Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this study was to determine whether variations of isomyosin expression occurred during doxorubicin-induced cardiomyopathy. A suitable experimental model in which pure delayed cardiotoxic effects could be easily studied was adopted. Young adult female Sprague Dawley rats received 9 mg/kg of doxorubicin (DXR) i.v. divided into three subdoses of 3 mg/kg every third day. Control animals received equal volumes of saline. The animals were examined 9 weeks after treatment. At this time the animals treated with DXR showed ECG alterations, reduction of body weight and a marked decrease of both atrial and ventricular mass, but were still fully hemodynamically compensated. Loss of myofibrillar material could be documented by the reduced recovery of myofibril and myosin. The contractile response of papillary muscles isolated from the right ventricle of treated animals was markedly impaired. Ca-Mg-activated and Mg-activated myofibrillar ATPase activity and Ca-activated myosin ATPase activity were determined on ventricular myocardium of control and treated animals. Both myofibrillar and myosin ATPase activities were found to be significantly reduced. Pyrophosphate gel electrophoresis of purified myosin was carried out. The isomyosin pattern of DXR-treated animals showed a pronounced shift towards V3, the percent of alpha heavy chains being 54.6% in treated rats (80.5% in control rats). This isomyosin shift can explain the reduced myofibrillar and myosin ATPase activity found in treated animals.
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PMID:Reduction of myofibrillar ATPase activity and isomyosin shift in delayed doxorubicin cardiotoxicity. 252 75

The steady-state kinetics of the K+, Ca2+, and Mg2+-activated adenosine triphosphatase (ATPase) activities of rabbit skeletal myosin were investigated in the substrate concentration range from 0.05 microM to 5 mM and found not to follow Michaelis-Menten kinetics but rather to display biphasic behavior. The Ca2+-ATPase activity of myosin chymotryptic subfragment-1 (S-1), which has only one active site, also exhibits biphasic kinetics, thus excluding the possibility that the biphasic behavior is caused by negative cooperativity between the two active sites of myosin. Myosin K+ and Mg2+-ATPase are both activated by 5'-adenyl methylenediphosphonate (AdoPP[CH2]P) in a competitive manner at high substrate concentrations; i.e. the maximal velocity observed at high substrate concentrations is independent of the AdoPP[CH2]P concentration. This result provides evidence for substrate activation via binding to a regulatory site. Pyrophosphate inhibits myosin ATPase in a competitive manner at low substrate concentrations and in an uncompetitive manner at high substrate concentrations, with the uncompetitive Ki being smaller than the competitive Ki; i.e. pyrophosphate binds more tightly to the effector site than to the active site.
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PMID:Biphasic steady-state kinetics of myosin adenosine triphosphatase. Evidence for a substrate effector site. 610 32

Changes in enzymatic and structural properties of ventricular myosin in thyrotoxic rabbit hearts have been investigated extensively. However, there is little information regarding the effect of thyroid hormone on the atrial myosin. In this study, we have compared enzymatic and structural changes of ventricular and atrial myosin from euthyroid, hypothyroid, and hyperthyroid rabbits. In euthyroid rabbits, Ca++- and actin-activated ATPase activities of atrial myosin were 2-fold greater than those of the ventricular myosin. The Ca++- and actin-activated ATPase activities of atrial myosin from hypothyroid and hyperthyroid rabbits were identical with the values for atrial myosin from euthyroid rabbits. The same ATPase activities of ventricular myosin decreased in hypothyroid hearts but increased in hyperthyroid rabbits. The K+ (EDTA)-ATPase activities of all myosins were the same, irrespective of the thyroid status of the animal. Pyrophosphate-polyacrylamide gel electrophoresis patterns showed two isoenzymes (designated as A1 and A3) of atrial myosin in euthyroid hearts. The same electrophoretic patterns also showed in atrial myosin from hypothyroid and hyperthyroid hearts. The ventricular myosin from euthyroid hearts also exhibited two isoenzymes (designated as V1 and V3) but each with slower electrophoretic mobilities than the corresponding atrial myosin. In hypothyroid hearts, only V3 isoenzyme was seen, whereas, in hyperthyroid hearts, only V1 isoenzyme was seen. These results suggest that thyroid hormone controls ventricular myosin ATPase activity by controlling synthesis of a specific ventricular isoenzyme, whereas thyroid hormone does not affect atrial myosin ATPase, possibly due to its inability to control atrial myosin synthesis.
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PMID:Comparative studies of atrial and ventricular myosin from normal, thyrotoxic, and thyroidectomized rabbits. 629 27