Abstract
1. Practically the entire granule fraction which inhibits ATP-splitting and contraction is precipitated from crude rabbit-muscle extract by centrifuging at 25,000 × g for 1 h. The diameter of the granules in this fraction is about 1000 Å (700–3000 Å).
2.
2. The activity of the granules is irreversibly destroyed by SH-reagents, thymol and u.v. light. Inhibition caused by certain detergents, e.g. antarox is partially reversible.
3.
3. The activity of the granules is irreversibly lost when the granules are digested with several times their weight of trypsin in the absence of ATP, but is not affected when ATP is present.
4.
4. Before they can produce inhibition, the granules must be activated by ATP and Mg in the absence of Ca. Activation takes only a few minutes, and occurs normally during the experiments themselves.
5.
5. The inhibition of ATP splitting and contraction of fibrils or actomyosin floccules produced by the granules ceases as soon as the granules are removed.
6.
6. Thus, the granules do not withdraw any functionally essential substances from the contractile proteins, nor do they release any stable contraction-inhibiting substance to the actomyosin or to the solution.
7.
7. Over a wide concentration range, the effect of the granules does not depend on their absolute concentration, but on the granule/fibril ratio, in spite of the fact that the granules are not bound to the fibrils. Hence, the granules can not be identical with the inhibitor which reacts directly with the actin- and myosin-filaments.
8.
8. It seems probable, however, that the granules release a labile inhibitor, since their relaxing effect can be exhausted by repeated washing with fibril suspensions. During such washings, the fibrils remove no granules, but merely take away their activity.
9.
9. It is shown that all relaxing and inhibiting effects of the granules in actomyosin gels are brought about only by dissociation of the actomyosin in the presence of ATP and granules. The L-myosin-ATPase as well as the ability for and the state of polymerisation of the actin are not affected by the relaxing granules.
1. Practically the entire granule fraction which inhibits ATP-splitting and contraction is precipitated from crude rabbit-muscle extract by centrifuging at 25,000 × g for 1 h. The diameter of the granules in this fraction is about 1000 Å (700–3000 Å).
2.
2. The activity of the granules is irreversibly destroyed by SH-reagents, thymol and u.v. light. Inhibition caused by certain detergents, e.g. antarox is partially reversible.
3.
3. The activity of the granules is irreversibly lost when the granules are digested with several times their weight of trypsin in the absence of ATP, but is not affected when ATP is present.
4.
4. Before they can produce inhibition, the granules must be activated by ATP and Mg in the absence of Ca. Activation takes only a few minutes, and occurs normally during the experiments themselves.
5.
5. The inhibition of ATP splitting and contraction of fibrils or actomyosin floccules produced by the granules ceases as soon as the granules are removed.
6.
6. Thus, the granules do not withdraw any functionally essential substances from the contractile proteins, nor do they release any stable contraction-inhibiting substance to the actomyosin or to the solution.
7.
7. Over a wide concentration range, the effect of the granules does not depend on their absolute concentration, but on the granule/fibril ratio, in spite of the fact that the granules are not bound to the fibrils. Hence, the granules can not be identical with the inhibitor which reacts directly with the actin- and myosin-filaments.
8.
8. It seems probable, however, that the granules release a labile inhibitor, since their relaxing effect can be exhausted by repeated washing with fibril suspensions. During such washings, the fibrils remove no granules, but merely take away their activity.
9.
9. It is shown that all relaxing and inhibiting effects of the granules in actomyosin gels are brought about only by dissociation of the actomyosin in the presence of ATP and granules. The L-myosin-ATPase as well as the ability for and the state of polymerisation of the actin are not affected by the relaxing granules.
