Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This review summarizes the results obtained by biochemical and physiological studies on the functional implications of the two-headed structure of the myosin molecule. Our nonidentical two-head hypothesis of myosin is supported by biochemical studies on myosin ATPase. The reaction mechanism of the Mg2+-ATPase reaction catalyzed by one head of the myosin molecule is shown to be different from that catalyzed by the other head, and the reaction intermediate, MPADP, is produced in head B but not in head A. Evidence for differences in the chemical structures of the two heads of myosin is also presented. The myosin preparation is shown to be a mixture of homodimers with respect to its g-chain composition, but every homodimer has the non-identical two heads, B and A. Furthermore, the molecular mechanism for acceleration of the Mg2+-ATPase reaction by F-actin and that for its control by Ca2+ ions and Mg2+-ATP are discussed, based on the nonidentical two-head hypothesis of the myosin molecule. It was shown that the formation and decomposition of the key intermediate, A(B)MPADP are required for tension development and shortening. One cycle of ATP hydrolysis by crossbridges synchronously initiated by a rapid stretch or a sudden release of a slow stretch, indicating that the probability of dissociation of a crossbridge by its interaction with ATP depends on its angular position. It is also demonstrated that rotation of the base of nucleoside triphosphate about the glycosyl bond is essential for formation of MPXDP from M2XTP, as well as for muscle contraction. Based on these biochemical and physiological studies on the movement of the myosin head in muscle contraction, a molecular mechanism for muscle contraction is proposed.
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PMID:Functional implications of the two-headed structure of myosin. 16 89

Myosin from chicken pectoralis muscle consists of isozymes that differ in their alkali light chains. It is possible to isolate alkali 1 (A1) and alkali 2 (A2) homodimers of native myosin by immunoadsorption methods, and to compare their steady-state kinetics as well as their assembly into synthetic filaments under a variety of ionic conditions. Bipolar filaments of the isozymes formed at low salt concentrations had a narrow length distribution and did not differ from controls made from unfractionated myosin. Chicken myosin also assembles into highly homogeneous minifilaments similar to those formed by rabbit myosin in a citrate/Tris buffer. Analytical ultracentrifugation and electron microscopy showed that A1-homodimer, A2-homodimer and unfractionated myosin assembled into 0.3 micron short, bipolar minifilaments, which were indistinguishable from one another in size and shape. The steady-state myosin ATPase activity of the two homodimeric isozymes was identical in K+(EDTA) and Ca2+ assay media. The actomyosin Mg2+ ATPase measured at 25 and 55 mM-KCl (pH 8.0) showed only minor differences in both Vmax and Kapp. Actomyosin activity was also determined for the more homogeneous minifilament preparations of the isozymes and these, as well, produced essentially indistinguishable kinetic parameters. Thus we find no evidence to support the hypothesis that a particular alkali light chain of myosin can affect either the structure of the filaments or the steady-state rate of ATP hydrolysis.
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PMID:Assembly and kinetic properties of myosin light chain isozymes from fast skeletal muscle. 622 5

The effects of oxygenation (95% O2 + 5% CO2) and/or SOD (400 mg/l) on addition to St. Thomas' Hospital cardioplegic solution were examined by hemodynamic, cytochemical and biophysical assessments in the isolated working rat heart subjected to hypothermic ischemic arrest (22 degrees C in temperature, 180 min in ischemic time) with multidose cardioplegic infusion. According to the feature of used cardioplegic solution, thirty-two rats were divided into four groups (8 animals per group): That is, Group I; O2 (+) SOD (+), Group II; O2 (-) SOD (+), Group III; O2 (+) SOD (-), Group IV (control); O2 (-), SOD (-). Aortic flow (AF) recovery, expressed as a percent of pre-arrest AF, was 76.7 +/- 11.7% in Group I, 66.9 +/- 7.1% in Group II, 73.9 +/- 11.6% in Group III and 57.7 +/- 12.9% in Group IV (mean +/- SD). Differences in recovery between Group I vs III and Group III vs IV approached statistically significance (respectively, p < 0.01, p < 0.05). The birefringence ratio (ATP value/air value) of the biopsy specimen was 2.49 +/- 0.53 in Group I, 1.96 +/- 0.44 in Group II, 2.04 +/- 0.29 in Group III and 1.65 +/- 0.39 in Group IV (mean +/- SD). Difference between Group I and Group IV indicated statistically significance (p < 0.05). The birefringence ratio (X) had good correlation with the AF recovery ratio (Y): Y = 29.7 + 19.1X (R = 0.74). No statistical difference was seen from cytochemical assessment (myosin ATPase stain) in four groups.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Effects of oxygenation and/or SOD on addition to St. Thomas' Hospital cardioplegic solution]. 847 61

The smooth muscle tropomyosin isoforms beta and gamma were isolated in pure form and labeled with N-(1-pyrenyl)iodoacetamide (PIA) on the cysteine residues at either the N- or the C-terminal region (Cys-36 and Cys-190 of beta- and gamma-isoforms, respectively). The effect of caldesmon (CaD) on local conformational changes in different regions of the tropomyosin molecule was determined on the basis of changes in the excimer fluorescence (excited dimer of pyrene) formed in homodimers of tropomyosin isoforms. In the absence of actin, excimer fluorescence from the pyrene at Cys-190 of gamma-tropomyosin homodimer decreased in a simple manner on the addition of CaD, whereas the excimer from the Cys-36 of beta-tropomyosin homodimer exhibited a biphasic change, suggesting that additional weak binding sites exist near Cys-36. In the presence of actin, CaD-induced changes in the excimer fluorescence of pyrene-tropomyosin were observed only with Cys-36, and this change was associated with an inhibition of actin-activated myosin ATPase. A competition study with unlabeled tropomyosin isoforms indicated that the different excimer changes exhibited by beta- and gamma-tropomyosin in the presence of CaD were due to conformational changes in different regions of the tropomyosin molecule and not to differences in their affinities for CaD. Experiments with recombinant CaD mutants derived using the baculovirus expression system showed that the inhibition of tropomyosin potentiation of actomyosin ATPase by CaD requires the regions between residues 728-756 and 718-727 on the CaD molecule, although the latter region was sufficient for direct interaction with tropomyosin.
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PMID:Inhibition of smooth muscle actomyosin ATPase by caldesmon is associated with caldesmon-induced conformational changes in tropomyosin bound to actin. 852 57

Several works have shown the importance of the creatine kinase (CK) system for cardiac energetics and Ca2+ homeostasis. Nevertheless, CK-deficient mice have cardiac function close to normal, at least under conditions of low or moderate workload. To characterize possible adaptive changes of the sarcoplasmic reticulum (SR) and potential role of glycolytic support in cardiac contractility we used the skinned fibre technique to study properties of the SR and myofibrils, in control and muscle-type homodimer (MM-/mitochondrial-CK)-deficient mice. In control fibres, SR Ca2+ loading with ATP and phosphocreatine (solution PL) was significantly better than loading with ATP alone (solution AL), as determined by analysis of caffeine-induced tension transients. Loading in the presence of ATP and glycolytic intermediates (solution GL) was not significantly different from solution PL. These data indicate that Ca2+ uptake by the SR in situ depends on a local ATP:ADP ratio that is controlled by both CK and glycolytic enzymes. In CK-deficient mice, Ca2+ loading was impaired in solution PL due to the absence of CK. In solution GL, loading was significantly increased, such that calculated Ca2+ release parameters were normalized to those in control fibres in solution PL. In CK-deficient mice, fibre kinetic parameters of tension recovery were impaired after quick stretch in solution PL and were not improved in solution GL. These results show that in CK-deficient mice, at least under basal conditions, glycolysis can replace the CK system in fueling the SR Ca2+ ATPase, but not the myosin ATPase, and may in part explain the limited phenotypic alterations seen in the hearts of these mice.
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PMID:Glycolysis supports calcium uptake by the sarcoplasmic reticulum in skinned ventricular fibres of mice deficient in mitochondrial and cytosolic creatine kinase. 1088 44