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: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ca2+ regulation of molluscan actomyosin adenosine triphosphatase is known to be associated with the myosin molecule. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, however, also suggests the possible presence of troponin, a thin-filament-linked Ca2+-regulatory complex. In the present study, scallop troponin and tropomyosin were prepared and complexed with rabbit actin; the resulting synthetic thin filaments form a Ca2+-dependent actomyosin adenosine triphosphatase with Ca2+-insensitive rabbit myosin, indicating that the troponin in scallops is potentially functional. Scallop troponin I was isolated and mixed with chicken troponin C and troponin T, forming a functional hybrid troponin complex, indicating that scallop and vertebrate troponins may act by a common mechanism. Densitometry of sodium dodecyl sulphate/polyacrylamide gels reveals that in synthetic thin filaments there are larger amounts of troponin than are present in native thin filaments. Amounts present in the intact muscle were not determined.
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PMID:Troponin-like proteins from muscles of the scallop, Aequipecten irradians. 14 88

1. A troponin C-like protein was prepared from frozen chicken gizzard by preparative polyacrylamide gel electrophoresis and its apparent molecular weight was estimated to be about 15,500 daltons. 2. In urea gel electrophoresis, the mobility of the troponin C-like protein increased slightly in the presence of Ca2+, like that of skeletal muscle troponin C. On the other hand, the mobility of the the troponin C-like protein in glycerol gel electrophoresis, unlike that of skeletal muscle troponin C, was significantly decreased by Ca2+. 3. In alkaline gel electrophoresis, the troponin C-like protein formed a Ca2+-dependent complex with troponin I or troponin T from skeletal muscle. 4. The troponin C-like protein could neutralize the inhibitory effect of skeletal muscle troponin I on the Mg2+-activated ATPase of actomyosin from rabbit skeletal muscle, but could not confer Ca2+-sensitivity on the actomyosin in the presence of troponin I and troponin T from skeletal muscle.
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PMID:Troponin C-like protein in chicken gizzard muscle. 15 22

Many neurohormones alter the force of cardiac contraction by variations in the intracellular Ca2+ concentration. alpha 1-Adrenergic and muscarinic stimulations, rather, modify the sensitivity of contractile proteins to Ca(2+)-calmodulin-myosin light-chain kinase (MLCK) complex induces a large increase in Ca2+ sensitivity (0.14 pCa unit) of these easily accessible myofilaments. This increase is further enhanced by up to 0.19 pCa unit when protein kinase C (PKC) is added together with MLCK. Similarly, the Ca2+ ATPase activity of skinned cells in suspension is increased in the presence of MLCK and further in the presence of both kinases. 32P-labelling and SDS/PAGE show that these changes are associated with light-chain 2 (LC2) phosphorylation together with phosphorylation of troponin I and troponin T when PKC is added. Although to a smaller extent than in smooth muscle, phosphorylation of cardiac myosin LC2 may be involved in the modulation of heart contractility.
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PMID:Protein kinase C enhances myosin light-chain kinase effects on force development and ATPase activity in rat single skinned cardiac cells. 138 18

The expression of troponin T, a thin filament regulatory protein, was examined in normal and failing left ventricles. The samples were obtained from the hearts of patients with severe heart failure who were undergoing cardiac transplantation, and from normal adult hearts that could not be used for transplantation. Western blots of the myofibrillar proteins demonstrated two isoforms, troponin T 1 (TnT1) and troponin T 2 (TnT2). TnT2 is expressed at significantly higher levels in failing hearts (p less than 0.004). Western blots of two-dimension SDS-PAGE gels resolved two dominant spots of TnT1 and of TnT2 and several minor troponin T species. Alkaline phosphatase treatment markedly decreased the sizes of the two acidic spots while increasing the two more basic spots by a comparable amount. Myofibrillar ATPase activity had an inverse and negative linear relationship (r = 0.7, p less than 0.02) with the myofibrillar percentage of total troponin T comprised of TnT2. In that heart failure in these transplant patients had multiple bases, we propose that rather than a cause of heart failure, the disease-associated changes in troponin T isoform expression are an adaptation to abnormal myocardial function.
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PMID:Troponin T isoform expression in the normal and failing human left ventricle: a correlation with myofibrillar ATPase activity. 138 29

A 25 kDa fragment of beta-type troponin T (beta-TnT) was expressed in Escherichia coli, and its function as a component of the regulatory system for actomyosin ATPase was compared with that of the authentic counterpart, the full length alpha-TnT. The expressed species, designated as beta-TnT(N'-208), consists of 208 residues. It lacks the entire variable region at the amino-terminus and, near the carboxyl-terminus, a segment of 14 residues is changed from the alpha-type to the beta-type sequence. Functional tests indicated that the truncated beta-TnT was not distinguishable from the full length alpha-TnT, suggesting that neither deletion of the variable N-terminal region nor alteration of the type has a significant effect on the regulatory action of TnT.
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PMID:Expression in Escherichia coli and a functional study of a beta-troponin T 25 kDa fragment of rabbit skeletal muscle. 142 16

The number of specific Ca2+ bound to Akazara scallop troponin C was estimated to be 0.7 with an apparent binding constant of 5 x 10(5) M-1 (T. Ojima and K. Nishita, 1986, J. Biol. Chem. 261, 16749-16754). In the present paper, we report on the Ca(2+)-induced conformational changes in the troponin C and the interaction of the troponin C with rabbit troponin subunits. The Ca2+ binding to the troponin C caused a marked change in difference uv absorption spectra and a retardation of elution on Sephacryl S-200 gel filtration. However, its circular dichroism spectrum was hardly changed by the Ca2+ binding. These results suggest that the Ca2+ binding to the troponin C induced changes predominantly in tertiary structure rather than in secondary structure. Akazara scallop troponin C was shown to be able to bind to rabbit troponin I-Cellulofine affinity column, but the affinity was not greatly increased by Ca2+ unlike the case of rabbit troponin C. On hybridizing with rabbit troponin T and I, Akazara scallop troponin C was shown to be incapable of substituting rabbit troponin C; i.e., the hybrid troponin strongly inhibited the Mg-ATPase activity of rabbit actomyosin-tropomyosin irrespective of the presence or absence of Ca2+, thus recovering no Ca2+ sensitivity.
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PMID:Akazara scallop troponin C: Ca(2+)-induced conformational change and interaction with rabbit troponin subunits. 144 75

We studied changes in myofibrillar function and protein profiles after complete global ischemia with anoxia in rat hearts. Hearts were exposed to global ischemia and anoxia (CGI) for 30 or 60 minutes at 37 degrees C, and myofibrils were prepared for measurement of Ca(2+)-dependent Mg(2+)-ATPase activity at pH 7.0 and 6.5. Hearts incubated in cold saline (1 +/- 1 degrees C) and nonincubated hearts served as controls. Maximum ATPase activity was unchanged at pH 7.0 and pH 6.5 in myofibrils from hearts treated with 30 or 60 minutes of CGI. At pH 7.0, the Hill coefficient, which is an index of cooperative interactions among thin-filament proteins, was unchanged after 30 minutes of CGI but was significantly increased after 60 minutes of CGI. A similar trend for increased cooperativity was observed when myofibrillar ATPase activity was measured at pH 6.5 in myofibrils from rat hearts made ischemic for 30 or 60 minutes. Both 30 and 60 minutes of CGI resulted in increased pCa50 values (half-maximally activating free [Ca2+]) at pH 7.0 and pH 6.5. Densitometric analysis of myofibrillar proteins separated with sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that troponin I and troponin T were degraded during 60 minutes of CGI. Two new protein bands appearing in ischemia-treated myofibrils were identified as partially degraded troponin I and troponin T with Western blots. The troponin I fragment could be phosphorylated by cAMP-dependent protein kinase. In addition, we observed phosphorylation of a protein band that corresponded to myosin light chain-2 in myofibrils from CGI-treated hearts. These results suggest that degradation of thin-filament proteins may contribute to the changes in cooperativity of Ca2+ regulation of ATPase activity observed in the myofibrils from rat hearts exposed to CGI.
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PMID:Alterations in myofibrillar function and protein profiles after complete global ischemia in rat hearts. 153 Nov 86

The Ca(2+)-sensitive ATPase activity of rabbit skeletal myofibrils was desensitized by treatment with excess troponin T and was found to be activated irrespective of the Ca2+ concentrations. A SDS-gel electrophoretic study showed that both troponin C and troponin I were removed from the myofibrils on treatment with troponin T. The Ca(2+)- and Sr(2+)- sensitivities of the ATPase of troponin T-treated myofibrils reconstituted with troponin C. I were the same as in the intact myofibrils. The Ca(2+)-activated ATPase of rabbit skeletal myofibrils was also desensitized on treatment with chicken breast troponin T or its 26K fragment. The SDS-gel electrophoretic study revealed that troponin T, in addition to troponin C and troponin I, was also removed from the myofibrils and, instead, chicken breast troponin T or its 26K fragment was incorporated into the myofibrils. The Ca(2+)- sensitivity of myofibrils treated with chicken breast troponin T or its 26K fragment was then regained on reconstitution with troponin C.I. These findings indicate that the change in composition of myofibrils on treatment with troponin T or its 26K fragment is due to the selective replacement of the troponin C.I.T complex in the myofibrils as a whole with troponin T or its 26K fragment.
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PMID:Replacement of troponin components in myofibrils. 153 75

The binding of the NH2-terminal region of troponin T (TnT) to the COOH-terminal region of tropomyosin (Tm) and the head-to-tail overlap between Tm molecules is thought to provide a pivotal link between troponin (Tn) and Tm (White, S.P., Cohen, C., and Phillips, G.N., Jr. (1987) Nature 325, 826-828). To further explore the structure-function relationship of the NH2-terminal region of TnT, we studied the binding of a 26,000-dalton TnT fragment (26K-TnT, Ohtsuki, I., Shiraishi, F., Suenaga, N., Miyata, T., and Tanokura, M.J. (1984) J. Biochem. (Tokyo) 95, 1337-1342) which corresponds to residues 46-259 of TnT2f, the major isoform of TnT in rabbit fast twitch muscle, to immobilized alpha-Tm. Both 26K-TnT and TnT2f were retained by the alpha-Tm affinity column in the presence of 150 mM NaCl. However, upon increasing the NaCl concentration 26K-TnT was eluted from the column at a higher ionic strength than was TnT. When applied alone, the binary complex of TnI and TnC (TnC.TnI) was not retained by the alpha-Tm affinity column. When applied subsequently to prebound TnT2f or 26K-TnT, TnI.TnC was retained by the alpha-Tm affinity column and eluted together with TnT2f or 26K-TnT as ternary troponin complexes. Whether Ca2+ was present or not, Tn containing 26K-TnT was eluted at a higher ionic strength than was Tn containing TnT2f, indicating that removal of the first 45 residues of TnT2f strengthens the binding of Tn to Tm. In the presence of Tm, reconstituted Tn containing 26K-TnT conferred Ca2+ sensitivity on actomyosin-S1 MgATPase, and the steepness of the pCa-ATPase relation was unchanged with respect to the actoS1 ATPase regulated by TnT2f. It is concluded that the first 45 residues of TnT2f are not essential for anchoring the troponin complex to the thin filament and do not play a crucial role in the cooperative response of regulated actoS1 ATPase to Ca2+.
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PMID:Deletion of the first 45 NH2-terminal residues of rabbit skeletal troponin T strengthens binding of troponin to immobilized tropomyosin. 182 57

cDNA clones encoding two isoforms of chicken gizzard calponin, a recently identified actin- and tropomyosin-binding protein, have been isolated and sequenced. The deduced polypeptides, 292 (Mr 32,333) and 252 (Mr 28,127) amino acids, contain sequences homologous to: a smooth muscle protein SM22 alpha, the Drosophila melanogaster mp20 gene product, troponin T, troponin I, and caldesmon. Calponin mRNAs of approximately 1.3 kilobases, encoding both isoforms, were expressed in all chicken smooth muscle tissues examined. These data, coupled with the inhibition of actomyosin ATPase by calponin (Winder, S. J., and Walsh, M. P. (1990) J. Biol. Chem. 265, 10148-10155; Abe, M., Takahashi, K., and Hiwada, K. (1990) J. Biochem. (Tokyo) 108, 835-838), suggest that calponin may function as a troponin homolog involved in the regulation of thin filament activity.
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PMID:Molecular cloning and sequence analysis of smooth muscle calponin. 207 3


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