scholarly journals Myosin

1967 ◽  
Vol 50 (6) ◽  
pp. 85-118 ◽  
Author(s):  
Paul Dreizen ◽  
Lewis C. Gershman ◽  
Paul P. Trotta ◽  
Alfred Stracher
Keyword(s):  
Molecular Weight ◽  
Binding Capacity ◽  
Biological Significance ◽  
Enzymic Activity ◽  
Actin Binding ◽  
Average Weight ◽  
Myosin Molecule ◽  
Head Region ◽  
Present Evidence ◽  
Globular Head

There is fairly general agreement that myosin isolated from rabbit skeletal muscle has a molecular weight of about 500,000. The higher values that have been reported apparently reflect protein aggregation related to the method of preparation. On the basis of present evidence, the myosin molecule has an elongate helical core of two f subunits (average weight about 215,000) that extend into a globular head region containing three g subunits (average weight about 20,000). Myosin may be dissociated into subunits by a number of methods. In 5 M guanidine, the myosin molecule is dissociated into f and g subunits, while at pH above 10, the g subunits are dissociated from the intact fibrous core of myosin. The dissociation of g subunits at pH 10 is accompanied by the loss of both ATPase activity and actin-binding capacity; however, the exact biological significance of the g subunits is presently uncertain. In preliminary studies, the f subunits appear to contain the sulfhydryl residues currently implicated in myosin ATPase, and there is some indication of allosteric regulation of enzymic activity.

Structure of Myosin Subfragment-1 from Electron Microscopy and Crystallography

1988 ◽  
Vol 46 ◽  
pp. 156-157
Author(s):  
Donald A. Winkelmann
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Actin Filaments ◽  
Light Chains ◽  
Myosin Filament ◽  
Primary Role ◽  
Heavy Chains ◽  
Myosin Subfragment ◽  
Myosin Subfragment 1 ◽  
Globular Head

The primary role of the interaction of actin and myosin is the generation of force and motion as a direct consequence of the cyclic interaction of myosin crossbridges with actin filaments. Myosin is composed of six polypeptides: two heavy chains of molecular weight 220,000 daltons and two pairs of light chains of molecular weight 17,000-23,000. The C-terminal portions of the myosin heavy chains associate to form an α-helical coiled-coil rod which is responsible for myosin filament formation. The N-terminal portion of each heavy chain associates with two different light chains to form a globular head that binds actin and hydrolyses ATP. Myosin can be fragmented by limited proteolysis into several structural and functional domains. It has recently been demonstrated using an in vitro movement assay that the globular head domain, subfragment-1, is sufficient to cause sliding movement of actin filaments.The discovery of conditions for crystallization of the myosin subfragment-1 (S1) has led to a systematic analysis of S1 structure by x-ray crystallography and electron microscopy. Image analysis of electron micrographs of thin sections of small S1 crystals has been used to determine the structure of S1 in the crystal lattice.

scholarly journals A new case of deficiency of the R binder for cobalamin, with observations on minor cobalamin-binding proteins in serum and saliva

Blood ◽  
1982 ◽  
Vol 59 (1) ◽  
pp. 152-156
Author(s):  
R Carmel
Keyword(s):  
Molecular Weight ◽  
Alcohol Abuse ◽  
Incidental Findings ◽  
Clinical Presentation ◽  
Binding Capacity ◽  
Normal Serum ◽  
Serum Component ◽  
Almost All ◽  
Normal Controls ◽  
Low Serum

A patient presented at the age of 77 yr with a low serum cobalamin level. Subsequent study showed that he had persistently very low R binder (TC I) cobalamin-binding capacity in serum (less than 5 ng/liter versus 213 +/- 171 ng/liter in normal controls), and that almost all of his endogenous serum cobalamin was carried by TC II instead of TC I. His saliva also demonstrated virtually undetectable R binder (binding capacity of 31–38 ng/liter versus 41,690 +/- 23,820 ng/liter for control subjects). Unlike previous cases of R binder deficiency, he seemed to maintain normal serum cobalamin levels while receiving monthly cyanocobalamin injections. This and his normal serum unsaturated binding capacity were due to elevated TC II levels. TC II carried 72%-98% of his endogenous cobalamin, the rest being attached to minor binders. As incidental findings, the patient had a serum component of molecular weight of approximately 70,000 that carried 7%- 8% of his endogenous cobalamin and also had small quantities of TC II demonstrable in his saliva. Both these heretofore unappreciated minor peaks were identifiable because of the lack of R binder. The patient's clinical presentation supports the conclusion that R binder deficiency is a benign disorder. Whether his mild hypersegmentation of neutrophils and neuropathy were related to the R binder deficiency or, more likely, arose from coexisting folate deficiency and alcohol abuse, the overall picture contrasts dramatically with the severe clinical sequelae of TC II deficiency.

State of iron(III) in normal human serum: low molecular weight and protein ligands besides transferrin

1970 ◽  
Vol 48 (12) ◽  
pp. 1339-1350 ◽  
Author(s):  
Bibudhendra Sarkar
Keyword(s):  
Molecular Weight ◽  
Human Serum ◽  
Binding Capacity ◽  
Normal Serum ◽  
Normal Human Serum ◽  
Void Volume ◽  
Antibody Concentration ◽  
Low Molecular Weight ◽  
Protein Ligands ◽  
Normal Human

A fraction of Fe(III) in normal human serum is bound to both low molecular weight as well as protein ligands besides transferrin. Citrate was shown to be the major Fe(III)-binding substance in the low molecular weight fraction. Amino acids, sugars, and organic acids, such as ascorbate, pyruvate, and lactate, showed very little or no binding to Fe(III) in normal serum. Iron(III)-binding proteins other than transferrin were shown to be present in normal serum when the native serum with [59Fe(III)] was fractionated by (NH4)2SO4 and Sephadex G-150. The presence of these proteins was observed when trace amounts of Fe(III) were added to the normal serum and when the iron-binding capacity was saturated with Fe(III) to 50% and 100%. These proteins were eluted in the void volume of Sephadex G-150 and none of them corresponded electrophoretically to transferrin. The results of the gel filtration of a mixture of [131I]-transferrin and the proteins eluted in the void volume of Sephadex G-150 were strongly in favor of the Fe(III)-proteins as being neither transferrin aggregates nor transferrin adducts with other proteins. Immunoelectrophoresis of the Sephadex G-150 void volume proteins on agar gel against the antibody to transferrin revealed the absence of transferrin. The presence of at least six proteins in this fraction was shown by immunoelectrophoresis. Positive precipitin reactions were obtained with the antibodies to α2-macroglobulin, γG-globulin, γA-globulin, and γM-globulin. At least two more proteins in this fraction remained unidentified. When the same fraction containing [59Fe(III)] was treated with the whole antisera and the precipitates were counted for radioactivity, a typical antigen-antibody reaction curve was obtained as the antibody concentration was increased. Similar experiments with this fraction and antibodies to α2-macroglobulin, γG-globulin, γA-globulin, and γM-globulin failed to show any significant radioactivity in the precipitate. Since this fraction did not contain any transferrin, it was concluded that there are proteins besides transferrin which can act as ligands for Fe(III) in normal blood plasma.

STUDIES ON SMALL MOLECULAR WEIGHT ADHESION PROTEINS (SAPs) FROM CONNECTIVE TISSUES

1987 ◽  
Author(s):  
S Wasi ◽  
P Alles ◽  
D Gauthier ◽  
U Bhargava ◽  
J Farsi ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Polyclonal Antibody ◽  
Type I Collagen ◽  
Cell Attachment ◽  
Binding Capacity ◽  
Guanidine Hydrochloride ◽  
Cell Types ◽  
Type I ◽  
Cell Binding ◽  
Connective Tissues

We have identified a family of low molecular weight proteins with cell attachment properties in a variety of soft and mineralised connective tissues (Wong et al., Biochem. J. 232, 119, 1985). For further characterisation of these proteins we extracted porcine bones with 4 M guanidine hydrochloride and purified the proteins on a series of gel filtration columns The purifed SAPs comprise three bands with Mr -14 000 -17 000. All three proteins bound to heparin-sepahrose in both the presence and absence of 4M urea, and when eluted with 2 M NaCl they retained their cell binding capacity. These proteins promoted the adhesion and spreading of a variety of cell types, including normal fibroblasts, osteoblasts, and epithelial cells, and tumour (osteosarcoma) cells. On Western blotting SAPs did not cross-react with antibodies against fibronectin, laminin or type I collagen; however, they were recognised by a monoclonal antibody to human vitronectin, a polyclonal antibody to bovine vitronectin and polyclonal antibody to human somatomedin B. Dose response experiments indicated that maximum attachment of human gingival fibroblasts occurred in the presence or absence of fetal bovine serum on wells precoated with 2.5 μg/cm2 of SAPs. Attachment of cells to these proteins was partially inhibited by the synthetic pentapeptide Gly-Arg-Gly-Asp-Ser. Utilising the nitrocellulose cell binding assay of Hayman et al (J. Cell. Biol. 95, 20, 1982), the cell attachment to these proteins could be completely inhibited by heparin (100 units/mL) whereas up to 1000 units/mL of heparin had no inhibitory effect on cell attachment to fibronectin and vitronectin. The occurrence of these proteins in a variety of connective tissues and their recognition by different cell types may reflect their general biological role in adhesive mechanisms in both hard and soft connective tissues. Currently, we are investigating the relationship between SAPs and vitronectin, since it is possible that SAPs represent a tissue-processed form of vitronectin or may be novel attachment proteins with regions of homology with vitronectin

scholarly journals Ca2+-Induced Cleavage of Human Platelet Polypeptides Mediated by the Calcium Ionophore A-23187

1977 ◽  
Author(s):  
Milica Jakábová ◽  
David R. Phillips
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proteolytic Activity ◽  
Platelet Activation ◽  
Human Platelet ◽  
Calcium Ionophore ◽  
Lactic Dehydrogenase ◽  
Actin Binding ◽  
A 23187 ◽  
Hydrolysis Of

The effect of calcium on human platelet polypeptides was investigated. When lysed platelets were incubated with mM Ca++, two major intracellular polypeptides (Mr = 255,000 and 230,000) were found to rapidly disappear. A similar phenomenon was also observed when intact platelets were treated with the calcium ionophore A-23187 in the presence of mM Ca++. Determinations of lactic dehydrogenase activity in supernatant fractions demonstrated that these losses occurred before platelet lysis. Investigations into the identity of the high molecular weight polypeptides revealed that one (Mr = 255,000) had similar properties to actin binding protein. The loss of the high molecular weight polypeptides was accompanied by formation of lower molecular weight polypeptides (Mr = 135,000, 93,000 and 48,000), indicating that Ca++ activates a polypeptide cleavage mechanism. The Ca++-activated polypeptide cleavages were rapid, with significant changes being observed within the first 0.5 min of incubation. An obvious explanation for these effects is. that there is Ca++-activated proteolytic activity within platelets. The Ca++-activated proteolytic activity was determined by the hydrolysis of the artificial substrate azocasein. We found that more than 90% of the proteolytic activity in lysed platelets was due to Ca++-activated proteases. These studies show that Ca++-activated proteases may play an important role in platelet activation.

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