title: Thymosin beta 4 (T beta 4) in activated platelets.
abstract: When resting human blood platelets are stimulated with thrombin, 50 to 60% of the G-actin polymerizes to F-actin within 60 seconds. The increase in F-actin is correlated with a corresponding decrease in the complex of G-actin with T beta 4. Within 5 seconds after stimulation, nucleation sites for pyrene actin polymerization increase 1.5 times in Triton-lysed supernatants. Cytochalasin D, known to inhibit the increase in F-actin after thrombin, also inhibits the fall in T beta 4-actin complex and the increase in nucleation sites. Phosphorylation of T beta 4 could not be detected in either control or activated cells. Increased T beta 4 corresponding to that lost from the T beta 4-actin complex is present in lysates from activated platelets and retains the ability to complex with actin. The data, taken together with previous estimates for the dissociation constant of the T beta 4-actin complex, show that actin polymerization following platelet activation could be controlled primarily by the increased availability of free barbed ends of actin filaments which have a higher affinity for G-actin than does T beta 4 and suggest that the increased free T beta 4 may serve to limit the degree of polymerization.
authors.affiliation: Department of Cell and Developmental Biology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6058.
authors.forename: V T
authors.initials: VT
authors.lastname: Nachmias
authors.forename: L
authors.initials: L
authors.lastname: Cassimeris
authors.forename: R
authors.initials: R
authors.lastname: Golla
authors.forename: D
authors.initials: D
authors.lastname: Safer
mesh_terms: D000199:Actins / Q000378:metabolism*; D001792:Blood Platelets / Q000737:chemistry* / Q000648:ultrastructure; D006801:Humans; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects; D011108:Polymers; D011499:Protein Processing, Post-Translational; D013917:Thrombin / Q000494:pharmacology; D013947:Thymosin / Q000032:analysis* / Q000378:metabolism; D000099201:Thymosin beta(4)
chemical_list: D000199:Actins; D011108:Polymers; D013917:Thrombin; D013947:Thymosin; D000099201:Thymosin beta(4)