Effect of troponin and tropomyosin on the interaction between cytochalasin B and actin filaments.

Effects of troponin (TN) components and tropomyosin (TM) on the interactions between actin filament and cytochalasin B (CB) at low ionic strength were investigated using electron microscopy and viscometry. CB decreased the viscosity of the actin filament and this effect became apparent at 10 microM CB and reached the maximum at 40 microM. CB (40 microM) shortened the average actin filament length from 0.50 to 0.25 micrometers as observed electron microscopically. Presence of TN components and TM diminished the effect of CB on both viscosity and filament length. TN-T but not TN-I had an inhibitory effect on the decrease of the viscosity of the A+TM filament induced by CB. TN-T1 but not TN-T2, one of two chymotryptic subfragments of TN-T, had the same inhibitory effect seen with TN-T. Thus, the cooperation between the T1 region of TN-T and TM is probably essential for the inhibitory action on CB-actin interactions.