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  • 1
    Electronic Resource
    Electronic Resource
    Subunit function in cardiac myosin: effect of removal of Lc2 (18,000 molecular weight) on enzymic properties (1979)
    s.l. : American Chemical Society
    Biochemistry 18 (1979), S. 461-467 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00570a013
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  • 2
    Electronic Resource
    Electronic Resource
    Calcium regulation in the human myocardium affected by dilated cardiomyopathy: A structural basis for impaired Ca2+-sensitivity (1999)
    Springer
    Molecular and cellular biochemistry 194 (1999), S. 301-313 
    Details
    ISSN: 1573-4919
    Keywords: ATPase activity ; cardiomyopathy ; heart failure ; myosin light chains ; troponin-tropomyosin ; mekratin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Calcium regulation in the human heart is impaired during idiopathic dilated cardiomyopathy (IDC). Here, we analyze the structural basis for impairment in the regulatory mechanism. Regulation of contractility was monitored by MgATPase and Ca2+-binding assays as a function of calcium. Myofibrillar proteolysis and expression of troponin T isoforms were established by gel electrophoresis and by Western blots. Myofibrillar ATPase assays in low salt however, revealed a drastic lowering of calcium sensitivity in IDC myofibrils as indicated by reductions in both activation by high calcium and in EGTA-mediated inhibition of MgATPase. Structural changes in myofilament proteins were found in most IDC hearts, specifically proteolysis of myosin light chain 2 (LC2), troponin T and I (TnT and TnI), and sometimes large isoform shift in TnT. IDC did not induce mutations in LC2 and troponin C (TnC), as established by cDNA sequence data from IDC cases, thus, calcium binding to IDC myofibrils was unaffected. Reassociation of IDC myofibrils with native LC2 raised MgATPase activation at high Ca2+ to control levels, while repletion with intact, canine TnI/TnT restored inhibition at low Ca2+. A model, identifying possible steps in the steric blocking mechanism of regulation, is proposed to explain IDC-induced changes in Ca2+-regulation. Moreover, shifts in TnT isoforms may imply either a genetic or a compensatory factor in the development and pathogenesis of some forms of IDC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006980405359
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  • 3
    Electronic Resource
    Electronic Resource
    Age-related difference in cardiac adaptation to chronic hypertension in rats, with and without nifedipine treatement (1999)
    Springer
    Molecular and cellular biochemistry 198 (1999), S. 109-112 
    Details
    ISSN: 1573-4919
    Keywords: LVH ; hypertension ; aging ; myosin isozyme ; nifedipine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Three myosin isozymes, V1 (αα MHC = Myosin Heavy Chain gene), V2 (αβ MHC) and V3 (ββ MHC) that are identified in the cardiac ventricles of most mammals have been shown to shift to a V3 predominance pattern during cardiac growth and in response to left ventricular pressure overload, and to V1 predominance following anti hypertensive treatment. This study examined whether long-term hypertension impairs the ability of the adult heart to restructure myosin isozyme proportions. Using pyrophosphate gel electrophoresis, we studied proportions of cardiac myosin isozymes (V1 and V3) in young (16 weeks) and adult (36 weeks) spontaneously hypertensive rats (SHR), and following 12 weeks of nifedipine (N) treatment in age-matched SHR rats (SHR-N). The values of V1 and V3 myosin isozymes were derived by adding half of the value of V2 to each isozyme proportion. The V3 proportion in the young SHR control (SHR-C) group (49%) was 34% higher (p 〈 0.05) than in the young Wistar Kyoto control (WKY-C) group (37%). However, the proportion was similarly high, though not statistically significant, in both the adult SHRC (73%) and WKY-C (71%) groups. The proportion in the young SHR-N group (29%) was 41% lower (p 〈 0.05) than in the young SHR-C group (49%), and the proportion in the adult SHR-N group (47%) was 34% lower (p 〈 0.05) than in the adult SHR-C group (73%). The ratio of left ventricular weight to body weight (LVW/BW), which determines left ventricular hypertrophy (LVH), was higher in both young and adult SHR-C (26%, p 〈 0.05, and 42%, p 〈 0.05, respectively) than in WKY-C groups. The mean LVW/BW was 27% (p lt; 0.05) greater in adult than in young SHR-C rats. The LVW/BW in both age groups of treated SHR-N was similar to that in age matched WKY-C rats. Conclusion: Our study showed that a rise in the V3 level occurs in young hypertensive rats, but no rise occurs in the V3 level in adult hypertensive rats. High blood pressure seems to contribute to the high V3 level in young hypertensive rats, but in adult hypertensive rats, high blood pressure does not accentuate the V3 rise already acquired due to the aging process. Nifedipine treatment in both young and adult hypertensive rats prevented the V3 rise due to hypertension and to the aging process. This effect of nifedipine seems to be through its antihypertensive action.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006968011206
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  • 4
    Electronic Resource
    Electronic Resource
    Role of regulatory proteins (troponin-tropomyosin) in pathologic states (1994)
    Springer
    Molecular and cellular biochemistry 135 (1994), S. 43-50 
    Details
    ISSN: 1573-4919
    Keywords: contractile proteins ; regulatory proteins complex ; troponin ; tropomyosin ; actin ; myosin ; myofibrils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In vertebrate striated muscle, troponon-tropomyosin is responsible, in part, not only for transducing the effect of calcium on contractile protein activation, but also for inhibiting actin and myosin interaction when calcium is absent. The regulatory troponin (Tn) complex displays several molecular and calcium binding variations in cardiac muscles of different species and undergoes genetic changes with development and in various pathologic states. Extensive reviews on the role of tropomyosin (Tm) and Tn in the regulation of striated muscle contraction have been published describing the molecular mechanisms involved in contractile protein regulation. In our studies, we have found an increase in Mg2+ ATPase activity in cardiac myofibrils from dystrophic hamsters and in rats with chronic coronary artery narrowing. The abnormalities in myofibrillar ATPase activity from cardiomyopathic hamsters were largely corrected by recombining the preparations with a TnTm, complex isolated from normal hamsters indicating that the TnTm, may play a major role in altered myocardial function. We have also observed down regulation of Ca2+ Mg2+ ATPase of myofibrils from hypertrophic guinea pig hearts, myocardial infarcted rats and diabetic-hypertensive rat hearts. In myosin from diabetic rats, this abnormality was substantially corrected by adding troponin-tropomyosin complex from control hearts. All of these disease models are associated with decreased ATPase activities of pure myosin and in the case of rat and hamster models, shifts of myosin, heavy chain from alpha to beta predominate. In summary, there are three main troponin subunit components which might alter myofibrillar function however, very few direct links of molecular alterations in the regulatory proteins to physiologic and pathologic function have been demonstrated so far.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00925959
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  • 5
    Electronic Resource
    Electronic Resource
    Troponin subunits contribute to altered myosin ATPase activity in diabetic cardiomyopathy (1995)
    Springer
    Molecular and cellular biochemistry 151 (1995), S. 165-172 
    Details
    ISSN: 1573-4919
    Keywords: myosin ; regulatory proteins ; troponin I ; troponin T ; diabetic cardiomyopathy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Our group has documented that myocardial performance is impaired in the hearts of chronically diabetic rats and rabbits. Abnormalities in the contractile proteins and regulatory proteins may be responsible for the mechanical defects in the streptozotocin (STZ)-diabetic hearts. Previously, the major focus of our research on contractile proteins in abnormal states has concentrated on myosin ATPase and its isoenzymes. Our present study is based on the overall hypothesis that regulatory proteins, in addition to contractile protein, myosin contribute to altered cardiac contractile performance in the rat model of diabetic cardiomyopathy. The purpose of our research was to define the role of cardiac regulatory proteins (troponin-tropomyosin) in the regulation of actomyosin system in diabetic cardiomyopathy. For baseline data, myofibrillar ATPase studies were conducted in the myofibrils from control and diabetic rats. To focus on the regulatory proteins (troponin and tropomyosin), individual proteins of the cardiac system were reconstituted under controlled conditions. By this approach, myosin plus actin and troponin-tropomyosin from the normal and diabetic animals could be studied enzymatically. The proteins were isolated from the cardiac muscle of control and STZ-diabetic (4 weeks) rats. Sodium dodecyl sulfate gel electrophoretic patterns demonstrate differences in the cardiac TnT and TnI regions of diabetic animals suggesting the different amounts of TnT and/or TnI or possibly different cardiac isozymes in the regulatory protein complex. Myofibrils probed with a monoclonal antibody TnI-1 (specific for adult cardiac TnI) show a downregulation of cardiac TnI in diabetics when compared to its controls. Enzymatic data confirm a diminished calcium sensitivity in the regulation of the cardiac actomyosin system when regulatory protein(s) complex was recombined from diabetic hearts. Actomyosin ATPase activity in the hearts of diabetic animals was partially reversed when myosin from diabetic rats was regulated with the regulatory protein complex isolated from control hearts. To our knowledge, this is the first study which demonstrates that the regulatory proteins from normal hearts can upregulate cardiac myosin isolated from a pathologic rat model of diabetes. This diminished calcium sensitivity along with shifts in cardiac myosin heavy chain (V1→V3) may be partially responsible for the impaired cardiac function in the hearts of chronic diabetic rats. (Mol Cell Biochem151: 165–172, 1995)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322339
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  • 6
    Electronic Resource
    Electronic Resource
    Expression and regulation of mutant forms of cardiac TnI in a reconstituted actomyosin system: Role of kinase dependent phosphorylation (1997)
    Springer
    Molecular and cellular biochemistry 170 (1997), S. 99-107 
    Details
    ISSN: 1573-4919
    Keywords: troponin I ; protein kinase A ; protein kinase C ; actomyosin ATPase ; TnI mutant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract When phosphorylated, the inhibitory subunit of troponin (TnI) causes a loss in calcium sensitivity and a decrease in actomyosin ATPase. To examine this process, we bacterially expressed wild type TnI and TnI mutants in which serine 22 and 23, a putative protein kinase A (PKA) site, and threonine 143, a putative protein kinase C (PKC) site, were replaced by alanine S22A/23A and T143A. PKA dependent phosphorylation was ~90% reduced in the S22A/23A mutant and unaffected in T143A. PKC dependent phosphorylation was markedly reduced in T143A relative both to a wild type construct and to S22A/23A, although some residual phosphorylation (likely at sites other than T143) was seen. The calcium sensitivity (i.e. inhibition of actomyosin ATPase in the presence of EGTA) and regulation of the reconstituted actomyosin system was preserved in the absence of phosphorylation using wild type TnI or either mutant. Calcium sensitivity was decreased by both PKA and PKC with the wild type TnI but was unaffected by PKA when the S22A/23A mutant was employed and by PKC when the T143A mutant was reconstituted. The calcium dependency of the ATPase curve was substantially right shifted when PKC phosphorylated wild type TnI was employed for regulation, and this was markedly attenuated when T143 A was reassociated (although a slight rightward shift and a reduction in maximal ATPase activity was still seen). These data confirm that phosphorylation of TnI by regulatory kinases plays a major role in the regulation of myofibrillar ATPase. The N-terminal serines (22 and 23) appear to be uniquely important for the PKA response whereas threonine 143 is involved in the PKC response although other residues may also have functional significance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006865600519
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  • 7
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    PKC? inhibits the hyperglycemia-induced apoptosis signal in adult rat ventricular myocytes (2005)
    Springer
    Details
    Publication Date: 2005-01-01
    Print ISSN: 0300-8177
    Electronic ISSN: 1573-4919
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Published by Springer
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  • 8
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    Troponin subunits contribute to altered myosin ATPase activity in diabetic cardiomyopathy (1995)
    Springer
    Details
    Publication Date: 1995-10-01
    Print ISSN: 0300-8177
    Electronic ISSN: 1573-4919
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Published by Springer
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  • 9
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    Role of regulatory proteins (troponin-tropomyosin) in pathologic states (1994)
    Springer
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0300-8177
    Electronic ISSN: 1573-4919
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Published by Springer
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  • 10
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    Subunit function in cardiac myosin: effect of removal of Lc2 (18,000 molecular weight) on enzymic properties (1979)
    American Chemical Society
    Details
    Publication Date: 1979-02-06
    Print ISSN: 0006-2960
    Electronic ISSN: 1520-4995
    Topics: Biology , Chemistry and Pharmacology
    Published by American Chemical Society
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