title: The subcellular distribution of [3H]-colchicine-binding activity and tubulin in pig blood platelets.
abstract: The subcellular distribution of the [3H]-colchicine-binding protein, believed to be tubulin, the subunit protein of microtubules, has been investigated in mammalian blood platelets. Studies on a soluble extract from pig platelets and two particulate fractions (viz. membrane-rich and granule-rich fractions) have shown that about 98% of the colchicine-binding activity in a platelet homogenate is located in the soluble phase. This result is in agreement with polyacrylamide gel electrophoresis experiments which show that the soluble fraction contains a substantial amount of 55,000 MW tubulin, whereas the membrane and granule-rich fractions contain very little of this component. The [3H]-colchicine-binding activity of the platelet soluble phase is largely precipitated by 40-50% ammonium sulphate and also by vinblastine sulphate in millimolar concentrations. Moreover the colchicine-binding protein in the platelet soluble fraction has a sedimentation coefficient of 5.9 S, is eluted in the void volume of a Sephadex G-100 column, and binds to DEAE-Sephadex at low ionic strength and is eluted from this ion-exchanger at an ionic strength of 0.47 M-KCl. In addition, most of the colchicine-binding activity of the platelet soluble phase is associated with protein which will undergo temperature-dependent polymerization in vitro and which has a molecular weight on SDS-polyacrylamide gels of 55,000. All these experimental findings suggest that the colchicine-binding activity of pig platelet homogenates is due to the presence of the microtubule protein, tubulin, which is largely found in the soluble compartment of the cells.
mesh_terms: D000199:Actins / Q000302:isolation & purification; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D002458:Cell Fractionation; D003078:Colchicine / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D012701:Serotonin / Q000032:analysis; D013552:Swine; D014404:Tubulin / Q000378:metabolism*
chemical_list: D000199:Actins; D006023:Glycoproteins; D014404:Tubulin; D012701:Serotonin; D002374:Catalase; D010727:Phosphoric Diester Hydrolases; D003078:Colchicine