Phalloidin reduces the release of inorganic phosphate during actin polymerization.

Phalloidin, an actin-filament stabilizing peptide from Amanita phalloides, did not inhibit ATP hydrolysis during actin polymerization but strongly retarded the release of the hydrolysis product Pi. Thus, the lifetime of the intermediate F-actin-ADP-Pi is significantly increased by phalloidin. The results suggest a close correlation between filament stability and F-actin-ADP-Pi intermediates.