OCCURRENCE OF AMINO ACID NAPHTHYLAMIDASE DISTINCT FROM LEUCINE AMINOPEPTIDASE IN SERRATIA INDICA

An enzyme which hydrolyzes amino acid naphthylamides, an arylamidase, was found in cell extracts of S. indica. The cells also contain a leucine aminopeptidase. The latter enzyme is distinct from the arylamidase, which is without activity against L-leucine amide. A separate esterase hydrolyzing B-naphthylacetate was demonstrated in the extract. The arylamidase activity is highest during the late exponential phase of cultures grown in complex peptone media, but the enzyme is also produced by cells grown in a synthetic salt medium containing glycerol. The optimal pH for the hydrolysis of L-leucyl-B-naphthyl-amide is between 6 and 7. The enzyme requires divalent metal ions and is not very stable. Attempts to purify the enzyme were hindered by activity losses. The inadequacy of chromogenic naphthylamides as substrates for the assay of peptidase activity of bacteria is discussed.