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The myofibrillar proteins and relative LC-3 content of myofibrils prepared from five different, left and right muscles of the human forearm were studied by electrophoresis in 10% SDS-polyacrylamide gels followed by densitometry. The specific K-activated ATPase activity of the myofibrillar myosin of the myofibrils was determined and the distribution of the fibre types was analyzed by histochemical methods. The qualitative pattern of the myofibrillar proteins was found to be identical in the different muscles; in the other parameters, however, a variation in a narrow range was observed. The relative LC-3 content, the ATPase activity and the type II fibre content of the right side muscles were always higher than those of the corresponding left side muscles.
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PMID:Myofibrillar proteins, enzyme activity and fibre types in human skeletal muscle. 23 9

Actomyosin was extracted from smooth muscle of molluscan abalone with 0.1 M PPit pH 6.4. Myosin was separated from the actomyosin by centrifugation at 100,000 X g in the presence of 5 mM ATP and 10 mM MgCl2. Myosin in the supernatant was further purified by gel filtration on a Sepharose 4B column. Paramyosin contamination of the actomyosin preparation interfered with the isolation of myosin and complete removal of actin and paramyosin from the myosin has not been accomplished. The myosin appeared to consist of a single f-chain and a single g-chain, as examined by SDS-disc electrophoresis in 8 or 13.7% acrylamide gel. The ATPase [EC 3.6.1.3] activity of this myosin in 0.5 M KCL at neutral pH and at 0 degrees was rather unstable and decreased by 10-20% per day. The effects of rho-chloromercuribenzoate and EDTA on the ATPase activity were similar to those observed with other smooth muscle myosin but the dependence upon pH or KCL concentration was different.
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PMID:Myosin from molluscan abalone, Haliotis discus. Isolation and enzymatic properties. 23 37

Natural actomyosin was isolated from skeletal muscle of frogs (Rana catesbeiana) acclimated at 25 degrees C and 5 degrees C. It was found that preparations isolated from warm-acclimated frogs may display considerable degradation of myosin heavy chains as compared with preparations isolated from cold-acclimated frogs. However, degradation may be minimized by inclusion of protease inhibitors during purification, indicating enhanced protease activity in preparations of natural actomyosin from warm-acclimated frogs. When purified in the presence of protease inhibitors, natural actomyosin from both warm-acclimated and cold-acclimated frogs exhibits comparable subunit composition of SDS-gel electrophoresis. The overall gel pattern is similar to that obtained from rabbit natural actomyosin except that in the frog, troponin-T and troponin-C appear to co-migrate with tropomyosin and myosin light chain 2, respectively.
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PMID:Structural studies of natural actomyosin from thermally acclimated frogs. 31 57

1. When ATP is added to Limulus myosin B and the mixture is centrifuged at 50,000 rev/min for 3 hr to dissociate it into a supernatant of myosin and a pellet of actin, the results are contrary to expectation. The pellet does contain actin but no more than one obtains if the ATP is omitted. The supernatant also contains actin. 2. If this is done in the Model E centrifuge, the major peak disappears upon ATP addition and a new peak, sedimenting at a rate typical of myosin, appears. When only this slow moving peak is run on SDS gels, actin is clearly seen. 3. It is concluded that ATP does not dissociate this actomyosin but rather causes a conformational change.
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PMID:The action of ATP on natural actomyosin. 31 24

1. Myosins from an adult individual and embryos of Salmo trutta L. in different stages of development were isolated. Their light chain composition was investigated by polyacrylamide gel electrophoresis using two systems: tris-glycine buffer, pH 8.6, containing 8 M urea and 100 mM sodium phosphate buffer, pH 7.0, containing 0.1% SDS. 2. Both types of myosin are composed of three light chains with mol. wt 26200 D, 18300 D, 16800 D. 3. Almost no changes in electrophoretic patterns were discovered between the separate stages of development, except for the intensity of the light chain lc3, which increased gradually during miogenesis.
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PMID:The light chain composition of embryonic myosin. 31 5

A new protein component was found in heavy meromyosin and in subfragment-1 (S-1) prepared by chymotrypsin digestion of pig cardiac myosin in the presence of Ca2+. The molecular weight of this protein was estimated as 15,000 dalton. It was able to bind Ca2+ and showed a similar UV absorption spectrum to that of the g2 light chain. Heavy meromyosin and subfragment-1 which contained the 15,000 dalton component incorporated exogenous g2 and the 15,000 dalton component disappeared after such treatment. We concluded that the 15,000 dalton component was produced from g2 by limitted proteolysis. The subfragment-1 was separated into two protein fractions in equal yield by recycling the gel filtration. One contained the 15,000 dalton component and was able to bind Ca2+ while the other did not contain the component and was unable to bind Ca2+. According to analysis by SDS gel electrophoresis, the large polypeptide chain (the f component) of the first S-1 was approximately 5,000 dalton larger than the f component of the second S-1. The polypeptide corresponding to 5,000 dalton was designated polypeptide-C, because it was released from the C terminal of the f component. It seems to be essential for the attachment of the Ca2+-binding light chain g2. The location of g2 in myosin may thus be at the polypeptide-C which links the head to the tail of myosin.
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PMID:Incorporation of the Ca2+ -binding component (g2) into heavy meromyosin and subfragment-1 of pig cardiac myosin. 38 56

To study the fate of external membrane proteins during phagocytosis, rabbit peritoneal neutrophils were labeled by enzymatic iodination. Iodine was incorporated into at least 13 proteins ranging in size from approximately 250,000 to 18,000 daltons as judged from autoradiography of gels after SDS-polyacrylamide gel electrophoresis of labeled cells. The major contractile proteins of neutrophils, actin and myosin, were not labeled when intact cells were iodinated but were labeled when homogenates of these cells were iodinated. Nine of the iodinated proteins were released by mild protease treatment of intact cells. A plasma membrane-rich fraction was isolated by density centrifugation. This fraction was enriched at least 10-fold for lactoperoxidase-labeled acid-insoluble proteins. It was enriched to the same extent for the presence of iodinated wheat germ agglutinin that had been bound to intact cells at 4 degrees C before homogenization. Analysis of SDS-polyacrylamide gel electrophoresis revealed that the proteins of this fraction were predominantly of high molecular weight. However, only 8 of the 13 proteins iodinated on intact cells were found in this fraction. The remaining five were enriched in a dense fraction containing nuclei, intact cells, and membranous vesicles, and may represent a specialized segment of the neutrophil cell surface.
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PMID:Fate of surface proteins of rabbit polymorphonuclear leukocytes during phagocytosis. I. Identification of surface proteins. 47 1

Ca(2+)-activated neutral proteinase was purified from rabbit skeletal muscle by a method involving DEAE-Sephacel chromatography, affinity chromatography on organomercurial-Sepharose and gel filtration on Sephacryl S-200 and Sephadex G-150. The SDS (sodium dodecyl sulphate)/polyacrylamide-gel-electrophoresis data show that the purified enzyme contains only one polypeptide chain of mol.wt. 73000. The purification procedure used allowed us to eliminate a contaminant containing two components of mol.wt. about 30000 each. Whole casein or alpha(1)-casein were hydrolysed with a maximum rate at 30 degrees C, pH7.5, and with 5mm-CaCl(2), but myofibrils were found to be a very susceptible substrate for this proteinase. This activity is associated with the destruction of the Z-discs, which is caused by the solubilization of the Z-line proteins. The activity of the proteinase in vitro is not limited to the removal of Z-line. SDS/polyacrylamide-gel electrophoresis on larger plates showed the ability of the proteinase to degrade myofibrils more extensively than previously supposed. This proteolysis resulted in the production of a 30000-dalton component as well as in various other higher- and lower-molecular-weight peptide fragments. Troponin T, troponin I, alpha-tropomyosin, some high-molecular-weight proteins (M protein, heavy chain of myosin) and three unidentified proteins are degraded. Thus the number of proteinase-sensitive regions in the myofibrils is greater than as previously reported by Dayton, Goll, Zeece, Robson & Reville [(1976) Biochemistry15, 2150-2158]. The Ca(2+)-activated neutral proteinase is not a chymotrypsin- or trypsin-like enzyme, but it reacted with all the classic thiol-proteinase inhibitors for cathepsin B, papain, bromelain and ficin. Thus the proteinase was proved to have an essential thiol group. Antipain and leupeptin are also inhibitors of the Ca(2+)-activated neutral proteinase.
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PMID:Purification and some physico-chemical and enzymic properties of a calcium ion-activated neutral proteinase from rabbit skeletal muscle. 53 1

It has been found that a high-speed supernatant fraction from Xenopus oocytes extracted in the cold will form a clear, solid gel upon warming. Gel formation occurs within 60 min at 18 degrees-40 degrees C, and is, at least initially, temperature reversible. Gelation is strictly dependent upon the addition of sucrose to the extraction medium. When isolated in the presence of ATP, the gel consists principally of a 43,000-dalton protein which co-migrates with Xenopus skeletal muscle actin on SDS-polyacrylamide gels, and a prominent high molecular weight component of approx. 250,000 daltons. At least two minor components of intermediate molecular weight are also found associated with the gel in variable quantities. Actin has been identified as the major consituent of the gel by ultrastructural and immunological techniques, and comprises roughly 47% of protein in the complex. With time, the gel spontaneously contracts to form a small dense aggregate. Contraction requires ATP. In the absence of exogenous ATP, a polypeptide which co-migrates with the heavy chain of Xenopus skeletal muscle myosin becomes a prominent component of the gel. This polypeptide is virtually absent from gels which have contracted in ATP-containing extracts. It has also been found that Ca++ is required for gelation in oocyte extracts. At both low and high concentrations of Ca++ (defined as a ratio of Ca++/EGTA in the extraction medium), gelation is inhibited.
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PMID:Actin in Xenopus oocytes. 56 81

The 3-dimensional structure of the fibrous cytoskeleton of 3T3 cells was examined by scanning electron microscopy of cells extracted with the non-ionic detergent Triton X-100. Detergent-extracted cells consist of the nucleus and an extensive system of fibres, the largest of which correspond to stress fibres visible by phase-contrast microscopy. The system of fibres, which is coterminous with the borders of the native cell, remains firmly adherent to the substratum. The major fibres branch into smaller fibrils which appear to end by ravelling out into fine filaments that constitute a matted network in a plane very close to that of the substratum. In the nuclear region all the major fibres pass over the top of the nucleus, where they may also branch into a system of fine fibrils. Thin-section transmission electron microscopy in conjunction with heavy meromyosin treatment of extracted cells shows the fibres to be composed of native F-actin. Intermediate filaments are also present, and are prominent in the matted network, together with actin filaments. The major proteins of the residue are identified by SDS-polyacrylamide gel electrophoresis as actin, a 56000 Dalton peptide, and histones. Also present are myosin heavy chain, peptides of 225,000 and 250,000, and minor bands at 60,000 and 94,000 Daltons. The non-ionic detergent extracts 70% of the cellular protein, including 50% of the actin and 75% of the myosin. The Triton-insoluble fraction of 3T3 cells appears to constitute, in addition to the nucleus, a stable cytoskeletal system, composed largely of contractile proteins and 10-nm filaments, which functions in maintenance of cell shape, in substratum adhesion, and in positioning the nucleus within the cell.
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PMID:Intracellular fibres in cultured cells: analysis by scanning and transmission electron microscopy and by SDS-polyacrylamide gel electrophoresis. 56 65


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