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Abstract
The influence of Mg(II) and organic solvents on the structure-activity relationship of spleen phosphodiesterase II was analyzed using UV and fluorescence spectroscopies. An increase in the RNase activity found in the presence of Mg(II) was related to the enzyme-Mg(II) interaction detected by UV spectroscopy. In the fluorescence spectra of phosphodiesterase strong hypochromic and bathochromic effects were observed when RNA was present at a concentration (52 μg ml−1) of the same magnitude as the concentration that inhibits the activity (Ki = 40 μg ml−1). The strong quenching observed in the presence of RNA shows the importance of large dynamic and static quenching of the Trp residues of the enzyme. The denaturation temperature, approx. 60°C, was detected by the pattern observed in the intensity of fluorescence versus temperature curve. Organic solvents produced an alteration in the enzyme conformation, detected by fluorescence. This alteration was diminished in the presence of Mg(II), which stabilizes the conformation of the enzyme.