スルメイカ外套膜筋のH-メロミオシンとサブフラグメント-1のCa感受性

概要

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H-meromyosin (NMM) and subfragment-1 (S-1) were prepared from squid myosin by digestion with trypsin, chymotrypsin or papain. The chymotryptic and papain HMM and S-1 maintained intact regulatory light chain (R-LC), whereas R-LC in tryptic HMM and S-1 was slightly degraded. As far as pH, KCI and temperature dependencies of Ca-, EDTA-, and Mg-ATPase activities are concerned, these HMM and S-1 preparations were virtually identical with native squid myosin. Squid HMM AND S-1 showed a significant difference in Ca-sensitivity; the Mg-ATPase activity of S-1 was insensitive to Ca, whereas the activity of HMM was very sensitive. Furthermore, the addition of F-actin to HMM and S-1 did not change the Ca-sensitivity of Mg-ATPase. Double reciprocal plots of the actin-activated Mg-ATPase against free actin concentration indicated that the affinity of HMM to actin is unaffected by Ca by the maximal activity is distinctly increased by Ca. On the other hand, both the affinity of S-1 to actin and the maximal activity of acto-S-1 were unaffected by Ca. These results confirmed that the primary role of RLC is to inhibit Mg-ATPase activity of myosin and not to inhibit actin-myosin binding. R-LC is supposed to lose biological functions when S-1 is derived from squid myosin.