Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: KEGG:D03291 (CaCl2)
6,342 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously reported setting up an in vitro system for the observation of actin filament sliding along myosin filaments. The system involved a minute amount of fluorescently labelled F-actin, and its movement was monitored by fluorescence microscopy. Here, we report observations of the Ca2+-dependent movement of F-actin complex with tropomyosin plus troponin (regulated actin) added to the movement system in place of pure F-actin. In a wide range of pCa (-log10[Ca2+]) between 3 and 5.5 at 30 degrees C, regulated actin filaments moved rapidly, and the average velocity depended little on the Ca2+ concentration (about 7.5 microns/s). However, when the Ca2+ concentration was decreased to pCa = 5.8 or lower, the filaments suddenly stopped moving. In striking contrast to these observations, unregulated actin moved rapidly within the whole pCa range examined, the average velocity (about 7.5 microns/s) being essentially Ca2+-independent. These observations indicate that (1) tropomyosin-troponin actually gave Ca2+-sensitivity to F-actin, and (2) the movement system was regulated by Ca2+ in an on-off fashion within a narrow range of Ca2+ concentration. In a pCa range between 5.8 and 6.0, regulated actin filaments did not exhibit thermal motion; instead, they had fixed positions in the specimen, possibly because they remained associated with myosin filaments in the background, without sliding past each other. Although regulated actin moved fast in the presence of 1 mM-CaCl2 (pCa = 3) at 30 degrees C, it became entirely non-motile as the temperature was decreased to 25 degrees C or lower. Such a sharp movement/temperature relation was never found for unregulated actin. We assayed regulated actin-activated myosin ATPase in the same conditions as used for microscopy, and found that the ATPase activity depended both on pCa and on the temperature considerably less than the movement of regulated actin. The results suggest that the sliding velocity in the in vitro system would not be proportional to the rate of actin-activated ATPase.
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PMID:Calcium-triggered movement of regulated actin in vitro. A fluorescence microscopy study. 252 55

The relation between functional properties of the contractile apparatus, such as shortening velocity and ATPase activity, and myosin isoenzyme composition was studied in ventricular myocardium of adult (60-90-day-old) rats and of newborn (3-day-old) and young (10- and 20-day-old) rats. In adult animals, variations of isomyosin pattern were produced by reducing food intake and by changing the thyroid state. Hyperthyroidism was induced with triiodothyronine daily injection for 15 days; hypothyroidism was induced with iodine-free diet and KClO4 in drinking water for 50-60 days. The following parameters were studied: 1) calcium-magnesium-activated and magnesium-activated ATPase activity of washed and purified myofibrils, 2) calcium-activated ATPase activity of purified myosin, 3) isomyosin composition and relative content of alpha-myosin heavy chains (alpha-MHCs), and 4) force-velocity curve of left and right ventricle papillary muscles. To take into account the difference in excitation-contraction coupling between newborn and adult myocardium, the determination of the force-velocity curve was repeated in Krebs' solution with normal [CaCl2] (2.5 mM) and in Krebs' solution with high [CaCl2] (10 mM). During postnatal growth, the relative content of alpha-MHC increased and reached a maximum at about 20 days. Pronounced increases of myofibrillar and myosin ATPase activity and in shortening velocity occurred during the same period. In adult hyperthyroid rats, alpha-MHC content as well as enzymatic activity and shortening velocity were higher than in control adult animals. Hypothyroidism and food deprivation caused a decrease of alpha-MHC content and a reduction of both enzymatic activities and shortening velocity. The study of the relations between alpha-MHC relative content and functional parameters showed that 1) in ventricular myocardium of adult rats a linear relation existed between alpha-MHC content and myosin and myofibrillar ATPase activity and shortening velocity, and 2) in newborn and young rat ventricular myocardium, both enzymatic activities and shortening velocity were lower than would have been expected on the basis of the linear relation described above. This latter observation could be accounted for by a variation in specific activity of myosin during postnatal development or by the presence of peculiar isomyosins that cannot be detected with usual electrophoretic techniques.
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PMID:Shortening velocity and myosin and myofibrillar ATPase activity related to myosin isoenzyme composition during postnatal development in rat myocardium. 252 95

1. The effect of transplasmalemmal Ca2+ influx on the [Ca2+]i dependence of smooth muscle contraction was evaluated by measuring intracellular [Ca2+] (as estimated by aequorin), myosin phosphorylation, and isometric stress in swine carotid media. 2. Extracellular Ca2+ was removed by incubation in physiological saline with 1 mM-EGTA and no added CaCl2 for 20 min (termed EGTA treatment). In some preparations, intracellular Ca2+ was released by a brief (5 min) histamine stimulation while in this Ca2(+)-free EGTA solution (termed histamine treatment). 3. Restoration of extracellular CaCl2 to EGTA and histamine-treated preparations in the continued presence of histamine was associated with an initial large aequorin light transient. However, this light transient was not initially associated with an increase in myosin phosphorylation or rapid stress development, suggesting that the contractile apparatus was desensitized to aequorin-estimated myoplasmic [Ca2+]. The desensitization was temporary, and resolved by 10 min after restoration of extracellular CaCl2. 4. The light transient observed upon restoration of extracellular CaCl2 was smaller in preparations only EGTA treated when compared to preparations treated with both EGTA and histamine, suggesting that histamine treatment further desensitized the contractile apparatus. 5. The stress development rate was not slowed when histamine and extracellular CaCl2 were simultaneously added to EGTA-treated preparations, suggesting that the desensitization was only to transplasmalemmal Ca2+ influx (from extracellular CaCl2 readdition), and not intracellular Ca2+ release (from the histamine stimulation). 6. In EGTA and histamine-treated preparations, restoration of extracellular CaCl2 in the presence of 109 mM-KCl was associated with a larger aequorin light signal than was observed upon readdition of CaCl2 in the presence of histamine, suggesting that depolarization also further desensitized the contractile apparatus. 7. Depolarization of EGTA-treated preparations did not increase [Ca2+] or stress, suggesting that depolarization did not release intracellular Ca2+ stores. 8. No significant light transient was observed upon addition of extracellular LaCl3, suggesting that tissue damage or leakage of aequorin into the extracellular space was not the cause of the Ca2(+)-reintroduction light signal. 9. These data suggest that removal of extracellular CaCl2 desensitizes the contractile apparatus of smooth muscle to transplasmalemmal Ca2+ influx. This desensitization is only to readdition of extracellular Ca2+; the contractile apparatus still responds to intracellular Ca2+ release. The desensitization is increased by prior depolarization or brief histamine treatment (potentially by depleting intracellular Ca2+). The source of activator Ca2+ appears to affect the relationship between aequorin light and phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Desensitization of swine arterial smooth muscle to transplasmalemmal Ca2+ influx. 255 74

Electron microscopy was used to study the structural arrangement of the rod portion of brain myosin under various experimental conditions. At low ionic strength the rod formed spindle-like filaments with continuous 14 nm periodicity. In the presence of KCNS and a high concentration of CaCl2 brain myosin and its rod precipitated in a form of segments displaying both bipolar and unipolar arrangement characteristic of the myosin filaments. Limited proteolytic digestion of the rod with chymotrypsin generated several fragments of molecular masses in the range of 84 kDa to 30 kDa. The 74 kDa fragment appeared to be the shortest one which preserves the ability to form filaments.
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PMID:The assembly of the rod portion of brain myosin. 274

Smooth muscle contraction is dependent on Ca2+ entry from the extracellular space or release from intracellular stores. The sensitivity of these Ca2+ sources to agonist concentration was evaluated by measuring myoplasmic [Ca2+] (as estimated by aequorin), myosin phosphorylation, and isometric stress in the swine carotid media. High histamine concentrations produced transient elevations in [Ca2+] and phosphorylation with rapid generation of near maximal stress. Lower histamine concentrations produced much smaller [Ca2+] and phosphorylation transients, and stress development was slower. Peak [Ca2+] was proportional to the rate of stress development. Steady-state [Ca2+], phosphorylation, and stress values (which are dependent on extracellular Ca2+) were more sensitive to histamine concentration than was the peak [Ca2+] response both in the presence and absence of extracellular CaCl2 (measures of intracellular Ca2+ release). This result suggests that the mechanism for Ca2+ influx from the extracellular space is more sensitive to histamine than intracellular Ca2+ release. These results are also consistent with the hypothesis that agonist-releasable sarcoplasmic reticular Ca2+ is the major contributor to initial phosphorylation transients that enhance the rate of stress development.
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PMID:Histamine concentration and Ca2+ mobilization in arterial smooth muscle. 275 Aug 85

A latent alkaline serine proteinase (ASP) has been extracted from the soluble fraction of lobster claw and abdominal muscles. The enzyme, which was irreversibly activated 30- to 40-fold by brief (2-3 min) heating at 60 degrees C, had an optimal caseinolytic activity at pH 7.75. Its molecular weight was estimated to be 740,000 by gel filtration chromatography. Serine protease inhibitors (diisopropylfluorophosphate, phenylmethanesulfonyl fluoride, soybean trypsin inhibitor, aprotinin, benzamidine, and chloromethyl ketones) suppressed ASP activity 22 to 70%. In addition, sulfhydryl-blocking reagents and hemin inhibited activity 69 to 100%; leupeptin and E-64, however, did not. Pepstatin A, ethylenediaminetetraacetate, and adenosine triphosphate were without effect. These results suggest that the lobster ASP is a serine proteinase that contains one or more sulfhydryl groups essential for catalysis. ASP was stimulated by dithiothreitol and inhibited by CaCl2 and oleic and linoleic acids. The enzyme was partially activated by low concentrations of sodium dodecyl sulfate; 0.05% produced activities 13% of that of preparations heated at 60 degrees C. Neither poly-L-lysine, urea, dimethylsulfoxide, oleic acid, linoleic acid, nor N-ethylmaleimide activated the enzyme. The ASP degraded most myofibrillar proteins, but showed a preferential hydrolysis of paramyosin, troponin-I and -C, and myosin alpha light chain.
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PMID:High-molecular-weight serine proteinase from lobster muscle that degrades myofibrillar proteins. 276 May 71

Depolarization of whole brain synaptosomes, which stimulates transmitter release, also affects regulation of the assembly of actin microfilaments. Lysates of depolarized synaptosomes contain 20% less cytoskeletal actin than lysates of unstimulated synaptosomes. Parameters affecting the assembly of actin are modified before lysis, but release of actin from the Triton-insoluble cytoskeleton does not occur until after lysis. Actin released from the cytoskeleton is not precipitated with myosin, indicating that it consists of monomers and/or short oligomers. Synaptosomes were incubated for 12 sec in one of three solutions of identical ionic strength but of different salt mixtures: 75 mM KCl-2 mM CaCl2, 5 mM KCl-2mM CaCl2, or 75 mM KCl-0.1 mM EGTA. Synaptosomes were then lysed in an F-actin stabilizing buffer containing 1% Triton X-100. Control synaptosomes (no incubation) were lysed directly into the same lysis buffer containing one of the three different salt mixtures. The cytoskeletal and noncytoskeletal actin pools were separated 25 sec after lysis by centrifugation at 10(4) X g for 1 min, and the actin in each pool was quantitated by the DNase I inhibition assay. The drop in cytoskeletal actin induced by depolarization is maximized by including Ca2+ in the depolarizing buffer, and it is blocked completely by adding a neutral thiol protease inhibitor, leupeptin, to either the pre- or post-lysis buffer. The drop is also completely reversed by repolarizing the synaptosomes.
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PMID:Reorganization of actin in depolarized synaptosomes. 286 5

Age related change of the human minor pectoral muscles was biochemically demonstrated. Myosin-ATPase activity was significantly decreased with age, and was activated with Tris. The degree of the activation by Tris was observed to be lower in old aged patients than in the young. Furthermore, at low concentration of CaCl2 (less than 100 microM), myosin-ATPase activity was higher in the young age than in the old, while at high concentration of CaCl2 (more than 1 mM) no significant difference was observed between young and old age. Decrease with age in activation by primary amine such as Tris would play an important role in the muscle working capacity in old age.
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PMID:Age-related change in activation by Tris (hydroxymethyl) aminomethane on myosin-ATPase activity of human minor pectoral muscles. 293 10

1. Purealin, a novel bioactive principle of a sea sponge Psammaplysilla purea, activated the superprecipitation of myosin B (natural actomyosin) from rabbit skeletal muscle. The maximum change in the turbidity increased with increasing purealin concentrations and was three times the control value in the presence of 50 microM purealin. 2. The ATPase activity of myosin B was also elevated to 160% of the control value by 10 microM purealin. On the other hand, purealin inhibited the myosin ATPase in the presence of 10 mM CaCl2 and 0.5 M KCl (Ca2+-ATPase), and the concentration for the half inhibition was 4 microM. 3. On the other hand, purealin activated the myosin ATPase in the presence of 5 mM EDTA and 0.5 M KCl (EDTA-ATPase). The maximum activation by 10 microM purealin was 160% of the control value. 4. Furthermore, similar results concerning the modification of ATPase activities by purealin were obtained in myosin subfragment-1 instead of myosin. 5. These results suggest that purealin activates the superprecipitation of myosin B by affecting the myosin heads directly. It is also an interesting observation that there is a correlation between the activities of the myosin EDTA-ATPase and actomyosin ATPase of myosin B.
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PMID:Purealin, a novel activator of skeletal muscle actomyosin ATPase and myosin EDTA-ATPase that enhanced the superprecipitation of actomyosin. 304 Mar 94

We have purified a polyclonal antibody by affinity chromatography which binds specifically to the phosphorylated form of the regulatory light chain (Mr = 20,000) of smooth muscle myosin. This antibody does not stain relaxed, permeabilized smooth muscle cells isolated from guinea pig taenia coli. However, when these cells were stimulated to contract with CaCl2 (100 microM) and ATP (1 mM), the immunofluorescence staining was localized in a series of transverse bands. This distribution of activated myosin appears to reflect an underlying structural organization of the smooth muscle cell cytoskeleton into mechanically coupled contractile zones.
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PMID:Spatial pattern of myosin phosphorylation in contracting smooth muscle cells: evidence for contractile zones. 306 Apr 69


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