The Kinetics of the Exchange of G‐Actin‐Bound 1: N6‐Ethenoadenosine 5′‐Triphosphate with ATP as Followed by Fluorescence

Abstract

1: N6‐Ethenoadenosine 5′‐triphosphate (ɛATP), a fluorescent analog of ATP, binds to monomeric actin with a binding constant which is only about 5 times smaller than that of ATP. The spectroscopic changes which occur when ɛATP binds to actin are studied and used to monitor the kinetics of nucleotide exchange. The first‐order rate constant which is measured at a large excess of ATP over ɛATP strongly depends on the ATP and Ca2+ concentrations. This finding is explained by a mechanism in which the nucleotide dissociates much more easily from Ca2+‐free than from Ca2+‐bound actin. Of special interest is the temperature dependence of the dissociation rate constant. The Arrhenius plot shows a sharp bend near 24 °C. Copyright © 1975, Wiley Blackwell. All rights reserved