Changes in particulate-bound protease activity during cold acclimation in Tetrahymena pyriformis.

The protease activity, as assayed at pH 8.0 with azocasein as substrate, of a ciliate protozoan Tetrahymena pyriformis NT-1, was found to alter by growing the cells at various constant temperatures or at shifted temperatures. The intracellular protease activity, when cells were grown at either constant 39 degrees C or 15 degrees C, was decreased throughout the growth phase with significant secretion into the medium. On the other hand, when the culture temperature was transferred from 39 degrees C to 15 degrees C, the protease activity in cells was greatly increased up to about 28-fold at 8 h after the shift. There was, however, no secretion into the medium during the cold acclimation after the shift, where no cell division occurred. The elevated protease activity was quickly decreased to the control level when the culture was warmed to 39 degrees C after 8-h chilling, and recovery of normal cell division was seen. The marked increase in the protease activity caused by the shift to 15 degrees C was completely blocked by the addition of either cycloheximide or actinomycin D. The thermally induced enhancement of protease activity was found to occur with no different preference between three protease fractions.