DNA as an enzyme: The effect of imidazole derivatives as cofactors and metal ions as activators or inhibitors
Objective: a highly sensitive spectrofluorometric method using dichlorofluorescin (LDCF) was employed to study the rate of electron transfer reaction in presence of DNA and some imidazole derivatives. Results: in our experiments, DNA possessed a unique enzyme like catalytic function in oxidative conversion of nonfluorescent LDCF to fluorescent dichlorofluorescein (DCF). The rate enhancement was associated with the turn over constant: k(p) = 10 s(-1) for DNA and cinnamoyl imidazole as a cofactor. A biphasic saturation curve was observed when the reaction velocities were measured at fixed concentrations of DNA and variable amounts of carnosine. Each of the biphasic trends gave the Scatchard values of V(ml)/K(ml) = 3.1 X 10(-5) and V(m2)/K(m2) = 5.1 X 10(-6) with K(ml) = 2.7 X 10(-5) M and K(m2) = 4.2 X 10(-4) M for carnosine. Although Ni (11) and Pb (11) induced inhibition in the rate of electron transfer reaction in presence of DNA and cinnamoyl imidazole or carnosine, metal ions such as Mg (11), Cd (11), Zn (11) and Fe (11) caused activation of DNA. The rates of the reactions showed strong dependency on electronegativity and conductivity of metal ions, namely the increase in activity of DNA in presence of each metal ion correlated inversely with the electronegativities of the metal and was also related directly to the conductivities of individual metal. These effects were observed both in activation and also inhibition of DNA reaction. Imidazole compounds, e.g., Histidine, N-trans cinnamoyl imidazole and imidazole along with Cd (11) produced further rate enhancement. The increase was several times greater with N-trans cinnamoyl imidazole. Conclusions: this effect could provide additional evidence for the importance of an intermediary cofactor that could facilitate the transfer of the electron from the reaction site to the DNA conductive chord. This was most guaranteed by the conjugated system provided by a compound such as N-trans cinnamoyl imidazole. (C) 2003 The Canadian Society of Clinical Chemists. All rights reserved.