Conformational Changes in Deoxyribonuclease I in Anionic and Cationic Surfactant Solutions

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The effect of sodium dodecylsulfate (SDS) and deodecyltrimethylammonium chloride (DTAC) on the conformation of bovine pancreatic deoxyribonuclease I (DNase I, EC 3.1.21.1) has been studied by using fluorescence and circular dichroism methods as a function of surfactant concentration. About 60% of the fluorescence was quenched in the presence of 1 mM SDS, indicating the partial conformational transition of DNase I; the conformational susceptibility of DNase I to SDS was reduced by Ca²⁺ ions. The free energy changes were evaluated at 4.0±0.1 kcal·mol^-1 in the presence of 5 mM Ca²⁺ ions and 2.5±0.1 kcal·mol^-1 in the absence of Ca²⁺ ions. No fluorescence changes occurred in DTAC solution. The residue ellipticity of DNase I at 222 nm decreased in the presence of 1-1.4 mM SDS indicating degradation of the secondary structure of DNase I, while DTAC had not effect on the ellipticity at 222 nm, even in the presence of 10 mM DTAC. The enzymatic activity of DNase I was abolished by SDS, the deactivation profile being compatible with the fluorescence decay profile induced by SDS. On the other hand, no deactivation was induced by DTAC.