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)

We define conditions under which the two C-terminal residues of actin, Cys-374 and Phe-375, can be selectively removed by proteolysis with trypsin. This modification had little effect on the secondary structure of actin detected by Fourier-transform infrared spectroscopy. However, removing these residues caused small but significant decreases in the critical concentration of actin, in its ability to activate myosin ATPase, and in its interaction with tropomyosin and troponin. Removing residues 374-375 caused dramatic changes in the actin filament as seen by electron microscopy. The filaments had a much greater and more irregular curvature and were intertwined into disordered multifilament bundles. Removing 374-375 also significantly lowered the flow viscosity of filamentous-actin solutions. These data suggest an increase in the flexibility and fragility of the filament, supporting the idea that the C-terminus forms one of the major intermonomer contacts in the filament.
 ...
PMID:Removing the two C-terminal residues of actin affects the filament structure. 173 27

Growing rats and adult weight-stable mice bearing a transplantable methylcholanthrene-induced sarcoma were compared with animals with various states of malnutrition. Heart protein synthesis was measured in vivo. Myocardial RNA, myofibrillar protein composition and the Ca2+-activated ATPase activity in heavy chains of native myosin were measured. 'Fingerprints' were made from myosin by trypsin treatment to evaluate possible structural changes in the protein. Cardiac protein-synthesis rate was decreased by 20% in growing tumour-bearing rats, by 35% in protein-malnourished (rats) and by 47% in starved rats, compared with freely fed controls (P less than 0.05). Adult tumour-bearing mice showed no significant decrease in myocardial protein synthesis. Pair-weighed control mice had significantly depressed heart protein synthesis. Protein translational efficiency was maintained in both tumour-bearing rats and mice, but was decreased in several groups of malnourished control animals. The Ca2+-activated myosin ATPase activity was decreased in all groups of malnourished animals, including tumour-bearing mice and rats, without any evidence of a change in cardiac isomyosin composition. We conclude that loss of cardiac muscle mass in tumour disease is communicated by both depressed synthesis and increased degradation largely owing to anorexia and host malnutrition. Increased adrenergic sensitivity in hearts from tumour-bearing and malnourished animals is not communicated by increased Ca2+-activated ATPase activity. This may be down-regulated in all groups with malnutrition, without any observable alterations in the isomyosin profile.
 ...
PMID:Protein synthesis, myosin ATPase activity and myofibrillar protein composition in hearts from tumour-bearing rats and mice. 248 44

Myosin (opaque myosin) isolated from the opaque portion of scallop smooth muscle, a catch muscle, was subjected to limited digestion by trypsin during the steady-state ATPase reaction. The 200-kDa heavy chain of opaque myosin was cleaved into 125- and 74-kDa fragments. The proteolytic rate in the absence of Ca2+ was lower than that in the presence of Ca2+, and was similar to that in the presence of ADP and absence of Ca2+. The results suggest that the steady-state intermediate of opaque myosin ATPase in the absence of Ca2+ is EADP, which is consistent with the previous results based on the difference UV-absorption spectrum (Takahashi, M., Sohma, H., & Morita, F. (1988) J. Biochem. 104, 102-107). In the presence of F-actin, the proteolytic rates were decreased, but the digestive patterns by trypsin were similar to those of myosin alone. Even in the presence of F-actin, the proteolytic rate during the ATPase reaction in the absence of Ca2+ was lower than that in the presence of Ca2+, and was similar to that in the presence of ADP and absence of Ca2+. In addition, there was another trypsin-susceptible site which is probably located at 18 kDa from the N-terminal of the heavy chain. The site in the absence of Ca2+ was hardly cleaved when ATP or ADP was present. Similar tendencies were observed even in the presence of F-actin. These findings suggest that the intermediate of opaque myosin ATPase at the steady state in the absence of Ca2+ is EADP even in the presence of F-actin.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Myosin may stay in EADP species during the catch contraction in scallop smooth muscle. 261 94

Modification of Tyr-69 with tetranitromethane impairs the polymerizability of actin in accordance with the previous report [Lehrer, S. S. and Elzinga, M. (1972) Fed. Proc. 31, 502]. Phalloidin induces this chemically modified actin to form the same characteristic helical thread-like structure as normal F-actin. The filaments bind myosin heads and activate the myosin ATPase activity as effectively as normal F-actin. When a dansyl group is introduced at the same point [Chantler, P. D. and Gratzer, W. B. (1975) Eur. J. Biochem. 60, 67-72], phalloidin still induces the polymerization. The filaments bind myosin heads and activate the myosin ATPase activity. These results indicate that Tyr-69 is not directly involved in either an actin-actin binding site or the myosin binding site on actin. Moreover, the results suggest that phalloidin binds to actin monomer in the presence of salt and its binding induces a conformational change in actin which is essential for polymerization, or that actin monomer fluctuates between in unpolymerizable and polymerizable form while phalloidin binds to actin only in the polymerizable form and its binding locks the conformation which causes the irreversible polymerization of actin. Modification of Tyr-53 with 5-diazonium-(1H)tetrazole blocks actin polymerization [Bender, N., Fasold, H., Kenmoku, A., Middelhoff, G. and Volk, K. E. (1976) Eur. J. Biochem. 64, 215-218]. Phalloidin is unable to induce the polymerization of this modified actin nor does it bind to it. Phalloidin does not induce the polymerization of the trypsin-digested actin core. These results indicate that the site at which phalloidin binds is involved in polymerization and the probable conformational change involved in polymerization may be modulated through this site.
 ...
PMID:Interaction of phalloidin with chemically modified actin. 295 2

In order to gain some information regarding Ca2+-dependent ATPase, the enzyme was purified from cardiac sarcolemma and its properties were compared with Ca2+-ATPase activity of myosin purified from rat heart. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by Ca2+ but the maximal activation of Ca2+-dependent ATPase required 4 mM Ca2+ whereas that of myosin ATPase required 10 mM Ca2+. These ATPases were also activated by other divalent cations in the order of Ca2+ greater than Mn2+ greater than Sr2+ greater than Br2+ greater than Mg2+; however, there was a marked difference in the pattern of their activation by these cations. Unlike the myosin ATPase, the ATP hydrolysis by Ca2+-dependent ATPase was not activated by actin. The pH optima of Ca2+-dependent ATPase and myosin ATPase were 9.5 and 6.5 respectively. Na+ markedly inhibited Ca2+-dependent ATPase but had no effect on the myosin ATPase activity. N-ethylmaleimide inhibited Ca2+-dependent ATPase more than myosin ATPase whereas the inhibitory effect of vanadate was more on myosin ATPase than Ca2+-dependent ATPase. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by K-EDTA and NH4-EDTA. When myofibrils were treated with trypsin and passed through columns similar to those used for purifying Ca2+-ATPase from sarcolemma, an enzyme with ATPase activity was obtained. This myofibrillar ATPase was maximally activated at 3-4 mM Ca2+ and 3 to 4 mM ATP like sarcolemmal Ca2+-dependent ATPase. K+ stimulated both ATPase activities in the absence of Ca2+ and inhibited in the presence of Ca2+. Both enzymes were inhibited by Na+, Mg2+, La3+, and azide similarly. However, Ca2+ ATPase from myofibrils showed three peptide bands in SDS polyacrylamide gel electrophoresis whereas Ca2+ ATPase from sarcolemma contained only two bands. Sarcolemmal Ca2+-ATPase had two affinity sites for ATP (0.012 mM and 0.23 mM) while myofibrillar Ca2+-ATPase had only one affinity site (0.34 mM). Myofibrillar Ca2+-ATPase was more sensitive to maleic anhydride and iodoacetamide than sarcolemmal Ca2+-ATPase. These observations suggest that Ca2+-dependent ATPase may be a myosin like protein in the heart sarcolemma and is unlikely to be a tryptic fragment of myosin present in the myofibrils.
 ...
PMID:A comparative study of the rat heart sarcolemmal Ca2+-dependent ATPase and myosin ATPase. 296 55

To obtain information about the adenine recognition site in myosin ATPase, ribosemodified fluorescent analogs of ATP, 3'-O-anthraniloyl and 3'-O-(N-methylanthraniloyl) derivatives, were directly cross-linked to myosin subfragment-1 (S-1) ATPase by irradiation with visible light in the presence of FMN as a photosensitizer. The cross-linking of the fluorescent nucleotides was inhibited by addition of ATP or ADP. Tryptic digestion of the cross-linked S-1 revealed that fluorescence of the analog was associated predominantly with the 50K fragment and its precursor, the 75K one, and slightly with the 20K fragment. However, fluorescence was scarcely associated with the 26K fragment. The results were confirmed by cross-linking experiments using trypsin-split S-1, which mainly consists of the 50K, 26K, and 20K fragments. These findings suggest that the adenine recognition site of the myosin ATPase is located predominantly on the 50K domain.
 ...
PMID:Photosensitized direct cross-linking of fluorescent analogs of ATP to the adenine recognition domain in myosin ATPase. 315 47

The heavy chains of Acanthamoeba myosins. IA, IB and II, turkey gizzard myosin, and rabbit skeletal muscle myosin subfragment-1 were specifically labeled by radioactive ATP, ADP, and UTP, each of which is a substrate or product of myosin ATPase activity, when irradiated with UV light at 0 degrees C. With UTP, as much as 0.45 mol/mol of Acanthamoeba myosin IA heavy chain and 1 mol/mol of turkey gizzard myosin heavy chain was incorporated. Evidence that the ligands were associated with the catalytic site included the observations that reaction occurred only with nucleotides that are substrates or products of the ATPase activity; that the reaction was blocked by pyrophosphate which is an inhibitor of the ATPase activity; that ATP was bound as ADP; and that label was probably restricted to a single peptide following limited subtilisin proteolysis of labeled Acanthamoeba myosin IA heavy chain and extensive cleavage with CNBr and trypsin of labeled turkey gizzard myosin heavy chain.
 ...
PMID:Direct photoaffinity labeling by nucleotides of the apparent catalytic site on the heavy chains of smooth muscle and Acanthamoeba myosins. 745 49

Reactive oxygen species (ROS) have been reported to alter cardiac myofibrillar function as well as myofibrillar enzymes such as myosin ATPase and creatine kinase (CK). To understand their precise mode and site of action in myofibrils, the effects of the xanthine/xanthine oxidase (X/XO) system or of hydrogen peroxide (H2O2) have been studied in the presence and in the absence of phosphocreatine (PCr) in Triton X-100-treated cardiac fibers. We found that xanthine oxidase (XO), with or without xanthine, induced a decrease in maximal Ca(2+)-activated tension. We attributed this effect to the high contaminating proteolytic activity in commercial XO preparations, since it could be prevented a protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), and it could be mimicked by trypsin. In further experiments, XO was pre-treated with 1 mmo1/L PMSF. Superoxide anion production by the X/XO system, characterized by electron paramagnetic resonance spin-trapping technique, was not altered by PMSF. A slight increase in maximal force was then observed either with X/XO (100 mumol/L per 30 mIU/mL) or H2O2. pMgATP-rigor tension relationships have been established in the presence and in the absence of PCr to separate the effects of ROS on myosin ATPase and myofibrillar-bound CK. In the absence of PCr, pMgATP50, the pMgATP necessary to induce half-maximal rigor tension, was reduced from 5.03 +/- 0.17 (n = 21) to 4.22 +/- 0.22 (n = 4) after 25 minutes of incubation in the presence one of 30 mIU/mL. XO and 100 mumol/L xanthine or to 4.04 +/- 0.1 (n = 11) after incubation in the presence of 2.5 mmol/L H2O2. The ROS effects were partially prevented or antagonized by 1 mmol/L dithiothreitol. No effect was observed on pMgATP50 when PCr was absent. pCa-tension relationships have been evaluated to assess the effects of ROS on active tension development. Incubations with H2O2 induced on increase in Ca2+ sensitivity and resting tension when MgATP was provided through myofibrillar CK (PCr and MgADP as substrates) but not when MgATP was added directly. These results suggest that myofibrillar CK was inhibited by ROS. Active stiffness and the time constant of tension changes after quick stretches applied to the fibers were dose-dependently increased by H2O2 only in the presence of PCr. In addition, myofibrillar CK but not myosin ATPase enzymatic activity was depressed after incubation with either ROS. These results suggest that ROS mainly alters CK in myofibrils, probably by the oxidation of its essential sulfhydryl groups. Such CK inactivation results in a decrease in the intramyofibrillar ATP-to-ADP ratio. The effects of ROS on cytosolic and bound CKs may take part in the overall process of myocardial stunning after cardiac ischemia and reperfusion.
 ...
PMID:Creatine kinase is the main target of reactive oxygen species in cardiac myofibrils. 863 32

Cell traction force (CTF) plays a critical role in controlling cell shape, permitting cell motility, and maintaining cellular homeostasis in many biological processes such as angiogenesis, development, wound healing, and cancer metastasis. Calponin is an actin filament-associated cytoskeletal protein in smooth muscles and multiple types of non-muscle cells. An established biochemical function of calponin is the inhibition of myosin ATPase in smooth muscle cells. Vertebrates have three calponin isoforms. Among them, calponin 2 is expressed in epithelial cells, endothelial cells, macrophages, myoblasts, and fibroblasts and plays a role in regulating cytoskeleton activities such as cell adhesion, migration, and cytokinesis. Knockout (KO) of the gene encoding calponin 2 (Cnn2) in mice increased cell motility, suggesting a function of calponin 2 in modulating CTF. In this study, we examined fibroblasts isolated from Cnn2 KO and wild-type (WT) mice using CTF microscopy. Primary mouse fibroblasts were cultured on polyacrylamide gel substrates embedded with fluorescent beads to measure root-mean-square traction, total strain energy, and net contractile movement. The results showed that calponin 2-null fibroblasts exhibit traction force greater than that of WT cells. Adherent calponin 2-null fibroblasts de-adhered faster than the WT control during mild trypsin treatment, consistent with an increased CTF. Blebbistatin, an inhibitor of myosin II ATPase, is more effective upon an alteration in cell morphology when calponin 2 is present in WT fibroblasts than that on Cnn2 KO cells, indicating their additive effects in inhibiting myosin motor activity. The novel finding that calponin 2 regulates myosin-dependent CTF in non-muscle cells demonstrates a mechanism for controlling cell motility-based functions.
 ...
PMID:Deletion of Calponin 2 in Mouse Fibroblasts Increases Myosin II-Dependent Cell Traction Force. 2773 37