Fluorescence changes of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole bound to thiol groups of gizzard myosin.

The fluorescence intensity of gizzard myosin that incorporated about 2 mol of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-C1) at 0.6 M KC1 was quenched at low concentrations of MgATP or in the presence of F-actin. The observed quenching was reduced at high MgATP concentrations. The half maximal change in quenched fluorescence was shifted from 7.5 microM to 25 microM MgATP for NBD-myosin at 0.15 M KC1. The fluorescent label NBD-C1 can be used to detect changes in the conformation of gizzard myosin.