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)

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.
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PMID:Diphosphorylation of platelet myosin by myosin light chain kinase. 153 1

The importance of perfusion of the coronary vasculature in the regulation of ATPase activity of myosin in rat myocardial cells has been studied. Quantitative histochemistry was used to determine the activity of the enzyme among cells in tissues that had been either perfused through the coronary system or superfused over the surface of the tissue. Enzymatic activity was measured in cryostatic sections from three different preparations: 1) hearts frozen immediately after removal from the animal; 2) isolated hearts frozen after they had been perfused through the coronary circulation; and 3) isolated papillary muscles or trabeculae that had been superfused after dissection and then frozen. ATPase activity was measured in the isolated tissues at different times after dissection. Both calcium- and actin-activated myosin ATPase activities were uniform among cells in both the ventricles of the hearts frozen immediately after dissection and those that had been perfused through the coronary system. In the superfused tissues, although calcium-activated myosin ATPase activity was uniform, actin-activated ATPase activity was not uniform for about 90 minutes after the dissection, the period required for stabilization of the contraction. The pattern of nonuniformity was complex. In all bundles the lowest enzymatic activity was found in the most superficial cells. In very thin bundles, the cells in the center had the highest activity. In the medium and thicker bundles, there were three concentric zones of actin-activated ATPase activity, the superficial zone with the lowest activity, an intermediate zone with high activity, and a central zone with lower activity. Within each zone, the activity was often greatest in myocardial cells immediately next to blood vessels even though the blood vessels had not been perfused. The transverse distribution of ATPase activity of myosin could be explained by a mechanism in which cells in blood vessels (presumably endothelium) release a substance that upregulates myosin ATPase activity, with the rate of release being related to the local oxygen tension. A downregulating substance may also be produced. The period of stabilization of the contraction coincides with the time during which the pattern of actomyosin ATPase activity is nonuniform. These data suggest that the contractile proteins are regulated by a substance produced by blood vessels in proportion to the local PO2, and possibly in relation to shear force on the vascular endothelium.
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PMID:Contractile proteins in myocardial cells are regulated by factor(s) released by blood vessels. 153 52

L(+)Lactic acid enhances myosin ATPase in vitro. Different organic acids were tested for activation of myosin ATPase activity. L(+)Lactic is more effective in stimulating ATPase than D(-)Lactic. D(+) and L(-)Malic acids were also effective at the concentration of 2.5 x 10(-2)-5.0 x 10(-2) mmoles/l. At 3.0 x 10(-2) mmoles/l concentration the following acids are activators: acetic, oxalic, malonic, oxaloacetic, pyruvic, glyoxylic, glycolic; succinic is an inhibitor and acetoacetic is without effect. The activation is not in relation with the pKa of these acids. The inhibitory effects of organic acids are evident at the concentration of 5.0 x 10(-2) mmoles/l. This inhibitory effect is linearly increasing with their pKa. The results are discussed in connection with the possible role of these metabolites in controlling not only ATPase activity towards splitting of ATP, but also in controlling the removal of its hydrolytic products.
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PMID:Effects of monocarboxylic and dicarboxylic acids on myosin ATPase activity tested by luminometric procedure. 153 14

Inhibition of the myosin subfragment 1 (S-1) ATPase activity by beryllium fluoride was studied directly in the presence of MgATP and following preincubation of samples with MgADP. In both cases, the rates of inhibition were very slow, with kapp = 0.5 and 58 M-1 s-1, respectively, in analogy to the rates of inhibition of myosin ATPase by vanadate [Goodno, C. C. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 2620-2624]. The very different rates of inhibition in the presence of MgATP and on preincubation with MgADP suggested that beryllium fluoride binds to the M.ADP state of myosin. The slow inhibition rates and the nonlinear dependence of the observed rates on beryllium fluoride concentration were consistent with a two-step inhibition process involving a rapid binding equilibrium to yield a collisional complex, M.ADP.BeF3-, and its slow isomerization into M++.ADP.BeF3-. A third, much slower, step was required to account for the conversion of the stable M++.ADP.BeF3- to a virtually irreversibly inhibited complex. Kinetic description of the inhibition pathway was derived from the observed rates of inhibition of myosin ATPase, information on the binding of beryllium fluoride to M.ADP, and measurements of epsilon ADP chase from M++.epsilon ADP.BeF3-. The isomerization rate and equilibrium constants were 1.4 x 10(-2) s-1 and 50, respectively, and the overall binding constant of beryllium fluoride to M.ADP was 5 x 10(5) M-1. The inhibitory complex showed a 16% enhancement to tryptophan fluorescence of S-1 and a reduced quenching of epsilon ADP by acrylamide. It is concluded that M++.ADP.BeF3- is analogous to the M++.ADP.Vi and M**.ADP.Pi states of myosin.
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PMID:Inhibition of myosin ATPase by beryllium fluoride. 153 58

A spectrophotometric method for the measurement of inorganic phosphate (P(i)) has been developed by using 2-amino-6-mercapto-7-methylpurine ribonucleoside and purine-nucleoside phosphorylase (purine-nucleoside:orthophosphate ribosyltransferase, EC 2.4.2.1). This substrate gives an absorbance increase at 360 nm on phosphorolysis at pH 6.5-8.5, and at pH 7.6 the change in extinction coefficient is 11,000 M-1.cm-1. The Michaelis-Menten constants of the two substrates with the enzyme are 70 microM for the nucleoside and 26 microM for P(i); the kcat is 40 s-1 (25 degrees C). The assay was shown to quantitate P(i) in solution at concentrations at least down to 2 microM. It can be used to measure the kinetics of P(i) release from phosphatases, such as GTPases and ATPases, by coupling the two enzymic reactions. The utility of this assay was shown by three test systems: glycerol kinase plus D-glyceraldehyde acting as an ATPase and actin-activated myosin ATPase, and myosin subfragment 1, hydrolyzing a single turnover of ATP, releasing P(i) with a rate constant the same as the steady-state ATPase activity.
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PMID:A continuous spectrophotometric assay for inorganic phosphate and for measuring phosphate release kinetics in biological systems. 153 9

Hypertrophy of the urinary bladder was produced in rabbit by partial ligation of the urethra. Electrophoresis of the bladder smooth muscle myosin on highly porous (3.5-7% gradient) SDS-polyacrylamide gel revealed two heavy chain isoforms, SM-1 and SM-2 with approximate molecular weights of 204,000 and 200,000, respectively. The ratio of the SM-2 to SM-1 heavy chain is 3:1 for myosin isolated from normal bladder smooth muscle, and this ratio changes to about 1:1 in hypertrophied bladder. Despite a change in the ratio of SM-2 to SM-1, the myosin ATPase and the actin-activated ATPase activities are not altered in response to hypertrophy.
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PMID:Smooth muscle myosin isoform distribution and myosin ATPase in hypertrophied urinary bladder. 153 95

The articularis humeri (AH) muscle of the horse is a small muscle composed of histochemically identified type I and IIA extrafusal fibers and a large number of muscle spindles. A total of 150 complete spindles with both spindle poles available were examined in serial transverse sections. On the basis of myosin ATPase-staining reactions after alkaline and acid preincubations, four types of intrafusal fibers, namely, bag1, bag2, "mixed" bag, and chain fibers, were identified. A high proportion of the spindle population (62.6%) consisted of multiple-bag spindles containing three or more (up to six) bag fibers. Also one-bag-fiber spindles were observed. The one-bag-fiber spindles containing a bag2 fiber could be traced into tandem linkages. "Mixed" bag intrafusal fibers, differing in their ATPase staining profile at the two poles, were found in spindles containing also at least one bag1 and one bag2 fiber. An unusually long extracapsular tract (up to 5,500 microns) of the bag intrafusal fibers was observed.
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PMID:High incidence of multiple-bag fiber muscle spindles in the articularis humeri muscle of the horse. 154 62

One of the fundamental properties of cardiac muscle is the increase in force generated and work performed with a rise in the resting length of the tissue. There are data to indicate that length-dependent responses of electromechanical coupling and calcium binding by troponin are part of the basis for the pressure-volume relation in the heart. In this study, the contribution of changes in the functional properties of the contractile proteins independent of modification in electromechanical coupling has been examined. Isolated working hearts containing either a mixture of myosin heavy chain (MHC) isozymes (alpha[fast] and beta [slow]) or exclusively the fast MHC have been subjected to left atrial filling pressures (LAPs) between 5 and 20 cm H2O. After 40 minutes at a given LAP, the heart was quickly frozen. The relative activities of calcium- and actin-activated ATPase of V1 and V3 myosin, containing alpha- and beta-MHC, were measured in cryostatic sections of the heart by quantitative histochemistry under conditions for which the concentration of calcium would not be limiting. In hearts containing both isozymes of myosin, the relative enzymatic activity of each isozyme of myosin varied with LAP. At low LAP, V1 was primarily responsible for the enzymatic activity, but as LAP increased the relative contribution of V1 decreased and that of V3 increased. The change in the calcium- and actin-activated activities of the enzyme with change in LAP occurred within 5 minutes and was reversible. In spite of the apparent substitution of enzymatic activity of V3 for V1, total myosin ATPase activity did not decline, but instead remained constant.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of left atrial filling pressure on the activity of specific myosin isozymes in rat heart. 164 32

The purpose of this study was to determine if selected biochemical parameters representing the contractile and calcium regulating systems of cardiac muscle scaled among mammals having inherently different resting heart rates (RHR). Eight mammalian species with RHR ranging from 51 to 475 beats per minute (bpm) were studied. The oxidative capacity of the myocardium is highly correlated with the RHR. The hypothesis of the present study was that the capacities of the energy utilizing processes of contraction and calcium regulation would also be correlated to the functional demand imposed on the muscle as represented by the RHR. Myosin (M) and myofibrillar (MF) ATPase activities, myosin isoenzyme distribution and sarcoplasmic reticulum (SR) ATPase activity were determined. Animals with RHR above 300 bpm express V1 myosin while animals with lower RHR express primarily V3. M and MF ATPase activities correlated with RHR, but the major difference in activities occurred at the 'threshold' RHR of about 300 bpm at which the switch from V3 to V1 appears to occur. SR ATPase activity per mg of microsomal protein was for the most part constant among different mammals, but the SR ATPase activity per g of heart tissue was significantly correlated with RHR as slower beating hearts tended to yield less SR protein per unit mass. We conclude that both the contractile and calcium regulating systems are scaled to the functional parameter of RHR among different mammals. The contractile system uses a slow myosin ATPase isoform at low resting heart rates whereas above the postulated threshold RHR of about 300 bpm a switch in gene expression to a fast myosin ATPase isoform occurs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Contractile and calcium regulating capacities of myocardia of different sized mammals scale with resting heart rate. 165 10

Myosin ATPase activity was measured, by continuous luminometric method, in presence of different molecular weight heparins. ATPase activity decreases in the presence of heparin, when simultaneous incubation with ATP is carried out; the percentage of inhibition is proportional to polysaccharide concentration. Heparins of different molecular weights (1.75 KD to 11.6 KD) are competitive inhibitors of enzymatic activity; the inhibitory effects is also appreciable with trisulphated disaccharide. The possible mechanisms of interaction between heparin and myosin ATPase are discussed.
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PMID:Competitive inhibition of myosin ATPase activity by different molecular weight heparins. 165 81


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