Occurrence of Extracellular Acidic Endopeptidase of an Aerobic Spore-Forming Bacterium

Endopeptidases are produced by many aerobic spore-forming bacteria, such as Bacillus licheniforms (1), Bacillus mesentericus (2), and Bacillus subtilis (3–6, 8). The endopeptidases obtained from most of these sources have been purified and characterized. Among the various physico-chemical properties of these endopeptidases, their pH optimum for activity is of special interest. The pH optima of the enzymes from these sources are neutral or alkaline to about pH 10. The endopeptidases of such bacteria having pH optimum on the acidic side have not been reported. This preliminary report deals with the preparation and some properties of an acidic endopeptidase of bacteria designated as FR-2 (9), a variant of B. subtilis. The selection of this organism has added significance as Cheddar cheese prepared from the enzyme obtained from it was reported to be good and showed no bitter taste (9). Bacillus subtilis was grown on an milk agar slant for 24 hr at 37C.