Actin polymerization as a mechanochemical reaction -its role in cell shape change

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Aim of the research : in order to elucidated the mechanism of cell locomotion, we have developed a system in which actin monomersare incorporated in liposomes and polymerized. We found that the liposomes deformed upon actin polymerization. We thus aimed to further investigate the change accompanying the actin polymerization in the liposomes.Plan : (1)to investigate if ATP hydrolysis is necessary for the liposome deformation. (2)to polymerize the actin in a liposome after making projections of phospholipid membrane with an electric field generated at the tip of a needle type electrode in order to sudy if the pre-formed projection is supported by polymerizing actin afterward by introducing ions into the liposome withthe addition of ionophore.Results : (1) this is still under investigation. the reason for this is beacuse it is extremely dificult to remove completely ATP from the system. Unless the complete removal is guaranteed, cnclusive result will be difficult to obtain. (2) introduction ofK ions into the actin containing liposome with the ionophore valinomycin was found to be successful : we found that rigid and spindle-shaped liposomes appeared when the actin-containingliposomes are added into solution containing K ions. However, pulling out the projections from the liposome was found to be difficult to reproduce. This was partly because the condition tobe achieved for successful membrane deformation requires subtle control of electrode shape, positioning, and electric field intensity. Further investigation is needed to optimize those conditions.