Dual inhibitory effects of dimethyl sulfoxide on poly(ADP-ribose) synthetase

Dimethyl sulfoxide (DMSO), a solvent popularly used for dissolving water-insoluble compounds, is a weak inhibitor of poly(ADP-ribose) synthetase, that is a nuclear enzyme producing (ADP-ribose)(n) from NAD(+). The inhibitory mode and potency depend on the concentration of substrate, NAD(+), as well as the temperature of the reaction; at micromolar concentrations of NAD(+), the inhibition by DMSO is biphasic at 37 degrees C, but is monophasic and apparently competitive with NAD(+) at 25 degrees C. DMSO, on the other hand, diminishes dose-dependently and markedly the inhibitory potency of benzamide and other inhibitors. Other organic solvents, ethanol and methanol, also show a biphasic effect on the synthetase activity at different concentrations.