Interaction of rat brain microtubule proteins and 6S tubulin with rabbit skeletal muscle actomysin.

The interaction between actomyosin from rabbit skeletal muscle and microtubule proteins or 6S tubulin from rat brain was investigated with respect to the change in ATPase activity and physicochemical properties. Myosin bound to both microtubule proteins and 6S tubulin at low ionic strength. In the aggregates the molar ratio of microtubule proteins or 6S tubulin to myosin was 0.5–1.5 or 1.5–2.5. The superprecipitation of actomyosin was inhibited by 6S tubulin. The degree of superprecipitation inhibition was dependent on the mixing order of myosin, actin, 6S tubulin, and ATP. When myosin was preincubated first with 6S tubulin, the inhibition was most marked. The actin activation of myosin Mg-ATPase was inhibited by both microtubule proteins and 6S tubulin with stronger effects by the latter. The preincubation of myosin with 6S tubulin prior to the addition of actin induced not only greater inhibition of ATPase but also the binding of a larger quantity of 6S tubulin to myosin than the preincubation of myosin with actin. The similar results were obtained with microtubule proteins.