Kamiya S, Yoshitomi B, Konno K, Watanabe S
J Biochem. 1985 Jul;98(1):149-56. doi: 10.1093/oxfordjournals.jbchem.a135253.
Heavy meromyosin (HMM) and subfragment-1 (S1) were obtained from squid mantle myosin by tryptic digestion and chymotryptic digestion, respectively. Squid HMM(T) and S1(CT) preparations contained stoichiometric amounts of the two types of light chain subunit; regulatory light chain, LC-2, and essential light chain, LC-1. No difference was detected in the chymotryptic digestibilities of squid mantle myosin in Ca-medium and in EDTA-medium. This is in contrast to the digestibility of scallop adductor myosin. The Mg-ATPase activity of HMM(T) alone and that of acto-HMM(T) were both sensitive to calcium ions. In contrast, the activity of S1(CT) alone and that of acto-S1(CT) were both insensitive to calcium ions. The affinity of HMM(T) for actin was not affected by calcium ions, but the amount of HMM(T) bound to actin was increased by calcium ions from 20% to 60% of the total amount of HMM(T). On the other hand, the actin affinity of S1(CT) and the amount of S1(CT) bound to actin were both unaffected by calcium ions. The role of calcium ions in the regulation of contraction in molluscan muscles is discussed.
重酶解肌球蛋白（HMM）和亚片段-1（S1）分别通过胰蛋白酶消化和糜蛋白酶消化从鱿鱼外套膜肌球蛋白中获得。鱿鱼HMM（T）和S1（CT）制剂含有化学计量的两种类型的轻链亚基；调节轻链LC-2和必需轻链LC-1。在钙介质和EDTA介质中，未检测到鱿鱼外套膜肌球蛋白的糜蛋白酶消化率有差异。这与扇贝闭壳肌肌球蛋白的消化率形成对比。单独的HMM（T）和肌动蛋白-HMM（T）的Mg-ATP酶活性均对钙离子敏感。相比之下，单独的S1（CT）和肌动蛋白-S1（CT）的活性均对钙离子不敏感。HMM（T）对肌动蛋白的亲和力不受钙离子影响，但与肌动蛋白结合的HMM（T）量因钙离子而从HMM（T）总量的20%增加到60%。另一方面，S1（CT）对肌动蛋白的亲和力以及与肌动蛋白结合的S1（CT）量均不受钙离子影响。本文讨论了钙离子在软体动物肌肉收缩调节中的作用。
