A novel 60-kDa smooth muscle protein that binds filamin-actin filament complex

From the low salt-extracted debris of bovine stomach smooth muscle, a protein having a molecular mass of 60 kDa in SDS-PAGE was newly isolated. Co-sedimentation assay with actin filaments and several actin binding proteins such as filamin, alpha-actinin, caldesmon and fodrin showed that this protein co-sediments with actin only in the presence of filamin. Falling ball viscometric assay showed that this protein increases the viscosity of actin-filamin solution in a dose-dependent manner. Immunoblotting analysis showed specific localization of this protein in smooth and striated muscles.