[Proteases in different membrane fractions of Acinetobacter calcoaceticus]

Distinct protease activities were found in membrane fractions from Acinetobacter calcoaceticus grown on acetate-NH4+ medium until early stationary phase. Mechanical or enzymatic cell disintegration followed by membrane fractionation through sucrose gradient revealed higher activities in the outer membrane than in the cytoplasmic membrane. Using azocasein and synthetic p-nitroanilides as substrates we found very low proteinase activities in intracytoplasmic membrane fractions. However, these fractions contained a significant aminopeptidase activity which was absent from cell envelope membranes. Peptidolytic activities in intracytoplasmic membranes of gram-negative bacteria have not been described before.