| Budget Amount *help |
¥6,000,000 (Direct Cost: ¥6,000,000)
Fiscal Year 1988: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1987: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1986: ¥3,800,000 (Direct Cost: ¥3,800,000)
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| Research Abstract |
1. Paratropomyosin inhibited the Mg-ATPase activity and enhanced K-ATPase activity of myofibrils stoichiometrically, and its maximal binding to actin was estimated to occur at a molar ratio of 1:13. These results indicate that paratropomyosin is able to bind to thin filaments of myofibrils, and that due to its greater affinity for the myosin binding site on actin, paratropomyosin competes for the binding site and helps weaken rigor linkages formed between actin and myosin.
2. Intact myofibrils stained with fluorescent antibodies against paratropomyosin showed that paratropomyosin was exclusively located at the A-I junction of sarcomeres. In stretched myofibrils (3.7 mum in sarcomere length), the approximate width of the fluorescent stripes and their relation to the A band remained constant. During postmortem storage of muscles, on the other hand, paratropomyosin was translocated from its original position at the A-I junction onto thin filaments. The translocation of paratropomyosin was
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successfully induced with a calcium ion concentration of 0.1 mM in the presence of protease inhibitors.
3. The rigor tension of glycerinated fibers was reduced to about 65% of the initial value within 10 min after the addition of purified paratropomyosin, whereas it remained constant for at least 3.5 hr in control fibers. Paratropomyosin showed a stronger effect on the increase in sarcomere length of passively stretched fibers, which developed weaker tensions. The most successful rigor solution contained 0.2-0.25 M KC1, pH 5.5, at 5-10゜C. Under these conditions, which coincide well those of postmortem muscles, the sarcomere length was easily increased from 2.4 to 3.6 mum, if rigor-contracted fibers were passively stretched after the addition of purified paratropomyosin. We therefore conclude that in postrigor muscles, paratropomyosin is released from the A-I junction region following the increase in the sarcoplasmic calcium ion concentration to 0.1 mM, and then binds to thin filaments, which results in weakening of rigor linkages formed between actin and myosin. Less
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