Characterization of the aminopeptidase from Bacillus subtilis as an extracellular enzyme

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Abstract
A strain of Bacillus subtilis produced an aminopeptidase detectable in the cultural fluid and in cell-free extracts. Both extracellular and intracellular aminopeptidases hydrolyzed L-leucyl-β-naphthylamide substrate after activation with cobalt ions. In the cultural fluid, trace amounts of activity were present as early as 12 h, but the highest activity was attained between 36 and 96 h. The addition of lysozyme to cultures less than 36 h old inhibited the production of the aminopeptidase of the cultural fluid, but was less effective in older cultures. This trend was correlated to the Gram-variability of the organisms in the culture. Chloramphenicol and oxytetracycline also inhibited enzyme production without affecting normal cell lysis. These data were interpreted to imply that the aminopeptidase of the cultural fluid did not result from the release of the intracellular aminopeptidase by cell lysis, but that it was produced by viable, metabolizing cells, most probably Gram-negative. Chromatography of the cultural fluid on CM-Sephadex C-50 showed an aminopeptidase characteristic of the extracellular medium. The possible implication of this enzyme as a regulatory mechanism for nitrogen utilization by Bacillus subtilis is discussed.

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