J. Biol. Chem., Vol. 267, Issue 20, 13924-13927, 07, 1992
Gelsolin binds to polymeric actin at a low rate
B Schoepper and A Wegner
Institute of Physiological Chemistry, Ruhr-University Bochum, Federal Republic of Germany.
Association of gelsolin with actin filament subunits was investigated by
the decrease of the fluorescence intensity of a 7-nitro-2-oxa-1,3- diazole
(NBD) label covalently linked to gelsolin. The rate constant of this
reaction was found to be 4 x 10(3) M-1 s-1. Binding of NBD-labeled gelsolin
to monomeric actin proceeds at a similar low rate. The rate of association
of gelsolin that was unmodified to actin filament subunits was estimated
too. Unmodified gelsolin was added to a mixture of actin filaments and
actin-DNase I complex. The fractions of gelsolin that bound to actin
filament subunits or to actin-DNase I complex depended on the relative
rates of these two competing reactions. In this way it was possible to
estimate the rate constant of association of unmodified gelsolin with actin
filament subunits (2 x 10(4) M-1 s-1). Thus, gelsolin associates with actin
filament subunits at a rate that is considerably slower than
diffusion-controlled and similar to the rate of binding of gelsolin to
monomeric actin.