Effects of Tubulin-myosin Interaction on Guanosine-5'-Triphosphate Hydrolysis by Myosin

概要

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Tubulin from porcine brain inhibited not only the Mg-ATPase activity but also the Mg-GTPase activity of actomyosin from rabbit skeletal muscle. The inhibitory effect of tubulin on GTPase, however, was weak and a large amount of tubulin was necessary for half-maximum inhibition as compared with ATPase inhibition by tubulin. Although tubulin inhibited GTP hydrolysis by actomyosin at higher concentrations of GTP, it was found that tubulin conversely accelerated the hydrolysis of GTP at low concentrations of substrate (<0.3mM). The Km value for GTP fell from 2.5×10^<-3> to 1.1×10^<-3>M upon adding tubulin. Since tubulin slightly activated myosin Mg-GTPase activity, it might block the site of actin activation. The inhibition did not seem to be competitive, because excess actin did not completely eliminate the GTPase inhibition by tubulin. The addition of KCl (at 50-100 mM) activated the GTPase activity of actomyosin, but this activation was not observed when tubulin was present. Further addition of KCl (at 200-400 mM) decreased the GTPase activity both in the presence and absence of tubulin, although the GTPase activity in the presence of tubulin was higher than that in the absence of tubulin. The extent of inhibition of GTPase by tubulin was not significantly affected by the presence of colchicine or vinblastine.
公益社団法人日本薬学会の論文
1981-09-25