Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The contractile properties of cardiac muscle cells are determined by the molecular composition of the contractile apparatus and in particular by the structure of myosin. Three isoforms of myosin heavy chains have been recently identified in the mammalian heart: alpha and beta myosin heavy chains, present in atrial and ventricular myocardium, and nodal myosin heavy chain, present in sino-atrial and atrio-ventricular nodes. The alpha and beta isoforms are coded by two distinct genes whose expression is tissue and developmental stage-specific, and can be regulated by hormonal and mechanical factors. The relative concentration of the two isoforms is correlated with the maximal velocity of shortening and with the energy cost of force generation. In hyperthyroid myocardium the predominant isoform is the alpha, high ATPase myosin heavy chain and the contraction is fast but less economical; in hypothyroid and in mechanically overloaded myocardium the beta, low ATPase isoform is predominant and the contraction is slower and more economical.
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PMID:[Cardiac myosins and myocardial contraction]. 294 27

Limited proteolysis was used to identify regions on the heavy chains of calf thymus myosin which may be involved in ATP and actin binding. Assignments of the various proteolytic fragments to different parts of the myosin heavy chain were based on solubility, gel filtration, electron microscopy, and binding of 32P-labeled regulatory light chains. Chymotrypsin rapidly cleaved within the head of thymus myosin to give a 70,000-dalton N-terminal fragment and a 140,000-dalton C-terminal fragment. These two fragments did not dissociate under nondenaturing conditions. Cleavage within the myosin tail to give heavy meromyosin occurred more slowly. Cleavage at the site 70,000 daltons from the N-terminus of the heavy chain caused about a 30-fold decrease in the actin concentration required to achieve half-maximal stimulation of the magnesium-adenosinetriphosphatase (Mg-ATPase) activity of unphosphorylated thymus myosin. The actin-activated ATPase activity of this digested myosin was only slightly affected by light chain phosphorylation. Actin inhibited the cleavage at this site by chymotrypsin. In the presence of ATP, chymotrypsin rapidly cleaved the thymus myosin heavy chain at an additional site about 4000 daltons from the N-terminus. Cleavage at this site caused a 2-fold increase in the ethylenediaminetetraacetic acid-ATPase activity and 3-fold decreases in the Ca2+- and Mg-ATPase activities of thymus myosin. Thus, cleavage at the N-terminus of thymus myosin was affected by ATP, and this cleavage altered ATPase activity. Papain cleaved the thymus myosin heavy chain about 94,000 daltons from the N-terminus to give subfragment 1.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of proteolysis on the adenosinetriphosphatase activities of thymus myosin. 295 19

We have established a quick method for preparing Physarum myosins whose actin-activated ATPase activities are inhibited by microM levels of Ca2+ (from plasmodial stage: Kohama, K. & Kendrick-Jones, J. (1986) J. Biochem. 99, 1433-1446; and from amoebal stage: Kohama, K., Takano-Ohmuro, H., Tanaka, T., Yamaguchi, Y., & Kohama, T. (1986) J. Biol. Chem. 261, 8022-8027). N-Ethylmaleimide alkylates sulfhydryl (SH) groups on the heavy chains in the heads of the plasmodial myosin. The actin-activated ATPase activity of the modified myosin was significantly decreased when assayed in low Ca2+ concentrations. Moreover, the activity remained low even when the Ca2+ concentrations was increased, i.e., the myosin was desensitized. For complete desensitization, about 4 mol SH per mol myosin (500,000 Mr) must be modified. These residues are probably the "reactive thiols" which have been predicted from primary structure studies to be conserved among myosins of higher and lower eukaryotes. Ultraviolet absorption spectra of the modified and intact myosins showed a peak at 277 nm. The height of this peak in intact myosin was reduced when the Ca2+ concentration was increased. This Ca-induced reduction was hardly detectable in the modified myosin although Ca-binding activity to myosin did not appear to be affected by the modification. We interprete these results that Ca2+ may change the conformation of the myosin heavy chain by binding to myosin and speculate that impairment of this process upon modification could cause the desensitization to Ca2+ in the ATPase activity.
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PMID:Effect of N-ethylmaleimide on Ca-inhibition of Physarum myosin. 295 57

The distribution of fast and slow isoforms of troponin C, I, and T components and myosin heavy chains was investigated in histochemically typed myofibrillar ATPase intermediate (IM) fibres, that is, fibres that stain after both acid and alkaline preincubation in stainings for myofibrillar ATPase. In addition to the previously described IM fibres of types IIC and IB, fibres that displayed staining characteristics between types IIC and IB were observed and termed type IIC-IB. The IM fibres constitute less than 1% of the fibres in normal human limb and abdominal muscles. The IM fibres studied here resulted from extensive endurance training of human triceps brachii muscle (n = 6) and were induced by conversion of a proportion (13%) of type II fibres. The immunohistochemical stains of serial sections with antibodies to slow isoforms of troponin I, T, C and myosin heavy chain showed no staining of type II fibres but intense staining of types I and IB fibres, whereas type IIC fibres stained with intermediate intensity. The antibodies to fast isoforms of the troponin components and myosin heavy chain did not give rise to staining of type I fibres but dark staining of type II fibres. Type IB fibres stained with intermediate intensity and type IIC was either as dark as type II or slightly lighter. Type IIC-IB fibres showed staining intensities intermediate between those observed for types IB and IIC in the immunohistochemical stains. It is therefore concluded that training-induced myofibrillar ATPase intermediate human skeletal muscle fibres are characterized by the coexistence of slow and fast isoforms of contractile and regulatory proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Coexistence of slow and fast isoforms of contractile and regulatory proteins in human skeletal muscle fibres induced by endurance training. 296 Jan 27

To determine the characteristics of cardiac myosin in the conduction system, a pure Purkinje fiber preparation, consisting of atrioventricular nodes and the ventricular conduction system, was obtained from bovine hearts. Two types of myosin heavy chain isozymes, alpha-type and beta-type, were fractionated by affinity chromotography using monoclonal antibodies CMA19 and HMC50, which are specific for the alpha-type heavy chain and beta-type heavy chain, respectively. Competitive enzyme-linked immunosorbent assay demonstrated that the content of beta-type in the atrioventricular node (30-40%) was higher than that in atrial ordinary myocardium (10-20%) and that of the alpha-type was 30-40% in the ventricular conduction system, which was much higher than that in the ventricular ordinary myocardium (less than 10%). By one- and two-dimensional electrophoresis of the peptides produced by partial and complete digestion, the peptide compositions of alpha-type and beta-type in the conduction system were shown to be very similar to those of alpha-type and beta-type in ordinary myocardium, respectively. The CA2+-activated ATPase activity of myosin of the atrioventricular nodes was lower than that of ordinary atrial myosin (0.46 +/- 0.03 versus 0.58 +/- 0.02 mumol Pi/mg/min, mean +/- SEM, p less than 0.05) and in contrast, that of ventricular specialized myocardium was higher than that of myosin in the ventricular ordinary working myocardium (0.32 +/- 0.03 versus 0.22 +/- 0.01 mumol Pi/mg/min, p less than 0.05). This was in good agreement with the relative proportion of myosin isozymes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Isolation and characterization of myosin heavy chain isozymes of the bovine conduction system. 296 Apr 69

The effects of hypothyroidism on structural and functional properties of the actomyosin-ATPase complex of rat fast-twitch gastrocnemius muscle were examined and related to energetic and mechanical parameters. Hypothyroidism resulted in the appearance of a small band of the myosin heavy chain subunit of the slow form (MHCs) 8% of total MHC) which was absent in the euthyroid group. This observation corresponded with lower activities of myofibrillar ATPase (-14%) and Ca-activated myosin ATPase (-9%) in the hypothyroid group, although these changes were not significant. No effect of hypothyroidism on the Ca2+-sensitivity of the myofibrillar-ATPase activity was observed and tetanic force was not changed. Twitch force, however, was significantly increased by hypothyroidism. The degree of myosin P-light chain phosphorylation (percentage of total amount of P-light chain) determined after 5 and 10 s of tetanic stimulation (130 Hz, 35 degrees C), respectively, proved to be significantly lower in the hypothyroid group (5 s: 57%; 10 s: 61%) vs the euthyroid group (5 s: 79%; 10 s: 82%). There was no difference in P-light chain phosphorylation at rest between eu- and hypothyroids. The results suggest that a decreased actomyosin-ATPase activity can only in part contribute to the 30% lower energy turnover during force development found for fast-twitch skeletal muscle of hypothyroid rats. Moreover, the increase in twitch force by hypothyroidism cannot be explained by a change in myosin P-light chain phosphorylation. Isometric twitch tension potentiation after a 2 s tetanus and during low-frequency repetitive stimulation was reduced (up to -60%) in muscles of hypothyroid rats, which may well be related to the lower extent of P-light chain phosphorylation in hypothyroids.
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PMID:Structural and functional aspects of the actomyosin complex from fast-twitch muscle of euthyroid and hypothyroid rats. 296 Sep 52

The purpose of this study was to ascertain the time course of change during both compensatory growth (hypertrophy) and subsequent growth regression on myosin isoform expression in rodent fast-twitch plantaris muscle in response to functional overload (induced by removal of synergists). Peak hypertrophy of the plantaris muscle (92%) occurred after 9 wk of overload. After 7 wk of overload regression (induced by a model of hindlimb unweighting), muscle weight returned to within 30% of control values. Myofibril protein content (mg/g muscle) remained relatively constant throughout the overload period but became significantly depressed relative to control values after 7 wk of regression. However, when expressed on a per muscle basis (mg/muscle) no differences existed at this time point (t = 7 wk regression). The distribution of native myosin isoforms in the myofibril protein pool of the overloaded plantaris muscle reflected a progressive increase (23% at t = 9 wk; P less than 0.001) in the relative proportion of slow myosin (Sm). This change was also accompanied by increases in intermediate myosin (Im) as well as the repression of the fast myosin one (Fm1) isoform (P less than 0.001). These shifts in Sm and Fm1 isoform expression were gradually reversed during the regression period, whereas Im remained elevated relative to control values. These adaptive changes in myosin isoform expression during both hypertrophy and regression were further supported by concomitant shifts in both myosin adenosinetriphosphatase (ATPase) activity (decreased during overload) and slow myosin light chain (SLC) expression. However, during regression the changes in myosin isoform expression and myosin ATPase were not as synchronous as they were during overload. Estimation of the mixed myosin heavy chain (MHC) half-life (t 1/2), using a linear model that assumes zero-order synthesis and first-order degradation kinetics, revealed t 1/2 values of approximately 19 and 10 days for the overload and regression periods, respectively. Collectively these data suggest that 1) skeletal muscle myosin isoforms and corresponding ATPase activity are in a dynamic state of change, although not completely synchronous, in response to altered muscle stress, and 2) the kinetics of change in the mixed MHC protein pool are slower during compensatory growth compared with regression of growth.
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PMID:Time course adaptations in rat skeletal muscle isomyosins during compensatory growth and regression. 296 24

Isomyosin analyses by biochemical, immunochemical, and histochemical investigations have been carried out in five sheep following unilateral recurrent laryngeal nerve paralysis and direct functional electrostimulation of the denervated cricoarytenoid posterior muscle. Myosin light chains were identified by two-dimensional gel electrophoresis. Myosin heavy chains were analyzed by one-dimensional SDS-polyacrylamide gel electrophoresis. Slow myosin heavy chain was identified by orthogonal peptide mapping and immunochemistry. The stimulation effect at cellular level was determined using adenosine triphosphatase (ATPase) histochemistry. A dramatic increase of the type 1 fiber area (slow, fatigue-resistant fibers) could be seen after many weeks of an increasing regime of low-frequency direct electrical stimulation. Biochemically, the amount of slow myosin was always higher than in normal muscles. Some muscles were transformed almost completely to the slow type. At the time they were studied and with the methods employed, the expression of embryonic isomyosin was not observed. In conclusion, after numerous weeks of maintained functional activity, elicited by direct electrostimulation, the denervated muscle regionally showed areas of hypertrophy or at least lack of atrophy of slow myofibers without major signs of muscle damage.
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PMID:Isomyosin changes after functional electrostimulation of denervated sheep muscle. 297 27

Recently, we demonstrated that more beta-type myosin heavy chain (HC) was expressed in the overloaded atrium, and that there were 2 structurally different beta-type myosin heavy chains in the bovine heart. To determine the existence of the 2 beta-type HC in other animals and to clarify the characteristics of these beta-type HCs, we produced tricuspid regurgitation and pulmonary stenosis in the canine heart, and performed an immunological study using 3 monoclonal antibodies, 2 beta-type specific antibodies (HMC14 and 50) and 1 alpha-type specific antibody (CMA19). In an immunohistochemical study, serial cryostat sections revealed that some myofibers reacted with HMC50 (HC beta 2), but almost no fibers were labeled with HMC14 in the normal atrium. However, in overloaded atria, not only HC beta 2 but the HC, reacted with HMC14 (HC beta 1). By affinity chromatography, HC beta 2 was fractionated from normal atrial myosin using HMC50 and HC beta 1 was fractionated from overloaded atrial myosin using HMC14. These 2 HC beta's were subjected to digestion by alpha-chymotrypsin, staphylococcus aureus V8 protease, and cyanogen bromide, and proved to have different peptide fragments. In respect to enzymatic properties, the Ca2+-activated ATPase activities of HC beta 1 and beta 2 were almost the same but lower than that of HC alpha. We concluded that the isozymic transition of HC alpha to HC beta in the atrium was experimentally induced by hemodynamic overload and that HC beta 1, which was hardly recognized in the normal atrium but highly induced by overload, was structurally different from HC beta 2, as expressed in the normal atrium.
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PMID:Isolation and characterization of two beta-type cardiac myosin in the canine atrium. 297 92

Myosin is identified and purified from three different established Drosophila melanogaster cell lines (Schneider's lines 2 and 3 and Kc). Purification entails lysis in a low salt, sucrose buffer that contains ATP, chromatography on DEAE-cellulose, precipitation with actin in the absence of ATP, gel filtration in a discontinuous KI-KCl buffer system, and hydroxylapatite chromatography. Yield of pure cytoplasmic myosin is 5-10%. This protein is identified as myosin by its cross-reactivity with two monoclonal antibodies against human platelet myosin, the molecular weight of its heavy chain, its two light chains, its behavior on gel filtration, its ATP-dependent affinity for actin, its characteristic ATPase activity, its molecular morphology as demonstrated by platinum shadowing, and its ability to form bipolar filaments. The molecular weight of the cytoplasmic myosin's light chains and peptide mapping and immunochemical analysis of its heavy chains demonstrate that this myosin, purified from Drosophila cell lines, is distinct from Drosophila muscle myosin. Two-dimensional thin layer maps of complete proteolytic digests of iodinated muscle and cytoplasmic myosin heavy chains demonstrate that, while the two myosins have some tryptic and alpha-chymotryptic peptides in common, most peptides migrate with unique mobility. One-dimensional peptide maps of SDS PAGE purified myosin heavy chain confirm these structural data. Polyclonal antiserum raised and reacted against Drosophila myosin isolated from cell lines cross-reacts only weakly with Drosophila muscle myosin isolated from the thoraces of adult Drosophila. Polyclonal antiserum raised against Drosophila muscle myosin behaves in a reciprocal fashion. Taken together our data suggest that the myosin purified from Drosophila cell lines is a bona fide cytoplasmic myosin and is very likely the product of a different myosin gene than the muscle myosin heavy chain gene that has been previously identified and characterized.
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PMID:Cytoplasmic myosin from Drosophila melanogaster. 309 37


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