Se. Kurzawa et Ma. Geeves, A NOVEL STOPPED-FLOW METHOD FOR MEASURING THE AFFINITY OF ACTIN FOR MYOSIN HEAD FRAGMENTS USING MU-G QUANTITIES OF PROTEIN, Journal of muscle research and cell motility, 17(6), 1996, pp. 669-676
The dissociation constant for actin binding to myosin and its subfragm
ents (S1 & HMM) is much less than 1 mu M at physiological ionic streng
th. Many of the methods used to measure such affinities are unreliable
for a K-d below 0.1 mu M. We show here that the use of phalloidin to
stablise F-actin and fluorescently labelled proteins allows the affini
ty of actin for myosin S1 to be measured in a simple transient kinetic
assay. The method can be used for K-d's as low as 10 nM and we demons
trate that the K-d's can be estimated using only mu g quantities of ma
terial. Furthermore we suggest how this method may be adapted for ng q
uantities of protein. This will allow the affinity of actin for myosin
fragments to be estimated for proteins which are difficult to obtain
in large quantities i.e. from biopsy material or from proteins express
ed in baculovirus.