INFLUENCE OF ORGANIC AQUEOUS-MEDIA IN THE RNASE ACTIVITY OF SPLEEN PHOSPHODIESTERASE

The hydrolysis of yeast RNA by spleen phosphodiesterase has been carried out at different temperatures, in the presence of water-miscible organic solvents. Dimethyl sulfoxide, tetrahydrofuran, acetonitrile, N,N-dimethylformamide and 1,4-dioxane were used at 2 and 5% to analyse the influence of these organic sovents in the RNase activity of the enzyme at different Mg(II) concentrations. UV difference spectra of RNA have been carried out in these media. Hyperchromic and hypochromic effects were observed, depending on the experimental conditions. These effects are related to changes in the α-helical-random coil equilibrium of RNA. The RNase activity is maximal at pH = 5.2 and [Mg(II)] = 20mM in the absence of organic media. The orgainc solvents at 2 and 5% diminish the RNase activity. This finding is apparently related to the decrease in the dielectric constant of the medium, but not with the variation of pH produced by the presence of organic media, which favours the alteration of the RNA structure, making it less susceptible to hydrolysis by the enzyme. The apparent activation energy of the hydrolysis of RNA by spleen phosphodiesterase is near 4 kcal mol-1 in the presence and in the absence of very different solvents 2% THF and 2% DMSO. © 1990.