Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Tropomyosin, one of the regulatory proteins in muscle contraction, was prepared from chickens, rabbits, frogs, shrimps, and shellfish, and conserved characteristics were studied using an enzymological technique. 2. All tropomyosins tested, irrespective of their sources, were found to have the ability to mediate the inhibitory activity of rabbit troponin toward rabbit Mg2+-activated actomyosin ATPase (Mg2+-ATPase) activity in the absence of Ca2+ ions. 3. The effect of tropomyosin on the Mg2+-ATPase activity in the presence of Ca2+ ions varied, depending on the source, and this variation appeared to reflect the evolutionary course of this protein. 4. Tropomyosin from shellfish adductor muscle had the ability to bind to rabbit skeletal muscle troponin and actin. This ability is also considered to be a basic characteristic of tropomyosin which has been conserved during evolution.
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PMID:The functional characteristics conserved in tropomyosins. 14 70

The influence of various factors on the interaction of phosphorylated and dephosphorylated myosin with actin was examined. It was found that the difference between the values of specific activity of the two myosin forms of actin-stimulated Mg2+-ATPase is affected by changes in KCl, MgATP and actin concentration. The effect of increased pH on the differences in the rate of ATP hydrolysis by actomyosin containing phosphorylated myosin as compared with that of the dephosphorylated one, observed in the presence of EGTA, is abolished by addition of Ca2+. Tropomyosin strongly inhibits the actin-stimulated Mg2+-ATPase of phosphorylated myosin (by about 60%). The tropomyosin-troponin complex and native tropomyosin lowered the rate of ATP hydrolysis by actomyosin containing both phosphorylated and dephosphorylated myosin by about of 60% of the value obtained in the absence of those proteins. These results indicate that the change of negative charge on the myosin head due to phosphorylation and dephosphorylation of myosin light chains modulates the actin-myosin interaction at different steps of the ATP hydrolysis cycle. Phosphorylation of myosin seems to be a factor decreasing the rate of ATP hydrolysis by actomyosin under physiological conditions.
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PMID:Factors influencing interaction of phosphorylated and dephosphorylated myosin with actin. 293 57

Effects of regulatory proteins on the actomyosin subfragment 1 (acto-S1) Mg2+-ATPase activity were studied over a range of S1 concentration at low actin concentration such that the specific activity was constant in the absence of the regulatory proteins. In their presence, the activity was inhibited at low [S1] and activated at higher [S1] in each of three cases: 1) troponin + tropomyosin + Ca2+; 2) tropomyosin; 3) troponin + tropomyosin - Ca2+. The [S1] required to activate increased in the order 1, 2, 3. In all three cases, however, the inhibition increased toward 100% when the [S1] approached zero. Tropomyosin titrations of acto-S1 ATPase at low [S1] which resulted in inhibition were hyperbolic and gave a binding constant of K approximately 10(7) M-1. In contrast, at higher [S1], tropomyosin titrations were sigmoidal, indicating cooperative effects on activation. These results suggest a modification of the simple steric blocking theory of regulation, in which it is postulated that both of the Ca2+-dependent positions of tropomyosin on the thin filament block the formation of active acto-S1-nucleotide intermediates at low [S1], and in which tropomyosin occupies a third "nonblocking" position in the active state at high [S1]. In this modified model, Ca2+ facilitates the binding of myosin heads, leading to the active site.
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PMID:Dual effects of tropomyosin and troponin-tropomyosin on actomyosin subfragment 1 ATPase. 612 7