Proteins of the Uterine Contractile Mechanism

Needham, Dorothy M.; Williams, John M.

doi:10.1042/bj0890552

Cited by 49 publications

(16 citation statements)

References 34 publications

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“…The actomyosin content of smooth muscle is estimated to be 6 mg/g wet weight of cow uterus (21,22) whereas that of the dog heart is given as 54-57 nag (23); i.e., the actomyosin content of the cow uterus is one-nineth to one-tenth that of the dog heart. When allowance is made for 25 % actin and tropomyosin, one computes a myosin content of 4.5 mg/g wet weight of uterus or 0.9 X 10 -5 mmole on the basis of a molecular weight of approximately 500,000 for myosin.…”

Section: Discussionmentioning

confidence: 99%

Role of Calcium Binding by Sarcoplasmic Reticulum in the Contraction and Relaxation of Uterine Smooth Muscle

Carsten

1969

The Journal of General Physiology

136

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The binding of calcium by isolated sarcoplasmic reticulum from cow uterus was studied. Sarcoplasmic reficulum was prepared by differential centrifugation. Three fractions were obtained: I, sedimented between 2,500-15,000 X g; II at 40,000 X g; and III, at 150,000 X g. Fraction II was further purified on a sucrose density gradient. All three fractions contained considerable amounts of intrinsic calcium, mostly in fraction I. Calcium binding in the presence of ATP 1 and Mg also was greatest in fraction I, followed by fraction II, with less in fraction III. Without ATP no calcium was taken up. 5 and 10 mM sodium azide partially inhibited calcium binding in fraction I, but not in fraction II, suggesting the presence of some mitochondria or mitochondrial fragments in fraction I. Calcium binding in fraction II was completely inhibited by 3 mM salyrgan; this fraction thus appears to be sarcoplasmic reticulum. ATPase activity was found in all three fractions, highest in fraction II. It is computed that calcium binding in fractions I and II, on the basis of a 50 % yield of protein, is sufficient to elicit contraction by supplying calcium to the contractile proteins of the smooth muscle cell and to regulate relaxation and contraction.

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Section: Discussionmentioning

confidence: 99%

Role of Calcium Binding by Sarcoplasmic Reticulum in the Contraction and Relaxation of Uterine Smooth Muscle

Carsten

1969

The Journal of General Physiology

136

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“…It is therefore unlikely that the amount of myosin could ever be judged from electron micrographs . The amount which could be accommodated by the arrangement we propose (1) seems sufficient, however, to account for the myosin found by chemical analysis (18) .…”

Section: Methodsmentioning

confidence: 64%

“…It appears to contain two globular subunits . The tail is [15][16][17][18][19][20] A wide and can be followed about 600 A . X 250 000 FIGURES 2 a and 2 b Longitudinal sections of smooth muscle from gizzard soaked for 1 1/2 hr in bufferred salt solution pH 6 .2 with added 1 mm EGTA, fixed in glutaraldehyde, pH 6 .2, postfixed in OsO4, and section stained with lead .…”

Section: Effect Of Preparative Conditions Onmentioning

confidence: 99%

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Locus and State of Aggregation of Myosin in Tissue Sections of Vertebrate Smooth Muscle

Panner

Honig

1970

The Journal of Cell Biology

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Structures with the characteristics of molecular myosin were identified by electron micros--copy in tissue sections of vertebrate smooth muscle . No thick filaments of myosin were found regardless of preparative procedures, which included fixation at rest and in contraction, glycerine extraction, and storage at low pH prior to fixation. Absence of thick myosin filaments and presence of what appear to be myosin molecules is in accord with conclusions based on X-ray diffraction (3, 12) and birefringence data (4) from living smooth muscles at rest and in contraction . Explanations are provided for appearances thought by others (6,20,21) to represent thick myosin filaments . Our present observations are in accord with the model for smooth muscle contraction which we have previously proposed (1) .

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“…Reflections characteristic of myosin filaments have not been identified in X-ray diffraction diagrams of vertebrate smooth muscle (Elliott, 1964(Elliott, , 1966, and structures comparable to the A band have not been observed in electron micrographs of sectioned material (Caesar, Edwards, and Ruska, 1957;Choi, 1962;Needham and Shoenberg, 1964). Although its location is unknown, myosin can be isolated from smooth muscle by chemical means (Needham and Williams, 1963), and the individual molecules of myosin so obtained have the same structure as those from striated muscles FIGURE 1 Conventional longitudinal section of nonglycerinated, OsO 4 -fixed smooth muscle embedded in Epon and stained with lead citrate. Individual myofilaments show variability of diameter and electron opacity.…”

Section: Introductionmentioning

confidence: 99%

Filament Ultrastructure and Organization in Vertebrate Smooth Muscle

Panner

Honig

1967

The Journal of Cell Biology

103

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Using a variety of preparative techniques for electron microscopy, we have obtained evidence for the disposition of actin and myosin in vertebrate smooth muscle. All longitudinal myofilaments seen in sections appear to be actin. Previous reports of two types of longitudinal filaments in sections are accounted for by technical factors, and by differentiated areas of opacity along individual filaments. Dense bodies with actin emerging from both ends have been identified in homogenates, and resemble Z discs from skeletal muscle (Huxley, 1963). In sections, short, dark-staining lateral filaments 15 25 A in diameter link adjacent actin filaments within dense bodies and in membrane dense pataches. They appear homologous with Z-disc filaments. Similar lateral filaments connect actin to plasma membrane. Dense bodies and dense patches, therefore, are attachment points and denote units analogous to sarcomeres. In glycerinated, methacrylate-embedded sections, lateral processes different in length and staining characteristics from lateral filaments in dense bodies exist at intervals along actin filaments. These processes are about 30 A wide and resemble heavy meromyosin from skeletal muscle. They also resemble heads of whole molecules of myosin in negatively stained material from gizzard homogenates. Intact single myosin molecules and dimers have been found, both free and attached to actin, even in media of very low ionic strength. Myosin can, therefore, exist in relatively disaggregated form. Models of the contraction mechanism of smooth muscle are proposed. The unique features are: (1) Myosin exists as small functional units. (2) Movement occurs by interdigitation and sliding of actin filaments.

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Proteins of the Uterine Contractile Mechanism

Cited by 49 publications

References 34 publications

Role of Calcium Binding by Sarcoplasmic Reticulum in the Contraction and Relaxation of Uterine Smooth Muscle

Role of Calcium Binding by Sarcoplasmic Reticulum in the Contraction and Relaxation of Uterine Smooth Muscle

Locus and State of Aggregation of Myosin in Tissue Sections of Vertebrate Smooth Muscle

Filament Ultrastructure and Organization in Vertebrate Smooth Muscle

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