Abstract
Derepressed cells of Saccharomyces mellis were treated in one of several different ways to either elute or inactivate the exocellular enzyme, acid phosphatase. The enzyme was either (i) eluted from resting cells with 0.5 m KCl plus 0.1% beta-mercaptoethanol, (ii) eluted from exponential phase cells by growing the organism in derepressing media containing 0.5 m KCl, or (iii) inactivated on exponential phase cells by adding sufficient acid or base to growth media to destroy the enzyme but not enough to kill the cells. These treatments did not affect viability. Treated cells were transferred to fresh growth media or some other reaction mixture, and the kinetics of recovery of acid phosphatase activity was studied. In these reaction mixtures, enzyme was synthesized only by actively growing cells. Treated resting cells were indistinguishable from untreated, repressed resting cells in that the organism inoculated into complete growth medium remained in the lag phase for approximately 6 hr before both growth and enzyme synthesis began. Exponential phase derepressed cells treated by method (ii) or (iii) were transferred to fresh medium under conditions that allowed growth to continue. The cells immediately started to manufacture enzyme at a rate greater than normal until the steady-state level was reached, thus demonstrating a feedback control system. Exponential phase repressed cells were also transferred to fresh derepressing media under conditions which sustained growth. Though these cells began to grow immediately, there was a lag before acid phosphatase synthesis began followed by a lengthy inductive period. The length of the period of induction could be correlated with the polyphosphate content of the cells. As the supply of polyphosphate neared exhaustion, the rate of synthesis increased rapidly until it was greater than normal; this differential rate was sustained until the steady-state concentration was reached. When derepressed cells grow in a medium containing 0.5 m KCl, some acid phosphatase activity is found free in the culture fluid and some remains firmly attached to the cells despite the presence of the salt. The bound activity is subject to feedback control, but the steady-state level of this activity on the cells is only one-third that of the acid phosphatase on cells growing in nonsaline media. The extracellular phosphatase is produced at a rate that is several-fold greater than that of the exocellular enzyme in a nonsaline medium. The synthesis of the extracellular enzyme does not seem to be controlled by a feedback mechanism but is produced at a maximal rate as long as the cells are growing.