NI (II) AND PB (II) INHIBIT THE ENZYMATIC ACTIVITY OF DNA IN AN ELECTRON TRANSFER REACTION

Abstract

Introduction. Ni and Pb are metals with several suggested mechanisms for their toxicity on the biological systems. We have recently investigated involvement of DNA in an electron transfer reaction as an enzyme. In this reaction non- fluorescent dichlorofluorescin (LDCF) is converted to the dichlorofluorescein (DCF) in the presence of peroxides and hematin.
Methods. The fluorometric technique was used in this study. The pH effect on the reaction rate was investigated. The results showed that DCF has the maximum emission on tris buffer 0.05 Mat pH 8.4.
Results. DNA and carnosine catalyze the reaction, which proceeds by the electron transfer mechanism. The presence of carnosine is necessary for the catalytic action of DNA as a cofactor. Ni (II) and Pb (11) are the potent inhibitors of the reaction. The kinetic parameters and determined in the presence and absence of the above ligands.
Discussion. DNA, which has the electrical properties only in the double helical forms, acts as a catalyst in the conversion of LDCF to DCF. The existence of the carnosine, an endogenous dipeptide with antioxidant and free radical scavenging roles, is an important factor for the progress of the reaction. Both Ni (11) and Pb (II) inhibit the reaction. These metals could act as the electron pool to cause inhibition in such electron transfer reaction. This phenomenon could be related to the carcinogenic effect of these metals.