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Abstract

1. The effects of various-SH group reagents and of some other agents on chracteristic properties of l-myosin and actomyosin has been studied. 2. 2. Different -SH group reagents, when blocking the ATPase activity of l-myosin, also destroy its reaction with actin. 3. 3. Actomyosin, treated with the same reagents under the same conditions, loses its ATPase activity even when it is not dissociated into l-myosin and actin. 4. 4. l-Myosins which react perfectly with actin but show no ATPase activity either in the absence or presence of actin can be isolated from iodoacetamide-treated actomyosins. 5. 5. These findings suggest that the combining sites of l-myosin with ATP and with actin are not the same. 6. 6. The protection of some -SH group(s) of l-myosin by actin indicates that sulfhydryl groups are somehow involved in the myosin-actin binding. 7. 7. When blocking the ATPase activity of actomyosin, the -SH group reagents also diminish the dissociating effect of ATP on actomyosin; this inhibition of the dissociation is exhibited by the l-myosin component of actomyosin. 8. 8. It is shown that blocking some -SH groups of l-myosin in actomyosin reduces the high affinity of actomyosin for ATP to the low level for pyrophosphate. 9. 9. It is assumed that the “pyrophosphate-binding part” of l-myosin participates in the interaction with ATP and with actin. 10. 10. Binding the -NH2 groups of actomyosin—with N-carboxy-cysteine anhydride—inhibits completely its ATPase activity, although the net anionic charge of the protein is not increased. 11. 11. Neutralization of the free carboxylic groups of actomyosin or l-myosin—by excess polylysine—does not affect the Ca activated ATPases; Mg activated actomyosin ATPase in gel is, however, strongly inhibited by polylysine.