Periplasmic aminopeptidases in Acinetobacter calcoaceticus and Pseudomonas aeruginosa

The greater part of the intracellular aminopeptidases in Pseudomonas aeruginosa and Acinetobacter calcoaceticus is soluble. The localization of aminopeptidases in the cells was examined using the osmotic shock method with some modifications. When the cells of A. calcoaceticus and P. aeruginosa of the logarithmic phase were subjected to an osmotic shock, all aminopeptidases investigated were mainly localized in the sucrose supernatants and in the periplasm. Acid phosphatase as marker enzyme for periplasm showed a similar distribution between the fractions as the aminopeptidases. The periplasmic aminopeptidases of both microorganisms were separated by FPLC on Superose 12 and their molecular masses were determined. The results obtained show that at least four different aminopeptidases occur in the periplasm, a leucyl aminopeptidase (LAP, cleaving Leu-NH-NH2, 400 kDa), a glutamyl aminopeptidase (GAP, 200 kDa), an alanyl aminopeptidase (AAP, 80 kDa) and a prolyl aminopeptidase (PAP, 65 kDa). The results are in agreement for both species. Our results show clearly that aminopeptidases of these typical members of Gram-negative bacteria are mainly periplasmic like degrading enzymes (alkaline and acid phosphatases, 5'-nucleotidase, cyclic phosphodiesterase), detoxifying enzymes and binding proteins for amino acids and sugars.