Abstract
The sequence of reactions involved in the polymerization of ATP-actin and accompanying hydrolysis of ATP has been investigated by using a new glass-fiber filter assay. The assay allows the rapid separation of filaments from monomeric actin, and therefore the straightforward identification of the nucleotide bound to F-actin in the time course of polymerization, using double-labeled [gamma-32P,3H]ATP. The data bring a direct confirmation of the existence of the previously proposed ATP-F-actin intermediate in the time course of polymerization. Moreover, comparison of the hydrolyzed ATP (i.e., acid-labile [32P]Pi) and of 32P bound to F-actin provides direct evidence for the second intermediate ADP-Pi-F-actin in the polymerization process. This latter species is the major transient in the polymerization of ATP-actin, its lifetime being of the order of minutes.
Published Version
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