Interaction between Synthetic ATP Analogues and Actomyosin Systems. IV*

Abstract

The following compounds were synthesized as analogues of ATP: Tubercidin 5′triphosphate (II), 2′ 3′-O-isopropylidene 6-chloro-(9-β-D-ribofuranosyl) purine 5′triphosphate (III) and 2′ 3′O-isopropylidene-6-mercapto-(9-β-D-riboruranosyl) purine 5′triphosphate (IV). The interaction of these analogues with actomyosin systems, together with those of P³-methyl-adenosine 5′triphosphate (I), were investigated. The degrees of decrease in light-scattering of myosin B on the addition of these analogues were similar to that induced by ATP, except in the case of Compound I. The rates of hydrolysis of the analogues by myosin B in 0.6 M KC1 and 7 mM Ca⁺⁺ were in the decreasing order of ATP>IV>II>III>I, while the order of hydrolysis in 0.075 M KC1 and 2 mM Mg⁺⁺ was IIIV>III>ATP>I. Compound I was not hy-drolyzed at all. Compounds II and III induced weak contraction of myofibrils, while Compounds IV and I did not. Our present and previous results together with those of other workers on the interaction between ATP analogues and actomyosin systems were summarized. Analysis of these results has considerably clarified the roles of the three parts of ATP (the base, ribose and triphosphate) in the decrease in light-scattering of myosin B caused by ATP, the hydrolysis of ATP by the myosin-type ATPase reaction and the contraction of myofibrils induced by ATP.