The oral apparatus of Tetrahymena pyriformis, strain WH-6. III. The binding of 3H-cytochalasin B by the isolated oral apparatus.

The binding of tritium-labelled cytochalasin B by the isolated oral apparatus of Tetrahymena pyriformis, strain WH-6, syngen 1, was investigated. Equilibrium binding studies revealed approximately 1.4 x 10(5) cytochalasin B binding sites per oral apparatus. A Scatchard plot indicates a single class of binding affinities with an association constant of 10(5) liters/mole. Rapid release of oral apparatus-bound cytochalasin B occurred when oral apparatuses were washed and resuspended in 1 mM TRIS without cytochalasin B. Because cytochalasin B binding to oral apparatus microtubular protein was not detected, microtubules are probably not the cytochalasin B binding site. The probable nature of the cytochalasin B binding site within the oral apparatus is discussed.