Biochemical characterization of the proteins of Paramecium secretory granules.

The proteins of trichocysts (secretory granules) from Paramecium tetraurelia have been biochemically characterized. Two-dimensional electrophoresis revealed 34 major components and at least 120 minor components, most with molecular weights ranging from 14,000 to 21,000 and isoelectric points ranging from 4.8 to 5.2. Comparison of two-dimensional electrophoretic patterns of trichocysts before and after exocytosis revealed only minor changes in these patterns, although the protein matrix undergoes a striking change in morphology. To clarify the interrelationships among trichocyst proteins, two proteins from extruded trichocyst matrix were purified to homogeneity and sequenced at their N termini. Their sequences are distinct, but they share limited homology.