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

Myosin was purified from rabbit alveolar macrophages in a form that could not be activated by actin. This myosin could be phosphorylated by an endogenous myosin light chain kinase, up to 2 mol of phosphate being incorporated/mol of myosin. The site phosphorylated was located on the 20,000-dalton myosin light chain. Phosphorylation of macrophage myosin was found to be necessary for actin activation of myosin ATPase activity. Moreover, the actin-activated ATPase activity was found to vary directly with the extent of myosin phosphorylation, maximal phosphorylation (2 mol of Pi/mol of myosin) resulting in an actin-activated MgATPase activity of approximately 200 nmol of Pi/mg of myosin/min at 37 degrees C. These results establish that phosphyoyration of the 20,000-dalton light chain of myosin is sufficient to regulate the actin-activated ATPase activity of macrophage myosin.
 ...
PMID:Macrophage myosin. Regulation of actin-activated ATPase, activity by phosphorylation of the 20,000-dalton light chain. 15 17

Myosin isolated under phosphorylation conditions, showed an additional band of phosphorylated light chain. In the case of cardiac myosin, LC2 is the phosphorylated light chain whereas in skeletal myosin, it is the 18,000 dalton component known as DTNB light chain. There are no differences in K+-EDTA and Ca2+ activated myosin ATPase of cardiac and skeletal of control and phosphorylated myosins. Our experiments showed that the rat heart and skeletal muscle myosins isolated under phosphorylating conditions exhibited high phosphate content which is associated with higher actin activated Mg2+ ATPase activity of myosin as compared to control. Control myosin phosphorylated using myosin light chain kinase and Ca2+ also showed high actin activated myosin ATPase activity. Beef heart myosin isolated in the presence of phosphate buffer, also exhibited a higher level of phosphate followed by an increase in actin activation as compared to myosin isolated in the absence of phosphate buffer. All these experimental data suggest that there is a direct relationship between actin activation and the amount of phosphate incorporated as a result of phosphorylation.
 ...
PMID:Phosphorylation and its effects on ATPase activity of cardiac and skeletal myosins. 16 48

Recently, one of the authors (K.I.) and other investigators reported that myosin light chain (MLC) of smooth muscle (gizzard, arterial and tracheal) was diphosphorylated by myosin light chain kinase (MLCK) and that diphosphorylated myosin showed a marked increase in the actin-activated myosin ATPase activity in vitro and ex vivo. In this study, we prepared myosin, actin, tropomyosin (human platelet), MLCK (chicken gizzard) and calmodulin (bovine brain) and demonstrated diphosphorylation of MLC of platelet by MLCK in vitro. Our results are as follows. (1) Platelet MLC was diphosphorylated by a relatively high concentration (greater than 20 micrograms/ml) of MLCK in vitro. As a result of diphosphorylation, the actin-activated myosin ATPase activity was increased 3 to 4-fold as compared to the monophosphorylation. (2) Both di- and monophosphorylation reactions showed similar Ca2+, KCl, MgCl2-dependence. Maximal reaction was seen at [Ca2+] greater than 10(-6) M, 60 mM KCl and 2 mM MgCl2. This condition was physiological in activated platelets. (3) Di- and monophosphorylated myosin showed similar Ca2+, KCl-dependence of ATPase activity but distinct MgCl2-dependence. Diphosphorylated myosin showed maximal ATPase activity at 2 mM MgCl2 and monophosphorylated myosin showed a maximum at 10 mM MgCl2. (4) The addition of tropomyosin stimulated actin-activated ATPase activity in both di- and monophosphorylated myosin to the same degree. (5) ML-9, a relatively specific inhibitor of MLCK, inhibited the aggregation of human platelets induced by thrombin ex vivo in a dose-dependent manner. Moreover, this drug also partially inhibited both di- and monophosphorylation reactions and actin-activated ATPase activity. On the other hand, H-7, a synthetic inhibitor of protein kinase C, had little effect on the aggregation of human platelets induced by thrombin ex vivo. From these results, we conclude that diphosphorylation of platelet myosin by MLCK may play an important role in activated platelets in vivo.
 ...
PMID:Diphosphorylation of platelet myosin by myosin light chain kinase. 153 1

The regulatory domain of smooth muscle myosin light chain kinase (MLCK) was studied using monoclonal antibodies. Of the 22 monoclonal antibodies tested, a monoclonal antibody designated LKH-18 was found to activate MLCK in the absence of Ca2+/calmodulin. This activation was even greater when an Fab fragment of LKH-18 was used. Consequently, the actin-dependent smooth muscle myosin ATPase activity and the superprecipitation of actomyosin were significantly activated by MLCK plus LKH-18, even in the absence of Ca2+/calmodulin. The antibody-binding site was studied using proteolytic fragments and synthetic peptide analogues of MLCK. Immunoblot analysis revealed that LKH-18 reacted with the 66 kDa calmodulin-dependent active fragment but not with the 64 kDa inactive fragment or with the 61 kDa calmodulin-independent active fragment. Furthermore, LKH-18 reacted with MLCK-(796-815)-peptide but not with MLCK-(786-801)-peptide or with MLCK-(796-807)-peptide. Therefore the LKH-18-binding site was assigned to amino acid residues 808-815 of MLCK, which are thought to be a part of the calmodulin-binding site. The present results suggest that the binding of ligand to this region induces a conformation change in MLCK and that this abolishes the action of the inhibitory region which exists next to the N-terminal side of the calmodulin-binding site.
 ...
PMID:Activation of smooth muscle myosin light chain kinase activity by a monoclonal antibody which recognizes the calmodulin-binding region. 171 Jan 6

Chicken gizzard actomyosin, containing the calmodulin-myosin light chain kinase (MLCK) system, was incubated in the presence of various concentrations of PSK, a protein-bound polysaccharide from Basidiomycetes, together with Ca2+ and Mg-ATP. The phosphorylation of myosin was enhanced half-maximally by 10-4 g/ml of PSK. However, a similar concentration of PSK reduced the Mg-ATPase activity of the actomyosin. The former was brought about through stimulation of the MLCK activity and the latter through inhibition of the myosin ATPase activity.
 ...
PMID:A protein-bound polysaccharide from Basidiomycetes enhances myosin phosphorylation but inhibits myosin ATPase activity: studies with a crude actomyosin preparation of chicken gizzard smooth muscle. 183 24

Hypoxic relaxation of norepinephrine contractions of isolated rabbit aorta is rapid, whereas relaxation of KCl contractions is slower and blunted. The data given here suggest that with receptor-evoked contractions of rabbit aorta, the energy-limitation of ATP-dependent K+ channels and other sarcolemmal channels, myosin light chain kinase, and actin-activated myosin ATPase are probably not involved in oxidative energy-contraction coupling. The data strongly support the hypothesis that the rate limiting, energy-dependent step is upstream to myosin light chain kinase, which is 50% inhibited at an ATP concentration of about 0.5 mM. This energy-dependent step may be in the inositol phospholipid transduction system, as we have previously postulated (Coburn et al., 1988). In contrast the energy-limited reaction during KCl contractions appears to be the actin-activated myosin ATPase which is 50% inhibited at a mean ATP concentration of about 0.1 mM.
 ...
PMID:Mechanical and biochemical events during hypoxia-induced relaxations of rabbit aorta. 183 85

Mixing feed fibroblasts with soluble collagen and serum-supplemented culture medium at 37 degrees C results in the entrapment of cells within the polymerizing collagen matrix. This cellular-collagen complex is referred to as a fibroblast-populated collagen lattice (FPCL). In time, this FPCL undergoes a reduction in size called lattice contraction. The proposed mechanism for lattice contraction is cellular force produced by cytoplasmic microfilaments which organize collagen fibrils compacting the matrix. When the regulatory subunits of myosin, myosin light chains, are phosphorylated by myosin light chain kinase (MLCK), myosin ATPase activity is increased and actin-myosin dynamic filament sliding occurs. Elevated levels of myosin ATPase are required for maximal lattice contraction. Cholera toxin inhibits lattice contraction by increasing intracellular levels of cAMP. It is proposed that increased cytoplasmic concentrations of cAMP promote phosphorylation of MLCK, the enzyme important for maximizing myosin ATPase activity. Phosphorylating MLCK in vitro inhibits activity by decreasing its sensitivity to calcium-calmodulin complex. A decrease in MLCK activity would result in lower levels of myosin ATPase activity. MLCK, purified from turkey gizzard, was subjected to limited proteolytic digestion to produce calmodulin-independent-MLCK. The partially digested kinase does not require calcium-calmodulin for activation. Independent-MLCK is not subject to inhibition by phosphorylation. The electroporetic inoculation of independent-MLCK into fibroblasts before FPCL manufacture produced enhanced lattice contraction. Lattice contraction, in the presence of cholera toxin, was restored to normal levels by the prior electroporetic introduction of independent-MLCK. These findings support the hypothesis that increases in cAMP hinder lattice contraction by a mechanism involving inhibition of MLCK and myosin ATPase.
 ...
PMID:Demonstration of a direct role for myosin light chain kinase in fibroblast-populated collagen lattice contraction. 184 33

1. Two types of myosins with phosphorylated and dephosphorylated myosin light chains were prepared from Drosophila flies. The former had ATPase (Ca2(+)- and Mg2(+)-activited) activities twice those of the latter. 2. The myosin phosphorylated with crude myosin light chain kinase from flies showed ATPase (Ca2(+)- and Mg2(+)-activated) activaties twice those of the dephosphorylated myosin. 3. It is suggested that phosphorylation of myosin light chains several hours after emergence stimulates myosin ATPase activity so as to facilitate the flight function of the fruitfly.
 ...
PMID:Regulation of Drosophila myosin ATPase activity by phosphorylation of myosin light chains--I. Wild-type fly. 213 97

The addition of large amounts of myosin light chain kinase to the reconstituted gizzard actomyosin shows diphosphorylation of 20 kDa myosin light chain. Accompanying diphosphorylation, the actin-activated myosin ATPase activity was also enhanced. The extent of diphosphorylation and the myosin ATPase activity were clearly demonstrated to be in a linear relationship. From the time course experiment, the conversion of monophosphorylated light chain into one which was diphosphorylated seemed to be a sequential process. Moreover, analyzing phospho-amino acid by using a two-dimensional electrophoresis technique revealed that monophosphorylated light chain contained phosphoserine and diphosphorylated one contained phosphothreonine in addition to phosphoserine.
 ...
PMID:Linear relationship between diphosphorylation of 20 kDa light chain of gizzard myosin and the actin-activated myosin ATPase activity. 293 11

Actomyosin in smooth muscle is in a quiescent state. The mechanism or mechanisms by which Ca2+ activates the actomyosin ATPase is not clear. There is sufficient evidence for the presence of enzyme systems which phosphorylate and dephosphorylate myosin light chains. The activity of the kinase that phosphorylates the myosin is regulated by cAMP-dependent protein kinase. Phosphorylated kinase has decreased affinity for calmodulin and lower activity when compared with unphosphorylated myosin light chain kinase. The activity of myosin light chain kinase is also regulated by calcium-calmodulin. In the presence of Ca2+, myosin is phosphorylated. In the absence of Ca2+, the phosphatase activity becomes dominant; the myosin remains in the unphosphorylated form under this condition. The Mg2+-ATPase of the phosphorylated myosin is activated by actin. The maximal activation of the Mg2+-ATPase by actin requires Ca2+ and tropomyosin, a protein located on the thin filament. Hence, the actin-activation of the Mg2+-ATPase requires Ca2+ even after phosphorylation by the calcium-calmodulin dependent kinase. The regulation of actin-activated ATPase activity by myosin light chain phosphorylation is depicted in the schematic diagram. Caldesmon, an actin-binding protein which also binds to calmodulin in the presence of Ca2+, has been shown to be present in thin-filaments isolated from smooth muscle. This protein inhibits actin-activated myosin ATPase activity. The release from this inhibition requires Ca2+ and calmodulin. The possibility that caldesmon is also involved in the calcium regulation of actomyosin in smooth muscle is presently under investigation in a number of laboratories.
 ...
PMID:Regulation of actomyosin ATPase in smooth muscle. 294 44


1 2 3 4 5 Next >>