Calcium Regulation in Clam Foot Muscle Calcium Sensitivity of Clam Foot Myosin

Abstract

1. The ATPase activity of clam foot myosin alone in the presence of 10 mM MgCl2 was activated approximately ten-fold by 10 muM free calcium ions. The calcium activation was observed in various concentrations of KCl (35-600 mM) and ATO (1 muM-1 mM), and at various pHs (pH 6-9.4). 2. The superprecipitation and ATPase activities of clam foot myosin B were studied by conducting experiments in two different ways. In one of these, the ATP concentration was varied at a fixed concentration of MgCl2, and in the other, the MgCl2 concentration was varied at a fixed concentration of ATP. The following was found: (a) The activities responded in a biphasic manner to change in either the ATP or MgCl2 concentration, giving a peak activity around 10 muM ATP or MgCl2. It is thus suggested that Mg-ATP complex is responsible for both activation and inhibition in the biphasic response. (b) When the ATP or MgCl2 concentration was higher than 100-300 muM, practically no superprecipitation occurred in either the presence or absence of calcium, whereas the ATPase activity was still strongly activated by calcium. 3. Similar results to those described above (a, b) were obtained by using rabbit skeletal actoclam foot myosin in place of clam foot myosin B. Moreover, it was found that as the ATP concentration increased from 1 muM to 1 mM, Mg-ATPase activity of clam foot myosin in the presence of calcium increased in a monophasic manner and that it was as active as actomyosin in the presence of calcium when the ATP concentration was higher than approximately 200 muM. In other words, actin-activation of myosin-ATPase was absent in the ATP concentration where no superprecipitation of actomyosin was observed. 4. Clam foot myosin contained two types of light chain subunits: LCl (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 calcium sensitivity of actomyosin-ATPase. 5. In our previous report (J. Biochem. 85, 1543-1546, 1979), it was shown that removal of LC1 from clam foot myosin also resulted in loss of the superprecipitation activity of actomyosin reconstituted from "EDTA-washed" myosin. We now provide further evidence that removal of the regulatory light chain (LC1) results in a reversible uncoupling of ATPase reaction from superprecipitation reaction.

Invertebrate muscles: Thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle

“…A large number of papers deal with isolation and initial characterization (e.g., Ca ++ and ATP dependence, heavy and light chain complement) of molluscan actomyosin (Lajtha, 1947;Humphrey, 1948Humphrey, , 1949Weber, 1953;Matsumoto, 1954, 1957;Weber and Portzehl, 1954;de Villafranca, 1955;Tonomura et al, 1955Tonomura et al, , 1956Bailey, 1956;Strelina et al, 1957;Matsumoto, 1957;Maruyama, 1957bMaruyama, , 1958aMatsumoto, 1958aMatsumoto, -d, 1959Kishimoto, 1961;Bárány and Bárány, 1966;Schädler, 1967;Mognoni and Lanzavecchia, 1969;Twarog and Muneoka, 1972;Horie et al, 1975;Azuma et al, 1975;Azuma, 1976;Nishita, 1977;Nishita et al, 1977Nishita et al, , 1979Tsuchiya et al, 1978b-d;Asada et al, 1979;Toyo-Oka, 1979;Tanaka and Tanaka, 1979a,b;Ashiba et al, 1980Ashiba et al, , 1982Kimura et al, 1980;Asakawa, 1980;Stephenson and Williams, 1980;Morita and Kondo, 1982;Szent-Györgyi and Niebieski, 1982;Yoshitomi and Konno, 1982;Krause and Munson, 1982;Kodama and Konno, 1983...…”

Kinetic trapping of intermediates of the scallop heavy meromyosin adenosine triphosphatase reaction revealed by formycin nucleotides

“…The finding that the essential light chain of vertebrate smooth-muscle myosin extends to the active site is obviously pertinent to this mechanism (Okamoto et at., 1986). However, the regulatory light chains are vital to this communication, since their removal results in permanent activation of both the actin-activated (Kendrick-Jones et al, 1976) and the intrinsic myosin ATPase (Ashiba et al, 1980;Jackson et at., 1987). The heavy chain itself is also important, since cleavage at the neck region to yield SI or labelling of the reactive thiol group prevents communication ( Fig.…”

Amino acid sequence of myosin essential light chain from the scallop Aquipecten irradians

“…0006-2960/86/0425-7651S01.50/0 tentatively located in an extended "linker region", creases during contraction (Hardwicke et al, 1983). The change is apparently due to the movement of SELC (Hardwicke & Szent-Gyórgyi, 1985) and takes place on myosin in the absence of actin (Ashiba et al, 1980;Wells & Bagshaw, 1985). SRLC protects SELC from digestion by papain (Stafford et al, 1979) and abolishes the reactivity of the thiol groups of SELC (Hardwicke et al, 1982).…”