EFFECT OF BOUND-NUCLEOTIDE SUBSTITUTION ON PROPERTIES OF F-ACTIN

F-actins have been prepared in which the bound adenosine nucleotide has been replaced by inosine or cytidine nucleotide, and their properties have been studied. The intrinsic viscocity of IDP-containing F-actin was the same as that of ADP-containing F-actin, but the intrinsic viscosity of CDP-containing F-actin was about half this value. There were no differences in the myosin-binding affinities of the three types of F-actin or in their ability to activate the magnesium-ATPase of myosin. On the other hand, the exchangeability of the F-actin-bound nucleotide, both in the presence and in the absence of myosin, was dependent on the type of bound nucleotide in the actin, increasing in the order IDP<ADP<CDP. Furthermore, under conditions of partial polymerization, actin containing bound inosine nucleotide polymerized faster and to a greater extent than actin containing bound adenosine nucleotide. These results suggest that the bound nucleotide may influence the interaction between monomers in the F-actin polymer. © 1969.