THE IN-VITRO MOTILITY ASSAY AND PHALLOLDIN-F-ACTIN

We have compared the osmotic properties of the hydrated, native actin filament and of hydrated phalloidin-F-actin. We have found that phallo idin-F-actin interacts much more strongly with water than native F-act in. It is therefore very likely that the interaction with myosin (that requires the expulsion of the protein solvation water) is more proble matic for phalloidin-F-actin that for native F-actin. We conclude that phalloidin-F-actin is not a bona fide substitute for native F-actin i n the ''in vitro motility assay''. (C) 1995 Academic Press, Inc.