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

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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)

The role of subcellular alterations in the process of heart failure remains ill-defined. Because contractile performance of failing heart muscle is depressed, possible alterations in the myosin molecule could be of particular relevance. There is increasing evidence that myofibrillar ATPase activity is reduced in congestive heart failure, whereas the findings on myosin ATPase are still controversial. The molecular causes of the reduced activity are currently not known. Because alpha-MHC is present only in small amounts in normal ventricles, a shift in favor of beta-MHC is of minor importance. Also immunohistochemical data on subspecies of beta-MHC seem not to provide an explanation. A new type of myosin heterogeneity was found by optimizing native polyacrylamide gel electrophoresis in the presence of pyrophosphate. Two bands (VA and VB) were observed in ventricles of patients with valvular disease. Because the two bands were detected also in normal hearts of large mammals, the existence of VA/VB cannot be diagnostic of diseased heart. However, the VA/VB ratio was influenced by the hemodynamic load, whereby the fast migrating band (VA) increased with the diastolic and systolic load. Because a relationship with the hemodynamic load was observed only in surgical muscle specimens, it appears that this heterogeneity is prone to post mortem modification. Further work is required to identify the molecular nature of this heterogeneity and to examine the therapeutic potential of a pharmacological modification of the VA/VB ratio.
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PMID:Structural and functional diversity of human ventricular myosin. 138 32

Myosin and creatine kinase were co-immobilized onto Immunodyne films to mimic the behaviour of creatine kinase bound to the M-line of myofilaments. The Mg-ATPase activity of bound myosin was studied by a coupled enzymatic assay, which detects Mg-ADP in the bulk solution by means of pyruvate kinase and lactate dehydrogenase. The competition for Mg-ADP between pyruvate kinase and creatine kinase either free in solution or co-immobilized with myosin was studied at various creatine phosphate concentrations. Bound creatine kinase competed efficiently when present in very low amounts, corresponding to an activity ratio higher than 1:20,000 between creatine kinase and pyruvate kinase and a molar ratio higher than 1:1000 between creatine kinase and myosin. The Mg-ADP produced by myosin ATPase in the vicinity of the film did not diffuse into the bulk solution but, in the presence of creatine phosphate, was recycled into Mg-ATP by the neighbouring creatine kinase. The existence of an unstirred layer near the surface of the film is sufficient to explain the channeling of ADP (or ATP) between co-immobilized myosin and creatine kinase, without direct interaction or 'intimate coupling' between the enzymes. The problem now is to determine the importance of this kind of facilitated diffusion in the myofilaments in vivo.
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PMID:A model system of coupled activity of co-immobilized creatine kinase and myosin. 138 5

A quantitative histochemical technique was developed for determining the kinetics of the calcium-activated myosin ATPase (Ca(2+)-myosin ATPase) reaction in rat skeletal muscle fibres. Using this technique, the maximum velocity (Vmax) and the apparent Michaelis-Menten rate constant for ATP (K(app)) of the Ca(2+)-myosin ATPase reaction were measured in type-identified fibres of the rat medial gastrocnemius (MG) muscle. The Vmax and the K(app) of the Ca(2+)-myosin ATPase reaction were lowest in type I fibres and highest (i.e., approx. two times greater) in type IIb fibres. The K(app) in type IIa fibres was similar to that in type I. However, the Vmax was 1.5 times greater in type IIa fibres, compared to type I fibres. Evidence is presented to suggest that the type IIb fibre population in the MG does not represent a single myosin isozyme. In addition, the broad range of Vmax and K(app) values indicates that there is marked heterogeneity in the myosin heavy chain and myosin light chain composition of myosin isozymes among individual fibres.
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PMID:Quantitative determination of calcium-activated myosin adenosine triphosphatase activity in rat skeletal muscle fibres. 138 25

To investigate the relationship between the mechanical and biochemical properties of cardiac myosin, the sliding velocity of isolated cardiac myosin obtained from both euthyroid and hyperthyroid rabbits on actin cables was measured with an in vitro motility assay system. Ten rabbits (T) were treated with L-thyroxine to induce hyperthyroidism, and eight nontreated animals (N) were used as controls. Myosin was purified from the left ventricles of anesthetized animals. Myosin isozyme content was analyzed by the pyrophosphate gel electrophoresis method, and myosin adenosinetriphosphatase (ATPase) activity was determined on the same sample. Long well-organized actin cables of green algae, Nitellopsis, were used in the in vitro motility assay. Small latex beads were coated with purified cardiac myosin and introduced onto the Nitellopsis actin cables. Active unidirectional movement of the beads on the actin cables was observed under a photomicroscope, and the velocity was measured. The velocity was dependent on ATP concentrations, and the optimal pH for bead movement was approximately 7.0-7.5. The mean velocity was higher in T than in N (0.66 +/- 0.12 vs. 0.32 +/- 0.09 micron/s, P less than 0.01). Both Ca(2+)-activated ATPase activity and the percentage of alpha-myosin heavy chain were also higher in T than in N (0.691 +/- 0.072 vs. 0.335 +/- 0.072 microM Pi.mg-1.min-1, P less than 0.01, and 79 +/- 12 vs. 26 +/- 7%, P less than 0.01, respectively). The velocity of myosin closely correlated with both Ca(+2)-activated myosin ATPase activity (r = 0.87, P less than 0.01) and the percentage of alpha-myosin heavy chain (r = 0.87, P less than 0.01).
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PMID:Sliding velocity of isolated rabbit cardiac myosin correlates with isozyme distribution. 138 92

The adaptation of single fibers in medial gastrocnemius (MG), a fast-twitch extensor, and tibialis anterior (TA), a fast-twitch flexor, was studied after 14 days of spaceflight (COSMOS 2044) or hindlimb suspension. Cross-sectional area (CSA) and succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar adenosinetriphosphatase (ATPase) activities were determined in fibers identified in frozen serial cross sections. Fibers were categorized as light, dark, or intermediate on the basis of myosin ATPase staining and alkaline preincubation and immunohistochemically as reacting with slow, fast, or both slow and fast myosin heavy chain monoclonal antibodies. Because there was a close relationship between these two means of categorizing fibers, all fibers were categorized on the basis of the immunohistochemical reaction. The percentage of slow- and fast-twitch fibers of the MG and TA were unchanged in either group. Mean fiber size of all fibers, irrespective of type, was unaffected in either muscle after flight or suspension. The fibers that expressed both fast and slow myosin heavy chains were smaller than control in the MG of both experimental groups. Compared with control, the SDH and total SDH activities in the MG were significantly less in suspended rats, with the fast-twitch fibers showing the largest difference. The ATPase activity in the MG was higher in flight than in control or suspended rats. There were no significant effects of flight on fibers of the TA. In contrast, the TA in suspended rats had higher GPD activities than either control or flight rats.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Adaptation of fibers in fast-twitch muscles of rats to spaceflight and hindlimb suspension. 138 49

The negatively charged residues in the N-terminus of actin and the 697-707 region on myosin subfragment 1 (S-1), containing the reactive cysteines SH1 and SH2, are known to be important for actin-activated myosin ATPase activity. The relationship between these two sites was first examined by monitoring the rates of SH1 and SH2 modification with N-ethylmaleimide in the presence of actin and, secondly, by testing for direct binding of SH1 peptides to the N-terminal segment on actin. While actin alone protected SH1 from N-ethylmaleimide modification, this effect was abolished by an antibody against the seven N-terminal amino acids on actin, F(ab)(1-7), and was greatly reduced when the charge of acidic residues at actin's N-terminus was altered by carbodiimide coupling of ethylenediamine. Neither F(ab)(1-7) nor ethylenediamine treatment reversed the effect of F-actin on SH2 reactivity in SH1-modified S-1. These results show a communication between the SH1 region on S-1 and actin's N-terminus in the acto-S-1 complex. To test whether such a communication involves the binding of the SH1 site on S-1 to the N-terminal segment of actin, the SH1 peptide IRICRKG-NH2(4+) was used. Cosedimentation experiments revealed the binding of three to six peptides per actin monomer. Peptide binding to actin was affected slightly, if at all, by F(ab)(1-7). The antibody also did not change the polymerization of G-actin by the peptides. The peptides caused a small reduction in the binding of S-1 to actin and did not change the binding of F(ab)(1-7).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Antibody and peptide probes of interactions between the SH1-SH2 region of myosin subfragment 1 and actin's N-terminus. 142 Feb 4

The movement of reconstituted thin filaments over an immobilized surface of thiophosphorylated smooth muscle myosin was examined using an in vitro motility assay. Reconstituted thin filaments contained actin, tropomyosin, and either purified chicken gizzard caldesmon or the purified COOH-terminal actin-binding fragment of caldesmon. Control actin-tropomyosin filaments moved at a velocity of 2.3 +/- 0.5 microns/s. Neither intact caldesmon nor the COOH-terminal fragment, when maintained in the monomeric form by treatment with 10 mM dithiothreitol, had any effect on filament velocity; and yet both were potent inhibitors of actin-activated myosin ATPase activity, indicating that caldesmon primarily inhibits myosin binding as reported by Chalovich et al. (Chalovich, J. M., Hemric, M. E., and Velaz, L. (1990) Ann. N. Y. Acad. Sci. 599, 85-99). Inhibition of filament motion was, however, observed under conditions where cross-linking of caldesmon via disulfide bridges was present. To determine if monomeric caldesmon could "tether" actin filaments to the myosin surface by forming an actin-caldesmon-myosin complex as suggested by Chalovich et al., we looked for caldesmon-dependent filament binding and motility under conditions (80 mM KCl) where filament binding to myosin is weak and motility is not normally seen. At caldesmon concentrations > or = 0.26 microM, actin filament binding was increased and filament motion (2.6 +/- 0.6 microns/s) was observed. The enhanced motility seen with intact caldesmon was not observed with the addition of up to 26 microM COOH-terminal fragment. Moreover, a molar excess of the COOH-terminal fragment competitively reversed the enhanced binding seen with intact caldesmon. These results show that tethering of actin filaments to myosin by the formation of an actin-caldesmon-myosin complex enhanced productive acto-myosin interaction without placing a significant mechanical load on the moving filaments.
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PMID:The effects of smooth muscle caldesmon on actin filament motility. 142 47

Forty-five Large White barrows were injected daily i.m. with either excipient from 30 to 100 kg BW (CTRL), excipient from 30 to 60 and porcine somatotropin (pST; 100 micrograms/kg BW) from 60 to 100 kg BW (pST-60), or pST (100 micrograms/kg BW) from 30 to 100 kg BW (pST-30). Somatotropin accelerated overall growth rate (+4 and +9% for pST-60 and pST-30, respectively), increased longissimus (+10.3 and +14.7%) and semitendinosus (+17 and +13%) muscle weights, and decreased backfat (-49 and -58%) and leaf fat (-49 and -53%) weights. The administration of pST resulted in a similar increase in muscle fiber size for all fiber types in both longissimus (LM) and semispinalis (SS) muscles (+21%). Somatotropin had otherwise little effect on muscle fiber types and biochemical traits of LM, whereas dramatic changes were observed in SS. The relative area occupied by Type IIB fibers was increased (+22 and +29%) and that of Type I fibers was decreased (-10 and -15%). In pST-30 animals, myosin ATPase activity (+15%) and native myosin fast isoform proportion (+10%) were augmented, and energy metabolism was more glycolytic (lactate dehydrogenase: +25%) and less oxidative (citrate synthase: -13%; beta-hydroxyacyl-CoA dehydrogenase: -21%). Compared to CTRL animals, administration of pST increased muscle water concentration (LM: +.8 and +1.1%: SS: +3.3 and +3.3%) and decreased intramuscular fat (LM: -29 and -27%; SS: -39 and -50%). The pH measured 45 min and 24 h postmortem, glycogen content, reflectance, and index of light diffusion were mostly not affected by pST treatment. In conclusion, pST had a very favorable effect on growth performance without any important effect on meat quality traits except for the reduction in intramuscular lipid content. The results indicated that the effects of pST on muscular histochemical and biochemical characteristics were different in LM and SS muscles.
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PMID:Performance, plasma hormones, histochemical and biochemical muscle traits, and meat quality of pigs administered exogenous somatotropin between 30 or 60 kilograms and 100 kilograms body weight. 145

Up to 50% of [35S]-heparin molecules prepared from rat skin bind to rabbit muscle myosin ATPase, in a concentration dependent manner, producing a stable complex with a dissociation constant of 3 x 10(-7) M. The [35S]-heparin in the complex has a distinct electrophoretic behaviour and is precipitated by TCA together with myosin. Other [35S]-glycosaminoglycans, namely, heparan sulfate, dermatan sulfate and chondroitin sulfate also prepared from rat tissues are unable to form complexes with the enzyme. Among the sulfated glycosaminoglycans obtained from different sources only heparin is able to displace the bound [35S]-heparin from the ATPase. Heparin with high affinity for antithrombin III, prepared by antithrombin-affinity chromatography, dislodges up to 90% of the bound [35S]-heparin. Furthermore, antithrombin III-high affinity heparin shows a high affinity for myosin ATPase when compared to antithrombin III-low affinity heparin which shows a low affinity for the enzyme. It is also shown that myosin ATPase inhibits the "in vitro" plasma anticoagulant activity of heparin. These are suggestive that the special structure of the heparin molecules needed for the binding to antithrombin and myosin ATPase bears important similarities. The mechanism of the hemorrhagic effect of heparin is discussed in view of these interactions.
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PMID:Interaction of heparin with myosin ATPase: possible involvement with the hemorrhagic activity and a correlation with antithrombin III high affinity-heparin molecules. 147 Oct 71

Spinal isolation (SI), i.e., the isolation of the lumbar spinal cord via a rostral and a caudal cord transection and bilateral dorsal rhizotomy, was used to determine the effects of chronic (6 months) inactivity on the size and metabolic properties of fibers in the cat soleus. Fibers were classified as dark or light, based on their staining reactions to myosin ATPase, alkaline preincubation, and immunohistochemically as expressing fast and/or slow myosin heavy chains (MHC). Succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) activities were assessed histochemically. Following SI, both the light and the dark ATPase fibers in the SI cats were significantly smaller than the light ATPase fibers in the controls. Normally 100% of the fibers were light ATPase and reacted exclusively with the slow antibody. After SI, approximately 45% of the fibers were dark ATPase fibers, many reacting with both fast and slow MHC antibodies. The total amount and concentration of GPD were higher in the light and dark ATPase fibers in SI compared with light ATPase fibers in controls. In contrast, although the total amount of SDH per fiber was decreased, reflecting the decrease in fiber size, the mean SDH concentration per fiber was unchanged following SI. These data indicate that there is a close coordination in the regulation of GPD activity and the type of myosin. SDH activity, on the other hand, appears to be resistant to decreased levels of activity and unloading, i.e., there seems to be a minimum level of oxidative potential in the soleus that is independent of activity level. Fiber sizes, however, are very sensitive to less-than-normal amounts of neuromuscular activity and/or loading.
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PMID:Enzyme and size profiles in chronically inactive cat soleus muscle fibers. 153 Oct 89


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