title: Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable.
abstract: At least 50% of the actin in resting human platelets is unpolymerized, and the bulk of this unpolymerized actin is complexed with a recently identified acidic, heat-stable 5-kDa peptide, named "Fx." Purified Fx binds stoichiometrically to muscle G-actin, forming a complex identifiable by nondenaturing polyacrylamide gel electrophoresis. Formation of the complex inhibits salt-induced polymerization of G-actin. Here we report that Fx is indistinguishable from thymosin beta 4, an acidic, heat-stable 5-kDa peptide first isolated from calf thymus and thought to be a thymic hormone. The complete amino acid sequence of Fx was determined and was found to be identical with that of thymosin beta 4. Authentic thymosin beta 4 is functionally equivalent to Fx, forming a 1:1 complex with actin monomers and inhibiting polymerization. The widespread distribution and high intracellular concentration of thymosin beta 4 (Fx) strongly suggest that it plays a significant role in regulating actin polymerization in many cell types.
authors.affiliation: Department of Anatomy, School of Medicine, University of Pennsylvania, Philadelphia 19104-6058.
authors.forename: D
authors.initials: D
authors.lastname: Safer
authors.forename: M
authors.initials: M
authors.lastname: Elzinga
authors.forename: V T
authors.initials: VT
authors.lastname: Nachmias
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000737:chemistry; D006801:Humans; D008840:Microfilament Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D013947:Thymosin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000099201:Thymosin beta(4)
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D010446:Peptide Fragments; D013947:Thymosin; D000099201:Thymosin beta(4)