Nachmias V T, Cassimeris L, Golla R, Safer D
Department of Cell and Developmental Biology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6058.
Eur J Cell Biol. 1993 Aug;61(2):314-20.
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.
当用凝血酶刺激处于静息状态的人体血小板时，50%至60%的G-肌动蛋白会在60秒内聚合成F-肌动蛋白。F-肌动蛋白的增加与G-肌动蛋白与Tβ4复合物的相应减少相关。刺激后5秒内，芘肌动蛋白聚合的成核位点在经曲拉通裂解的上清液中增加1.5倍。细胞松弛素D已知可抑制凝血酶刺激后F-肌动蛋白的增加，它也抑制Tβ4-肌动蛋白复合物的减少和成核位点的增加。在对照细胞或活化细胞中均未检测到Tβ4的磷酸化。与从Tβ4-肌动蛋白复合物中丢失的Tβ4相对应增加的Tβ4存在于活化血小板的裂解物中，并保留了与肌动蛋白结合的能力。这些数据与之前对Tβ4-肌动蛋白复合物解离常数的估计相结合，表明血小板活化后的肌动蛋白聚合可能主要受肌动蛋白丝自由尖端可用性增加的控制，这些自由尖端对G-肌动蛋白的亲和力高于Tβ4，并表明游离Tβ4的增加可能有助于限制聚合程度。
