CALCIUM REGULATION IN CLAM FOOT MUSCLE - CALCIUM SENSITIVITY OF CLAM FOOT MYOSIN
CALCIUM REGULATION IN CLAM FOOT MUSCLE - CALCIUM SENSITIVITY OF CLAM FOOT MYOSIN
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DOI：
10.1093/oxfordjournals.jbchem.a133038
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发表时间：
1980-01-01
影响因子：
2.7
通讯作者：
WATANABE, S
中科院分区：
文献类型：
--
作者：
ASHIBA, G;ASADA, T;WATANABE, S
The ATPase activity of clam foot myosin alone in the presence of 10 mM MgCl2 was activated approximately 10-fold by 10 .mu.M free Ca ions. The Ca activation was observed in various concentrations of KCl (35-600 mM) and ATP (1 .mu.M-1 mM), and at various pHs (pH 6-9.4). The superprecipitation and ATPase activities of clam foot myosin B were studied in 2 different ways. In one of these the ATP concentration was varied at a fixed concentration of MgCl2; in the other the MgCl2 concentration was varied at a fixed concentration of ATP. The activities responded in a biphasic manner to change in either the ATP or MgCl2 concentration, giving a peak activity around 10 .mu.M ATP or MgCl2. Mg-ATP complex is responsible for both activation and inhibition in the biphasic response. When the ATP or MgCl2 concentration was higher than 100-300 .mu.M, practically no superprecipitation occurred in either the presence or absence of Ca; the ATPase activity was still strongly activated by Ca. Similar results to those described above were obtained by using rabbit skeletal actoclam foot myosin in place of clam foot myosin B. As the ATP concentration increased from 1 mM to 1 mM, Ag-ATPase activity of clam foot myosin in the presence of Ca increased in a monophasic manner. It was as active as actomyosin in the presence of Ca when the ATP concentration was higher than approximately 200 .mu.M. Actin-activation of myosin-ATPase was absent in the ATP concentration where no superprecipitation of actomyosin was observed. Clam foot myosin contained 2 types of light chain subunits: LC1 (17,000 daltons) and LC2 (16,000 daltons). Only LC1 was removed upon washing clam myosin with 10 mM EDTA, and removal of LC1 resulted in loss of the Ca sensitivity of actomyosin-ATPase. Removal of LC1 from clam foot myosin resulted in loss of the superprecipitation activity of actomyosin reconstituted from EDTA-washed myosin. Removal of the regulatory light chain (LC1) results in a reversible uncoupling of ATPase reaction from superprecipitation reaction.
