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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Actin and spectrin were isolated from washed red blood cell membranes. Spectrin bound and polymerized erythrocyte actin in the absence of potassium. Spectrin coated into polystyrene latex particles bound 8--9 mol of erythrocyte actin per mol of spectrin when actin was in its depolymerized state. Spectrin enhanced the interaction of erythrocyte actin with muscle myosin as manifested by changes in Mg2+-ATPase activity. A similar enhancement also was observed with muscle alpha-actinin while muscle tropomyosin abolished these effects. The data suggest that spectrin may play the role of polymerizing factor as well as the anchoring site for erythrocyte actin just as alpha-actinin is the anchoring site for actin filaments in muscle and other non-muscle cells.
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PMID:Erythrocyte actin and spectrin. Interactions with muscle contractile and regulatory proteins. 15 47

The degradation of rat cardiac myofibrils and their constituent proteins with a myosin-cleaving protease was studied. Electrophoretograms of the digestion products of myofibrils showed that myosin,M-protein, C-protein, and troponin were degraded, but actin and tropomyosin were not. Degradation of these constituents resulted in losses of the Mg2+-ATPase activity and its Ca2+-sensitivity of myofibrils. Incubation of myofibrils with the protease induced the release of alpha-actinin without degradation. Susceptibilities of myosin, actin, troponin, and alpha-actinin purified from rat and pig hearts to the protease were essentially identical to those of the assembled forms in myofibrils. Although the purified tropomyosin was readily degraded into five fragments with the protease, the tropomyosin assembled in myofibrils and actin-tropomyosin complex were insusceptible to the protease. Digestion of myosin in the filamentous state with the protease resulted in the disappearance of myosin heavy chain and light chain 2, producing two fragments having molecular weights of 130,000 and 94,000 which originated from the degradation of heavy chain. The Ca2+- and EDTA-ATPase activities of the degradation products remained unchanged during incubation for 22 h. The actin-activated ATPase activity of myosin was reduced by 30% during incubation for 6 h, and recovered to the original level on adding actin to give a ratio of actin to myosin of 2:1. The pH optima for degradation of myosin in the soluble and filamentous states were 8.5 and 7.0, respectively. The results indicate that cardiac myosin in the filamentous state was more readily degraded with the protease than the myosin in the soluble state.
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PMID:Degradation of rat cardiac myofibrils and myofibrillar proteins by a myosin-cleaving protease. 47 42

alpha-Actinin exists in several polymorphic forms which appear to be characteristic of the muscle type from which it is isolated. In order to determine the possible physiological role of this structural protein in cardiac muscle, we describe and compare here the physico-chemical properties of cardiac alpha-actinin from two different mammalian species, rat (fast contracting muscle) and dog (slow contracting muscle). Purification of cardiac alpha-actinin was achieved by chromatography on DEAE-cellulose and hydroxyapatite columns. The alpha-actinins isolated were different in their electrophoretic mobility (SDS-polyacrylamide gel electrophoresis), molecular size and alpha-helical content. However, their shape as revealed by electron microscopy and their activating effect on Mg2+-ATPase activity of actomyosin appear to be similar. These studies suggest that the rat and dog cardiac alpha-actinin are structurally different but functionally similar proteins.
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PMID:Physico-chemical properties of rat and dog cardiac alpha-actinin. 294 32

We have developed a new method for the rapid isolation of tropomyosin-containing microfilaments from cultured cells using anti-tropomyosin monoclonal antibodies. Anti-tropomyosin monoclonal antibodies induce the bundle formation of microfilaments, which can be easily collected by low speed centrifugation. Electron microscopic studies of the isolated microfilaments show periodic localization of tropomyosin along the microfilaments of nonmuscle cells with a 33-34 nm repeat. Furthermore, the isolated microfilaments have the ability to activate the Mg2+-ATPase activity of skeletal muscle myosin to almost the same extent as skeletal muscle F-actin (filamentous actin). This microfilament isolation method is applicable to a variety of cell types, including REF-52 cells (an established rat embryo line), L6 myoblasts, 3T3 fibroblasts, Chinese hamster ovary cells, baby hamster kidney (BHK-21) cells, mouse neuroblastoma cells, gerbil fibroma cells, and chicken embryo fibroblasts. Sodium dodecyl sulfate-polyacrylamide gel analysis shows that, in addition to actin, microfilaments isolated from REF-52 cells contain five species of tropomyosin with apparent Mr = 40,000, 36,500, 35,000, 32,400, and 32,000, alpha-actinin, and as yet unknown proteins with apparent Mr = 83,000 and 37,000. The molar ratio of total tropomyosin (dimer) to actin in the isolated microfilaments is 1:8. The patterns of these multiple forms of tropomyosin were found to change when REF-52 cells were transformed with SV40 or adenovirus type 5.
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PMID:Isolation and characterization of tropomyosin-containing microfilaments from cultured cells. 613 66

alpha-Actinin purified from chicken gizzard smooth muscle was characterized in comparison with alpha-actinins from chicken striated muscles, or fast-skeletal muscle, slow-skeletal muscle, and cardiac muscle. The gizzard alpha-actinin molecule consisted of two apparently identical subunits with a molecular weight of 100,000 on SDS-polyacrylamide gel electrophoresis, as do striated-muscle alpha-actinins. Its isoelectric points in the presence of urea were similar to the striated-muscle counterparts. Despite these similarities, distinctive amino acid sequences between smooth-muscle alpha-actinin and striated-muscle alpha-actinins were revealed by peptide mapping using limited proteolysis in SDS. Gizzard alpha-actinin was immunologically distinguished from striated-muscle alpha-actinins. Gizzard alpha-actinin formed bundles of gizzard F-actin as well as of skeletal-muscle F-actin, but could not form any cross-bridges between adjacent actin filaments under conditions where skeletal-muscle alpha-actinin could. Temperature-dependent competition between gizzard alpha-actinin and tropomyosin on binding to gizzard thin filaments was demonstrated by electron microscopic observations. Gizzard alpha-actinin promoted Mg2+-ATPase activity of reconstituted skeletal actomyosin, gizzard acto-skeletal myosin, and gizzard actomyosin. This promoting effect was depressed by the addition of gizzard tropomyosin. These findings imply that, despite structural differences between gizzard and striated-muscle alpha-actinin molecules, they function similarly in vitro, and that gizzard alpha-actinin can interact not only with smooth-muscle actin (gamma- and beta-actin) but also with skeletal-muscle actin (alpha-actin).
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PMID:Molecular properties and functions in vitro of chicken smooth-muscle alpha-actinin in comparison with those of striated-muscle alpha-actinins. 621 60

Antitropomyosin and anti-alpha-actinin monoclonal antibodies have been used to isolate two classes of microfilaments, i.e., tropomyosin-enriched and alpha-actinin-enriched microfilaments, respectively, from cultured chicken embryo fibroblasts. Electron microscopic studies of the isolated tropomyosin-enriched microfilaments showed periodic localization of tropomyosin along the microfilaments, with a 35-nm repeat. On the contrary, the isolated alpha-actinin-enriched microfilaments showed no obvious periodicity. Many individual alpha-actinin-enriched microfilaments with length greater than 1 micron (ranging from 1 to 10 microns) were aggregated by anti-alpha-actinin monoclonal antibodies. Both of the isolated microfilaments had the ability to activate the Mg2+-ATPase activity of skeletal muscle myosin, although different extents of activation were observed. These two classes of microfilaments also differed in their protein composition. Molar ratios of major identifiable proteins in the isolated microfilaments were alpha-actinin(dimer):actin(monomer):tropomyosin(dimer) = less than 0.02:8.06:1.00 for tropomyosin-enriched microfilaments and 0.44:13.91:1.00 for alpha-actinin-enriched microfilaments. By two-dimensional gel analysis of the isolated microfilaments, we have found seven spots which possess typical tropomyosin properties including pI 4.5, immunological cross-reaction, lack of proline and tryptophan, and heat stability. Pulse-chase experiments suggested that the assembly of microfilament-associated proteins, at least for alpha-actinin and tropomyosins, was coordinately regulated by the assembly of actin into microfilaments.
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PMID:Tropomyosin-enriched and alpha-actinin-enriched microfilaments isolated from chicken embryo fibroblasts by monoclonal antibodies. 653 70