Maturation factor for the activation process of an extracellular proteinase in Lactobacillus helveticus CP790

A maturation factor that was needed for activation of an extracellular proteinase was partially purified from Lactobacillus helveticus CP790 by DEAE-Sepharose column chromatography, followed by gel filtration using HPLC. The protein had the ability to accelerate the conversion of proproteinase to active enzyme but had no proteolytic activity toward casein that had been treated with fluorescein isothiocyanate. The proteinase activities in the proproteinase fraction and the maturation protein fraction were not affected by preincubation of either fraction separately. However, when the mixture of the proproteinase and the maturation protein was incubated, the conversion of the proproteinase to active enzyme was accelerated, and proteinase activity increased. The production of some proteins that were specific to the active fractions was highest at the midlog phase of cell growth, which corresponded to the period of maximum proteinase activity. The results suggest that the proproteinase is activated to the mature enzyme not by an autocatalytic process but by the help of a maturation protein.