title: Comparison of the inhibitory effects of mercury and cadmium on the creatine kinase from Electrophorus electricus (L).
abstract: 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 phosphocreatine and magnesium adenosine-5'-di-phosphate and has essential sulfhydryl 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, adenosine-5'-di-phosphate and magnesium. The kinetic data were analysed with a non-linear regression program (Sigmaplot for Windows). Both metals inhibit creatine kinase activity in the micromolar range, mercury being a more potent inhibitor than cadmium. With phosphocreatine as substrate, mercury behaved as a mixed partial hyperbolic inhibitor, non-competitive inhibitor with adenosine-5'-di-phosphate, and with magnesium mercury behaved as a competitive inhibitor. Cadmium inhibition was shown to be of a classical competitive nature with respect to both substrates, phosphocreatine or adenosine-5'-di-phosphate, and non-competitive when magnesium was the variable in the reaction mixture. The results suggest that the binding site of mercury is at or near the phosphocreatine 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.
authors.affiliation: Laboratório de Físico-Química Biológica, Instituto de Biofísica Carlos Chagas Filho da Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Brasil.
authors.forename: G M
authors.initials: GM
authors.lastname: Araujo
authors.forename: C B
authors.initials: CB
authors.lastname: Silva
authors.forename: A
authors.initials: A
authors.lastname: Hasson-Voloch
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D019256:Cadmium Chloride / Q000494:pharmacology*; D003402:Creatine Kinase / Q000037:antagonists & inhibitors*; D004557:Electric Organ / Q000187:drug effects* / Q000201:enzymology; D004593:Electrophorus / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007700:Kinetics; D016014:Linear Models; D008274:Magnesium / Q000378:metabolism; D008627:Mercuric Chloride / Q000494:pharmacology*; D010725:Phosphocreatine / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D010725:Phosphocreatine; D008627:Mercuric Chloride; D000244:Adenosine Diphosphate; D003402:Creatine Kinase; D008274:Magnesium; D019256:Cadmium Chloride