Abstract
To study the effects of urea on the denaturation of myosin B prepared from smooth dogfish, myosin B was kept at 20°C for 10 min with various concentrations (0-3.0M) of urea, and the reduced viscosity was measured as a parameter for structural changes in myosin B. The decrease in the reduced viscosity of myosin B containing urea above 1.0M was similar to that of myosin in the presence of urea, However, the reduced viscosity of F-actin was slightly affected by urea even above 1.0M.
The reduced viscosity of myosin B did not recovered to its initial level through the removal of urea at concentrations above 1.0M urea, but that of myosin recovered perfectly through the re-moval of urea at concentrations up to 3.0M urea. In the presence of urea above 1.0M, myosin B irreversibly dissociated into myosin and actin. Therefore, it is concluded that the urea denaturation of myosin B would be attributed to its dissociation into myosin and actin as well as the conforma-tional changes of myosin molecules in the presence of urea above 1.0M. Accordingly, shark myosin B is fairly stable under physiological concentrations of urea below 1.0M.
