Araujo G M, Silva C B, Hasson-Voloch A
Laboratório de Físico-Química Biológica, Instituto de Biofísica Carlos Chagas Filho da Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Brasil.
Int J Biochem Cell Biol. 1996 Apr;28(4):491-7. doi: 10.1016/1357-2725(95)00146-8.
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.
我们已经确定了汞和镉对电鳗（Electrophorus electricus, L.）电器官中肌酸激酶活性的影响。该酶催化磷酸肌酸与镁腺苷 - 5'-二磷酸之间的转磷酸化反应，且含有必需的巯基。利用磷酸肌酸、腺苷 - 5'-二磷酸和镁这三种反应成分，分析了这些对巯基具有高亲和力的重金属对肌酸激酶活性的动力学影响。动力学数据采用非线性回归程序（适用于Windows的Sigmaplot）进行分析。两种金属在微摩尔范围内均抑制肌酸激酶活性，汞的抑制作用比镉更强。以磷酸肌酸为底物时，汞表现为混合部分双曲线型抑制剂，对腺苷 - 5'-二磷酸为非竞争性抑制剂，对镁则表现为竞争性抑制剂。对于两种底物磷酸肌酸或腺苷 - 5'-二磷酸，镉的抑制作用表现为典型的竞争性，而当反应混合物中的变量为镁时，镉的抑制作用为非竞争性。结果表明，汞的结合位点在磷酸肌酸位点处或附近，但与腺苷 - 5'-二磷酸的结合位点不同，而镉与这些底物竞争结合相同的巯基位点。
