The use of actin labelled with N-(1-pyrenyl)iodoacetamide to study the interaction of actin with myosin subfragments and troponin/tropomyosin

Abstract

1. A pyrene label attached to Cys-374 of actin has been shown to be a useful probe for monitoring the interaction of actin with myosin subfragments [Kouyama and Mihashi (1981) Eur. J. Biochem. 114, 33-38]. We report that the presence of this label decreases the affinity of actin for myosin subfragment 1 by less than a factor of 2. The rate of actin binding is unaffected by the label and the dissociation rate is increased by up to a factor of 2. 2. Both the rate of actin binding to, and the rate of actin dissociation from, heavy meromyosin show two phases when monitored by pyrene fluorescence. 3. Thin filaments reconstituted from pyrene-labeled actin show a 5% increase in pyrene fluorescence on binding Ca2+.