Activation and conformational changes of adenylate kinase in urea solution

The activation and inactivation of adenylate kinase during denaturation in urea are compared with changes in UV absorbance at 287 nm, CD spectrum change at 222 nm, fluorescence intensity of ANS binding and small angle of X ray scattering. At 1 mol/L of urea the enzyme is activated 1.5 fold companied with a subtle decreasing of its second structure, whereas its tertiary structure is fairly resistant to denaturation. By comparing the studies of the crystal structure and the mechanism of the catalysis of adenylate kinase, the activation is believed to result from the effect that low concentration of urea increases the flexibility of the active site of the enzyme. This suggestion was confirmed by the results of the fluorescence intensity changes of ANS binding to adenylate kinase versus the concentration of urea.