[Free proteolytic activity from Serratia marcescens. II. Kinetics of production and mechanism of induction].

This paper shows that Serratia marcescens WF yields free proteolytic activity partially associated to growth, i.e. when the maximal rate of growth is reached, when it was growing in a saline medium supplemented with casein peptone. When the culture medium was utilized for a second time after it was used up (exhausted medium), growth and yield of free proteolytic activity showed the same partial association. With a protein medium containing peptides from 1000 to 5000 of molecular weight, from casein peptone, growth and yield of free proteolytic activity were partially associated too. In this paper, we demonstrated that Serratia marcescens WF yields free proteolytic activity only when growth rate is decelerating and under no growth conditions. We also demonstrated than the inducer structure acts gratuitously, because it cannot be used like a carbon and/or energy source. The structural form of the true inducer remains to be established. Finally, we propose that when growth rate is decelerating, or under no growth conditions, Serratia marcescens WF yields free proteolytic activity to obtain nitrogen from protein sources, apparently as the only function.