Purealin Enhances the Actin-activated ATPase Activity of Myosin, Heavy Meromyosin and Subfragment 1 by Increasing Their Apparent Affinities for Actin

摘要

Purealin, a bromotyrosine derivative isolated from a sea sponge, modulates various types of ATPase activities of the motor proteins including muscle myosins and dynein. But the structural basis of the modulation has been elusive. Here we examined the effect of purealin on the kinetics of actin-activated ATPase activity of rabbit skeletal myosin and explored the possible purealin-induced structural change in the myosin head. The actin-activated ATPase activities of myosin, heavy meromyosin (HMM) and myosin subfragment1(SI) were enhanced to 150, 170, and 130% of the control values by purealin at15, 25 and12 ^M, respectively. The compound decreased the Kapp (actin concentration required to achieve1/2 Vmax) of the actin-activated ATPase of myosin, HMM, and SI, without changing the maximum rates, Vmax, of three enzymes. On the other hand, purealin weakly decreased the ATPase activities in the absence of F-actin. Purealin had no effect on the size of the initial burst of Pi liberation and the ATP-induced increase in intrinsic Tip fluorescence of HMM. However, purealin decreased the intensity of extrinsic fluorescence of SI labeled with 5-(iodoacetamido)fluorescein (lAF) to the reactive thiol, SHI. These results accord with the notion that the conformational change induced by purealin in the myosin head, modifies the affinity between myosin and actin, resulting in the increase in the actin-activated ATPase of myosin.