Abstract
The study was made of the effect of various concentration of ATP on the solubility of actomyosin in the low concentration of KCl at pH 7, in order to confirm the possiblility that ATP may also produce the “phenomenon of dual precipitation” which has been observed with Na-pyrophosphate and to clarify the relation of the phenomenon to the superprecipitation.
The results obtained are as follows:
(1) In the lower concentration of KCl at pH the solubility of actomyosin fails to run parallel with the increase of ATP concentration, but it shows dual decrease in the interim (the “phenomenon of dual precipitation” produced by ATP); one decrease appears at 10-6M of ATP, the other in the range of the concentration from 10-5M to 5×10-3M.
(2) The precipitate at higher concentration of ATP occurs after going through a state of high solubility (clear phase) and is accompanied with syneresis (superprecipitation), while the precipitate at lower concentration of ATP is formed immediately after the set-out of the reaction and is not accompanied with syneresis.
(3) In this case it is noted that the condition under which the precipitate at higher ATP concentration appears is in agreement with that under which ATPase activity is highest.
(4) The mechanism of the “phenomenon of dual precipitation” produced by ATP has been discussed in detail. From this discussion, the occurrence and the grade of the syneresis is closely related not only to activity of ATPase but also to the extent of the discharge of actomyosin molecule which is considered to take place owing to its combination with ADP and inorganic phosphate (or one of these) which are produced from ATP by the action of actomyosin-ATPase.
