Ca2+] on the hydrolysis of DOPC monolayers by PLA2 has been observed where the hydrolytic rate constant exhibits a peak-shaped dependence on [Ca2+] with a maximum rate at a Ca2+ concentration of about 6 mM. Ca2+ concentrations above 6 mM appear to have an inhibitory effect on the hydrolysis. Control studies with the nonhydrolyzable substrate analog, N-oleoyl-d-sphingomyelin (SM), demonstrate that the PLA2 does not simply displace the intact phospholipid molecules from the electrode surface. Thus, the observed electrochemical response arising from PLA2 is d...

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