EFFECT OF PHALLOIDIN ON THE STABILITY OF F-ACTIN AND G-ACTIN

The effect of the bicyclic heptapeptide toxin phalloidin on the stabil ity of monomeric (G) and polymeric (F) actin was assessed using the in trinsic tryptophan fluorescence of the protein and the fluorescence of the hydrophobic probe bis-ANS. The latter was shown to be sensitive t o actin polymerization. Phalloidin (1-2 molecules per actin molecule) raises the F-actin denaturation temperature by similar to 15 degrees C . Stabilization of F-actin by phalloidin is more pronounced during den aturation with urea. G-Actin also proved to be stabilized by phalloidi n, testifying to their direct interaction.