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Schlagwörter:
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Zusammenfassung:
In highly purified muscle fibrils and actomyosin preparations P1 is exchanged between AD32P and ATP. The rate of exchange in fibrils is about 0.01 μmole P1/mg protein/min at 0° and 0.05 μmole at 20° if the ionic strength is 0.04 μ and the concentrations of ADP and ATP are 5·10−3M. In actomyosin solutions the rate of exchange is about 0.02 μmole at 0° and at 20° about 0.07 μmole P1/mg protein/min. These values are reliably reproducible.
2.
At 0° the rate of exchange is measured without error at all ionic strengths. At 20° correct values are obtained at an ionic strength of ≧ 0.4 μ.
3.
The phosphate exchange by the amount of granules contained in 1 g of muscle is about 6–9 times as great as the phosphate exchange by the amount of fibrils or actomyosin contained in 1 g of muscle.
4.
The rate of exchange by 1 mg of protein is in granules 30–50 times as great (according to the kind of preparation) as in the highly purified fibrils and actomyosin solutions.
5.
On the other hand, the dependence of the rate of exchange on the concentrations of ATP, ADP, Mg2+, Ca2+ and oxarsan is quantitatively identical for granules, fibrils, and actomyosin solutions but very different from the kind in which the ATPase of the contractile proteins depends on the above mentioned factors.
6.
The observations 4. and 5. suggest to regard the phosphate exchange by fibrils and actomyosin solutions as a phosphate exchange produced by contaminating granule protein. To this end an amount of 2 g granule protein contained in 100 g of the total protein would be sufficient.
7.
It is shown that the difference of the salyrgan effect on the phosphate exchange produced by actomyosin preparations on the one hand and on the exchange produced by granules on the other hand does not present a stringent argument against the conclusion under 6.
