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)

70 human hearts were studied less than 36 hours after death. The apex, and in some cases other parts of the myocardium were homogenized, DNA, hydroxyproline content, myofibrillar Ca2+ and Mg2+ ATPase were measured. In normal hearts the DNA and collagen content were 372 +/- 9 mg and 36 +/- 7 mg. Ca2+ and Mg2+ ATPase of the myofibrils prepared from these hearts have shown the same specific activity (35 +/- 5 and 34 +/- 6 nmol/min./mg) as those from fresh biopsies taken during open-chest surgery. The heart weight correlates with the DNA content (r= + 0.58 -p less than 0.01) and with the myofibrillar ATPase (r= - 0.33 - p less than 0.02) but not with the DNA concentration nor with the collagen content or concentration. The main result of this study was the presence of a negative correlation between the DNA content of the heart and the Mg2+ or Ca2+ myofibrillar ATPase (r= - 0.31, p less than 0.05 - r= - 0.45, p less than 0.01). This correlation was analysed with reference to the histological and biochemical studies published by several authors in human or experimental heart hypertrophy and it was suggested that in human heart hypertrophy the decrease of the myofibrillar or myosin ATPase is a direct consequence of the high degree of polyploidy of the muscular cells observed in this condition.
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PMID:Myofibrillar ATPase, DNA and hydroxyproline content of human hypertrophied heart. 13 Feb 42

In experimental cardiac hypertrophy induced by aortic constriction of rats, the hypertrophy was established after 5-7 days. The basic biochemical changes for increasing tissue mass; increases in protein, nucleic acid, and polyamine synthesis started to occur between 2 and 8 hours followed by an increase in uridine nucleotide pools via predominance of "salvage" pathway. Although the precise coupling mechanism between mechanical stress and biochemical changes is still obscure, an interval between increased load and DNA transcription may be quite short. Some of the key enzymes regulating these processes showed a biphasic response the reason of which is not clear. The established hypertrophied heart muscle showed a decrease in velocity of isotonic shortening and an increase in resting tension. The former alteration is referred to a decrease in myosin ATPase activity and an disorder in excitation-contraction coupling mechanism, and the latter is supposed to be due to an increase in collagen in heart muscle.
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PMID:Biochemical aspects of experimental cardiac hypertrophy. 13 28

Re-innervated extensor digitorum longus, soleus and plantaris muscles of the rat were studied after denervation performed at various postnatal ages. The muscle fibres, which normally run from tendon to tendon as independent units, were found to be very frequently connected by myomuscular junctions, both in the form of terminal insertions of one fibre into another and of lateral bridges which may join two or more muscle fibres at one or more levels. Positive reaction for AChE activity was demonstrated at the level of the junctions. Incubation for myosin ATPase activity showed that myomuscular junctions are only found between fibres of the same histochemical type, which in re-innervated muscles are usually aggregated in 'type groupings'. Ultrastructural features were similar in both forms of myomuscular junctions. The appearance is that of an interdigitation of muscle projections from neighbouring fibres, each projection being covered by a basement membrane with attached collagen fibrils. The finger-like projections at their endings contain vesicles and elongated cisternae filled with granular dense material. It is postulated that the synchronous activity of neighbouring fibres within the compact motor units of reinnervated muscles is a causal factor initiating the formation of myomuscular junctions.
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PMID:Myomuscular junctions in re-innervated rat skeletal muscle. 14 21

To study the diastolic properties of the heart includes examining active relaxation, passive ventricular stiffness and atrial contraction. (i) The main determinant of active relaxation is the adenosine triphosphate (ATP) concentration. Relaxation needs to occur so that the ATP content of the cell can be decreased by activation of the myosin ATPase, which in turn depends upon an intracellular messenger, elevation of the calcium transient. In a model of cardiac hypertrophy active relaxation is always slower. This slowing accompanies a slowing of the calcium transient, a diminution in the activity of the Na+/Ca2+ exchanger, a change in the properties of Na+, K+ ATPase and a decreased concentration of Ca2+ ATPase in the sarcoplasmic reticulum. (ii) Chamber stiffness is likely to be increased only in relation to the degree of ventricular hypertrophy. The main, if not unique, determinant of ventricular diastolic tissue stiffness is the structure and concentration of the collagen. Consequently tissue stiffness is augmented in cardiac hypertrophy in which the ventricular collagen concentration is elevated. It is important that both clinically and experimentally cases of cardiac hypertrophy, even those resulting from pressure overload in which myocardial stiffness and cardiac collagen concentration remain unchanged, have been documented. A good example of this is the DOCA-salt model of arterial hypertension. (iii) Atrial contraction is normally more rapid than ventricular contraction, the biological basis for which is the difference in isomyosin content.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Biological basis of diastolic dysfunction of the hypertensive heart. 139 55

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.
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PMID:Demonstration of a direct role for myosin light chain kinase in fibroblast-populated collagen lattice contraction. 184 33

To test the possibility that ATP diffusion limits the kinetics of myosin ATPase (EC. 3.6.1.3) in situ, myosin was covalently bound to the surface of 2 kinds of films: collagen and Immunodyne. On collagen films, it was bound either with 1-ethyl-3 (3 dimethyl-aminopropyl)carbodiimide (EDC) or with dimethyl-3,3'-dithiobis(propionimidate) (DTP). The apparent Km for K+-ATP rose from 0.26 mM for free myosin in solution to 2-5 mM for covalently bound myosin, and maximum K+-ATPase activity was very low. With the other film, Immunodyne from Pall, the maximum activity of bound myosin was 170 nmol per min per 1.5 cm2 film. The apparent Km for K+-ATP was 2.1 mM when the incubation mixture was vigorously stirred, and the effect of stirring indicated that the kinetics of K+-ATP hydrolysis are limited by external diffusion. The large amount of myosin bound per unit of Immunodyne film surface permitted the study of Mg2+-ATPase activity, although it was 400-500 times less than the K+-ATPase activity. The apparently non-Michaelian kinetics of Mg2+-ATP hydrolysis are attributable to the external diffusion. The apparent Michaelis constant observed at low Mg2+-ATP concentrations rose from 0.27 microM for myosin in solution to 5 microM for myosin bound to Immunodyne film.
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PMID:Diffusion-limited kinetics of immobilized myosin ATPase. 252 82

In this study we examined morphological and structural aspects of aponeurotic fragments from one patient with Dupuytren and Marfan diseases. Our purpose was to evaluate if characteristic features of Dupuytren aponeurosis are in some way influenced by alterations in collagenic and elastic bundles present in Marfan syndrome. So we compared histological, enzymatic and immunochemical features of tissue fragments from Marfan with similar fragments from simple Dupuytren patients. We observed a substantial difference in the predominant type of collagen which is adult type I in the normal Dupuytren disease and fetal type III in Marfan patient. Collagenic bundles are more dispersed in Marfan, and the whole aponeurosis seems less compact and resistant. No difference was observed in cellular populations of aponeurosis, and also myofibroblasts are present with abundant myosin ATPase activity both in Marfan with Dupuytren both in Dupuytren alone.
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PMID:[Morphologic and hist-enzymatic aspects of palmar aponeurosis in a patient with Marfan syndrome associated with Dupuytren's contracture]. 262 43

We measured the interrelationships between ventricular muscle myosin mass, myosin ATPase activity and collagen in cats with varying degrees of hypertrophy from left ventricular (LV) pressure-overload produced by either aortic banding or renal hypertension. In order to compare two models of LV pressure-overload with different time courses of progression, the results were analyzed as a function of LV mass or LV weight/body weight (LV/BW) ratio. Myosin was quantitated by SDS-polyacrylamide gel electrophoresis and hydroxyproline was measured as an index of collagen. Myosin concentration was positively correlated with increasing LV mass in control cats. However, in pressure-overloaded LV, myosin concentration was elevated and nearly constant for LV less than 9.0 g, but decreased in LV greater than 9.0 g. Myosin concentration in pressure-overloaded LV was greatest before a significant increase in LV/BW ratio. Hydroxyproline concentration was inversely related to myosin concentration in both LV pressure-overload models and increased with the severity of hypertrophy. Actomyosin ATPase activity in pressure-overloaded LV, was not significantly different from control over a wide range of LV/BW ratios. However, absolute myosin ATP hydrolysis in pressure-overloaded LV, increased by as much as 40%, relative to control, due primarily to increased myosin. The changing spectrum and interrelationships of myosin and collagen were independent of the mechanism of pressure-overload, but were correlated with the severity of hypertrophy.
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PMID:Myocardial changes during the progression of left ventricular pressure-overload by renal hypertension or aortic constriction: myosin, myosin ATPase and collagen. 295 26

Peritubular cells from 15- and 25-day-old rat testis trapped in collagen lattices caused those lattices to contract. Contraction proceeded more rapidly and to a greater extent using cells from younger rats. When 36,000 cells from 15- and 25-day-old rats were trapped in 800 mm2 lattices, the areas were reduced to 28 mm2 and 170 mm2, respectively, within 24 h. The cells from older rats were less effective at contracting the lattice than cells from younger rats. Cytochalasin B (5 micrograms ml-1) inhibited lattice contraction and caused disruption of actin filaments as seen by fluorescent staining with Rh-phalloidin. Cholera toxin (10 micrograms ml-1), and 1 mM-dibutyryl cAMP inhibited lattice contraction, as did 10 microM-trifluoperazine, commonly an inhibitor of calmodulin. The total intracellular concentration of cAMP was greater in peritubular cells from 25-day-old rats than in those from 15-day-old rats: 427 +/- 34 and 120 +/- 16 pmol mg-1 cell protein, respectively. When peritubular cells in monolayer were permeabilized with glycerol, the addition of ATP caused the cells to contract. Cell contraction was greater in cells from 15-day-old rats than 25-day-old rats. When cells were grown on silicone rubber, they caused that surface to wrinkle. Peritubular cells from 15-day-old rats caused the onset of wrinkling at 4 h. At the same time, no wrinkling was observed with cells from 25-day-old rats. Studies of lattice contraction and cell contraction were also made using cells from 20-day-old rats. In each case, contraction was intermediate between that of cells from 15-and 25-day-old rats. The possibility exists that lattice contraction, cell contraction and wrinkling of silicone film result from a mechanism of actin filament sliding, generated by myosin ATPase activity, and is inhibited by cAMP. The reduced rate of contraction in cells from 25-day-old rats may be related to their higher intracellular levels of cAMP. Evidence exists to show that cAMP blocks myosin ATPase activity by inhibiting the phosphorylation of its regulatory peptide, myosin light chain.
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PMID:Contraction of collagen lattice by peritubular cells from rat testis. 302 30

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.
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PMID:Ca2+-calmodulin-dependent phosphorylation and platelet secretion. 743 2


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