COMPARISON OF THE INHIBITORY EFFECTS OF MERCURY AND CADMIUM ON THE CREATINE-KINASE FROM ELECTROPHORUS-ELECTRICUS (L)

We have determined the effects of mercury and cadmium on the creatine kinase activity of the electric organ of Electrophorus electricus (L.) which catalyses the transphosphorylation reaction between phosphocrea tine and magnesium adenosine-5'-di-phosphate and has essential sulfhyd ryl groups. The kinetic effects of these heavy metals, which have high affinity for sulfhydryl groups, on the creatine kinase activity were analysed with the three reaction components: phosphocreatine, adenosin e-5/-di-phosphate and magnesium, The kinetic data were analysed;with a non-linear regression program (Sigmaplot for Windows), Both metals in hibit creatine kinase activity in the micromolar range, mercury being a more potent inhibitor than cadmium, With phosphocreatine as substrat e, mercury behaved as a mixed partial hyperbolic inhibitor, non-compet itive inhibitor with adenosine-5'-di-phosphate, and with magnesium mer cury behaved as a competitive inhibitor, Cadmium inhibition was shown to be of a classical competitive nature with respect to both substrate s, phosphocreatine or adenosine-5'-di-phosphate, and non-competitive w hen magnesium was the variable in the reaction mixture, The results su ggest that the binding site of mercury is at or near the phosphocreati ne site, but it is not the same as adenosine-5'-di-phosphate, whereas cadmium competes with these substrates to bind at the same sulphydryl site. Copyright (C) 1996 Elsevier Science Ltd.