The catalytic activity and physical properties of bovine thrombin in the presence of dimethyl sulfoxide.
Dimethyl sulfoxide produces an opposite effect on the esterase and amidase activities of bovine thrombin. The esterase activity is increased by two fold but the amidase activity is decreased to 9% of the initial activity in 20% dimethyl sulfoxide. The stimulation of the esterase activity is due to the change in Vmax rather than Km for the substrate p-Tosyl-L-Arginine methyl ester. The inhibition of the esterase activity of thrombin by NaCl is not affected due to the addition of dimethyl sulfoxide. Ki for NaCl, 0.03 M, is the same for both in the absence and in the presence of 10% dimethyl sulfoxide. The catalytic activity of thrombin is inhibited by heparin. This effect is significantly decreased by dimethyl sulfoxide. The dissociation constant of heparin-thrombin complex, measured in the absence and in the presence of 10% dimethyl sulfoxide are 4 nM and 28 nM respectively. Thermal stability of thrombin, determined by monitoring catalytic activity, is increased in the presence of dimethyl sulfoxide. The enhancement of the fluorescence intensity of thrombin in the presence of dimethyl sulfoxide reflects the contribution of more exposed tryptophanyl residues. The alteration of the conformation of the enzyme structure due to the perturbation of the aqueous medium by dimethyl sulfoxide, has been attributed to these observed effects.