Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.6.4.1 (myosin ATPase)
1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Protein phosphorylation may play a critical role in stimulus-coupled secretion of platelets. Some platelet proteins become phosphorylated on exposure to agents such as thrombin and collagen, and the smallest of these phosphoproteins (molecular weight 20,000), has been identified as a light chain of myosin. Phosphorylation of myosin light chain increases the activity of actin-activated myosin ATPase and the resultant contraction of the actomyosin presumably mediates the release reaction. Platelet myosin light chain kinase has been identified as a calcium-dependent enzyme requiring calmodulin for its activity. Calmodulin is a Ca2+-binding protein with a molecular weight of approximately 18,000 which seems to be involved in a wide variety of cellular processes. Although a growing body of evidence suggests that non-muscle actomyosin, such as that isolated from platelets, is regulated by Ca2+-calmodulin-dependent light chain phosphorylation, the precise relationship between the phosphorylation and the function of platelets is not clearly established. We now present pharmacological evidence that a calmodulin-mediated system, such as Ca2+-dependent myosin light chain phosphorylation, also plays an important role in the phenomenon of the release reaction. N-(6-aminohexyl)-5-chloro-1-napthalene-sulphonamide (W-7) (refs 13-15) is shown to bind selectively to calmodulin in vitro and inhibit its biological activity.
...
PMID:Ca2+-calmodulin-dependent phosphorylation and platelet secretion. 743 2

Smooth muscle hypertrophy is often found in tissue subjected to abnormal physical stress. To determine if physical stress (strain) per se could increase the contractile potential of airway smooth muscle (ASM), we compared cultured ASM cells subjected to strain to control cells (no strain) for rates of 1) myosin light chain kinase (MLCK)-mediated myosin light chain (LC20) phosphorylation, 2) actin-activated myosin ATPase, and 3) myosin light chain phosphatase-mediated myosin dephosphorylation. Lysates from strained cells showed increases in both LC20 phosphorylation activity and actomyosin ATPase activity but decreased rates of phosphatase-dependent myosin dephosphorylation. The increased LC20 phosphorylation activity and ATPase activity of the strained cells were accompanied by increases in cellular content of MLCK and myosin, respectively, compared with control. Because the cultured ASM cells exposed to strain expressed higher MLCK activity and actomyosin ATPase activity but lower myosin light chain phosphatase activity, these data suggest that physical stress in part determines ASM potential for contractile state.
...
PMID:Mechanical strain increases contractile enzyme activity in cultured airway smooth muscle cells. 761 41

Although the alkali or essential light chains of skeletal muscle myosin are not required for actin-activated myosin ATPase activity, these myosin subunits are necessary for force transmission with in vitro actin motility assays and are believed to stabilize the alpha-helical neck region of myosin subfragment-1. To probe the functions of the essential light chains during myofibril assembly, we used recombinant DNA procedures to deplete this light chain in cultured muscle. Retroviral expression vectors were constructed which encoded the exon-1 sequence of the myosin light chain-1 gene in antisense orientation. These vectors were applied to myogenic cells from embryonic chick and quail pectoralis muscle. Colonies expressing antisense RNA were selected in growth medium containing the neomycin analogue G-418, plus 5-bromo-2'-deoxyuridine (BrdU) and triggered to differentiate by removal of the latter. Expression of antisense myosin light chain-1 mRNA impaired muscle development. In the antisense cultures there were more mononucleated cells, fewer and smaller myotubes which had poorly developed myofibrils and high levels of diffusely staining myosin heavy chain, not apparent in control myotubes. Protein synthesis in the myotube cultures was analyzed by 35S-methionine labelling and two-dimensional gel electrophoresis. Except for a suppression of approximately 80% of myosin light chain-1f synthesis, the overall pattern of protein synthesis was not altered significantly. These studies suggest that retardation of myosin light chain-1f accumulation inhibits or delays myofibrillogenesis.
...
PMID:Antisense suppression of skeletal muscle myosin light chain-1 biosynthesis impairs myofibrillogenesis in cultured myotubes. 775 4

Ca(2+)-dependent myosin light chain (MLC) phosphorylation is an important step in the initiation of smooth muscle contraction. However, MLC phosphorylation alone cannot account for all aspects of contractile regulation, suggesting the involvement of other elements. In this article we present evidence obtained from Triton X-100 detergent skinned and intact tissue which demonstrates that vascular smooth muscle contraction can be initiated by a Ca(2+)-dependent mechanism that does not require prior MLC phosphorylation. We show that Ca2+ can initiate contractions supported by cytidine triphosphate (CTP) and that these contractions are inhibited by calmodulin antagonists, suggesting a Ca(2+)-calmodulin dependence of force distinct from that for MLC phosphorylation. Evidence is presented to demonstrate that carotid medial fibers contain a mitogen-activated protein (MAP) kinase which is activated by Ca2+ and may catalyze caldesmon phosphorylation. Based in part on our results and those of other investigators, we propose that direct Ca(2+)-calmodulin binding to caldesmon or phosphorylation of caldesmon by a Ca(2+)-dependent MAP kinase disinhibits caldesmon. Disinhibition of caldesmon allows an inherent basal level of actin-activated myosin ATPase activity to be expressed. The result is the slow development of force.
...
PMID:Regulation of vascular smooth muscle contraction: myosin light chain phosphorylation dependent and independent pathways. 776 83

This study determined if phorbol ester-induced contraction of vascular smooth muscle requires calcium-dependent myosin light chain (MLC) phosphorylation and, if not, whether the mechanical characteristics of the contraction in terms of stiffness and crossbridge cycling are similar to those during a calcium- and MLC phosphorylation-dependent contraction. Carotid arterial strips were exposed to 1.0 microM phorbol 12,13-dibutyrate (PDBu) in the presence of normal physiological salt solution (PSS) or after calcium depletion in calcium-free PSS and compared with contraction elicited by calcium-containing 110 mM KCl-PSS. PDBu induced maximal stress in both the presence and absence of calcium. While there was a temporal correlation between MLC phosphorylation and shortening velocity during KCl depolarization, shortening velocity was dissociated from MLC phosphorylation during PDBu stimulation. The stress-stiffness relationship was not different during KCl and PDBu stimulation, suggesting similar crossbridge interactions even though MLC phosphorylation levels were significantly different. These results demonstrate that PDBu-induced contraction of the swine carotid artery is not dependent on calcium or MLC phosphorylation. We suggest the possibility that activation of a calcium-independent PKC isoform may result in the expression of an inherent level of actin-activated myosin ATPase activity resulting in the slow development of stress.
...
PMID:Phorbol ester-induced contractions of swine carotid artery are supported by slowly cycling crossbridges which are not dependent on calcium or myosin light chain phosphorylation. 824 64

Polylysine (10-13 kDa) stimulates contraction in smooth muscle skinned fibers and activates actomyosin adenosinetriphosphatase (ATPase) activity in the absence of myosin light chain phosphorylation [P. T. Szymanski and R. J. Paul. Adv. Exp. Med. 304: 363-368, 1991; P. T. Szymanski, J. D. Strauss, G. Doerman, J. DiSalvo, and R. J. Paul. Am J. Physiol. 262 (Cell Physiol. 31): C1445-C1455, 1992]. To provide further information on the mechanism of polylysine action on contractility in smooth muscle, we investigated its effect on ATPase activity and conformation of purified gizzard myosin. We report here that polylysine directly stimulates myosin ATPase activity in a concentration-dependent manner. This stimulation could be completely abolished with the addition of heparin, a negatively charged heteropolysaccharide. Polylysine (10 microM) increases myosin ATPase activity to a level similar to that of myosin phosphorylation. Addition of 10 microM polylysine to phosphorylated myosin [with myosin light chain kinase and adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), to approximately 1.9 mol P/mol myosin], however, did not further stimulate ATPase activity. At 0.2 M KCl (the salt concentration at which myosin exists primary in the 10S form), the addition of polylysine increases myosin ATPase activity to a level comparable to that of untreated myosin in 0.3 M KCl. These changes parallel the increase in solution viscosity elicited by polylysine. These results suggest that polylysine induces a transition in myosin conformation from the 10S to the 6S form, and this was confirmed by electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Polylysine activates smooth muscle myosin ATPase activity via induction of a 10S to 6S transition. 836 68

1. Using beta-escin and ionomycin-treated skinned smooth muscle strips of the rabbit mesenteric artery, the effects of calyculin A (CL-A, an inhibitor of type 1 and 2A phosphatases) on mechanical activities, phosphorylation of myosin light chain (MLC) and the relationship between the two were studied in Ca(2+)-free solution containing 4 mM EGTA and these effects were compared with those evoked by Ca2+. 2. The threshold concentration of Ca2+ required to increase either tension or MLC-phosphorylation was 0.1 microM and maximum effects were obtained at 10 microM. MLC was mainly monophosphorylated, rather than diphosphorylated, in the presence of Ca2+. ED50 value for Ca2+ was 0.54 microM for either tension or MLC-phosphorylation. The relationship between tension and MLC-phosphorylation is linear in the pCa range 7-5.5. 3. In Ca(2+)-free solution (containing either 20 mM EGTA or 4 mM EGTA with or without 4 mM BAPTA), 3 microM CL-A produced a contraction, the maximum amplitude of which was similar to that evoked by 10 microM Ca2+. CL-A (0.03-3 microM) concentration-dependently increased both tension and MLC-phosphorylation in Ca(2+)-free solution containing 4 mM EGTA. The threshold concentration of CL-A required for the increase in either tension or MLC-phosphorylation was 0.03 microM and maximum effects were obtained at 3 microM. In the presence of CL-A, MLC was not only monophosphorylated but also diphosphorylated. ED50 values for CL-A were 0.39 microM for tension, 0.44 microM for the monophosphorylated form of MLC and 0.54 microM for all phosphorylated (mono + di) forms. The relationship between tension and the monophosphorylated form of MLC was linear over the concentration range studied and was similar to that for Ca2+. 4. H-7 (3 microM, an inhibitor of protein kinase C) inhibited neither the tension nor phosphorylation of MLC induced by 10 microM Ca2+ or 3 microM CL-A. At a high concentration (30 microM), H-7 slightly inhibited both the tension and phosphorylation of MLC induced by either stimulant without a change in the tension-MLC-phosphorylation relationship. KN-62, an inhibitor of Ca(2+)-calmodulin-dependent protein kinase II, did not modify either the tension or the phosphorylation of MLC induced by 10 microM Ca2+ or 3 microM CL-A. CK-II, another inhibitor of Ca(2+)-calmodulin-dependent protein kinase II, did not inhibit the contraction induced by 3 microM CL-A. 5. SM-1 (0.03-0.3 mM) and ML-9 (0.1 and 0.3 mM), inhibitors of MLC-kinase, each lowered the resting level of MLC-phosphorylation in Ca2+-free solution and also inhibited both the tension and MLC-phosphorylation induced by 10 microM Ca2+ or 3 microM CL-A, in a concentration-dependent manner.Neither SM-1 nor ML-9 modified the relationship between tension and either monophosphorylated or all phosphorylated (mono + di) forms of MLC in the presence of Ca2+ or CL-A.6. In a solution containing MgITP (the substrate for myosin ATPase but not for MLC-kinase) with no MgATP, 10 microM Ca2+ failed to produce contraction. Under these conditions, the amplitude of the contraction induced by 3 microM CL-A was greatly diminished in comparison with that induced in the presence of MgATP.7. The present results suggest that in smooth muscle cells of the rabbit mesenteric artery, CL-A in Ca2+-free solution, produces a maximum contraction through an indirect activation of Ca2+-calmodulin independent(constitutively active) MLC-kinase via its inhibitory action on MLC-phosphatases. Based on this evidence, it is hypothesized that, in these cells, a constitutively active MLC-kinase may be present, though its action may be concealed by that of endogenous MLC-phosphatase.
...
PMID:Effects of calyculin A on tension and myosin phosphorylation in skinned smooth muscle of the rabbit mesenteric artery. 839 95

The small GTPase Rho is implicated in physiological functions associated with actin-myosin filaments such as cytokinesis, cell motility, and smooth muscle contraction. We have recently identified and molecularly cloned Rho-associated serine/threonine kinase (Rho-kinase), which is activated by GTP Rho (Matsui, T., Amano, M., Yamamoto, T., Chihara, K., Nakafuku, M., Ito, M., Nakano, T., Okawa, K., Iwamatsu, A., and Kaibuchi, K. (1996) EMBO J. 15, 2208-2216). Here we found that Rho-kinase stoichiometrically phosphorylated myosin light chain (MLC). Peptide mapping and phosphoamino acid analyses revealed that the primary phosphorylation site of MLC by Rho-kinase was Ser-19, which is the site phosphorylated by MLC kinase. Rho-kinase phosphorylated recombinant MLC, whereas it failed to phosphorylate recombinant MLC, which contained Ala substituted for both Thr-18 and Ser-19. We also found that the phosphorylation of MLC by Rho-kinase resulted in the facilitation of the actin activation of myosin ATPase. Thus, it is likely that once Rho is activated, then it can interact with Rho-kinase and activate it. The activated Rho-kinase subsequently phosphorylates MLC. This may partly account for the mechanism by which Rho regulates cytokinesis, cell motility, or smooth muscle contraction.
...
PMID:Phosphorylation and activation of myosin by Rho-associated kinase (Rho-kinase). 870 56

Parturition results from the establishment of phasic regular uterine contractions. Contractility in myometrial smooth muscle is stimulated by an increase in intracellular calcium ([Ca2+i]) which activates myosin light chain phosphorylation leading to increased myosin ATPase activity and enhanced rate of acto-myosin cross bridge formation. G proteins play a pivotal role in smooth muscle activation and relaxation by coupling cell membrane receptors to effector enzymes and ion channels. G alpha(s) and G alpha(i) stimulate and inhibit adenylyl cyclase, respectively and control cAMP formation. G alpha(q) stimulates phospholipase C resulting in the formation of two second messengers: inositol 1,4,5-trisphosphate (InsP3) which releases Ca2+ from the sarcoplasmic reticulum, and 1,2-diacylglycerol which activates protein kinase C. The oxytocin receptor stimulates myometrial contractility by increasing [Ca2+i] through both pertussis toxin resistant (G alpha(q)) and pertussis toxin sensitive (?G alpha (i)) pathways. beta-Adrenoceptors and prostaglandin EP2 receptors promote relaxation via G alpha(s)-adenylyl cyclase. The concentration of myometrial oxytocin receptors is five-times higher in pregnant compared to non-pregnant myometrium but decreases in samples obtained during labour. When myometrial slices are challenged with oxytocin there is a rapid increase in InsP3 levels with a time course which is similar to the rise in [Ca2+i] provoked by oxytocin in cultured myometrial cells. The formation of InsP3 in response to oxytocin in myometrial tissue at term is similar in samples obtained before and after the onset of labour. G alpha(q) and G alpha(i) are expressed at similar levels in non-pregnant and in pregnant myometrium obtained before or during labour. By contract, G alpha(s) levels are higher in pregnant compared to non-pregnant myometrium and decrease in samples obtained during labor. These changes in G alpha(s) are paralleled by prostaglandin E2-induced adenylyl cyclase activity in the same tissues. Parturition may be the consequence of downregulation of pathways that favour uterine quiescence by increasing cAMP formation, resulting in a relative dominance of stimulatory receptors that increase InsP3/Ca2+ availability.
...
PMID:Parturition: activation of stimulatory pathways or loss of uterine quiescence? 871 97

In smooth muscle and specific nonmuscle cells the phosphorylation of the regulatory myosin light chains by myosin light chain kinase (MLCK) is an obligatory step in actin-induced activation of myosin ATPase and subsequent contractile events. We have previously demonstrated that CaM phosphorylated by casein kinase II fails to activate bovine platelet MLCK (Sacks et al. (1992) Biochem. J. 283, 21-24). While myosin light chains are perceived as the only known substrate for MLCK phosphorylation activity, we now show that MLCK phosphorylates CaM. This phosphorylation of CaM is dependent upon the presence of basic peptides such as poly-L-arginine (optimal basic peptide/CaM ratio = 0.08) and is stimulated by saturating [Ca2+] (K0.5 = 16 microM). CaM phosphorylation was inhibited by KT5926, a specific MLCK inhibitor, with a dose-dependency identical to that for inhibition of myosin light chain phosphorylation. Native and MLCK-phosphorylated CaM were indistinguishable in activating MLCK to phosphorylate myosin light chains. Interestingly, MLCK in which the CaM-binding site has been removed is able to phosphorylate CaM in a Ca(2+)-independent manner, suggesting that two CaM molecules bind to intact MLCK simultaneously, one on the inhibitory (pseudosubstrate) domain and one at the catalytic site. CaM phosphorylation by MLCK occurred exclusively on Thr 29 (90%) and Thr 26 (10%) in the first Ca(2+)-binding pocket. In summary, CaM phosphorylation by MLCK differs from CaM phosphorylation catalyzed by other kinases (i.e., the insulin receptor or casein kinase II) in both basic peptide and Ca2+ requirements as well as in the sites of phosphorylation. Further investigations of this model may provide insight into the mechanisms of MLCK activation and substrate recognition.
...
PMID:Phosphorylation of calmodulin in the first calcium-binding pocket by myosin light chain kinase. 880 14


<< Previous 1 2 3 4 5 6 Next >>

---