Mechanism of Excretion of a Bacterial Proteinase: Factors Controlling Accumulation of the Extracellular Proteinase of a Sarcina Strain (Coccus P)

Abstract

It has been known that the extracellular proteinase of Coccus P is found only in cultures grown in the presence of Ca 2+ . It is now shown that this cation is required neither for synthesis, excretion, or activation of a zymogen nor as a prosthetic factor necessary for enzymatic activity. The only function of Ca 2+ is to stabilize the active structure of the enzyme molecule, presumably by substituting for absence of S-S bridges. In the absence of Ca 2+ , the excreted proteinase undergoes rapid autodigestion and, instead of the active protein, its hydrolytic products are accumulated in the culture fluid. In minimal medium and under conditions of enzyme stability [presence of Ca 2+ and Ficoll (Pharmacia)], Coccus P accumulates the proteinase at a gradually reduced speed although the rate of cultural growth remains constant. It is shown that this decline in rate of accumulation is caused by the excreted proteinase itself, possibly acting on its own precursor emerging from the cell in a form susceptible to proteolytic attack and not amenable to Ca 2+ protection. A proteinase precursor is actually demonstrable in a calciumless culture at the onset of the enzyme accumulation which follows Ca 2+ addition. It is suggested that excreted proteins require an unfolded (or incompletely folded) structure to cross the cell envelope.