AMINOPEPTIDASE-N FROM STREPTOCOCCUS-SALIVARIUS SUBSP THERMOPHILUS NCDO-573 - PURIFICATION AND PROPERTIES

A 96 kDa aminopeptidase was purified from Streptococcus salivarius sub sp. thermophilus NCDO 573. The enzyme had similar properties to aminop eptidases isolated from lactococci and lactobacilli and showed a high degree of N-terminal amino acid sequence homology to aminopeptidase N from Lactococcus lactis subsp. cremoris. It catalysed the hydrolysis o f a range of aminoacyl 4-nitroanilides and 7-amido-4-methylcoumarin de rivatives, dipeptides, tripeptides and oligopeptides. In common with a minopeptidases from other lactic acid bacteria, the enzyme from Strep. salivarius subsp. thermophilus showed highest activity with lysyl der ivatives but was also very active with arginyl and leucyl derivatives. Relative activity with alanyl, phenylalanyl, tyrosyl, seryl and valyl derivatives was considerably lower and with glycyl, glutamyl and prol yl derivatives almost negligible. The aminopeptidase also catalysed th e hydrolysis of dipeptides and tripeptides but mostly at rates much le ss than that with L-lysyl-4-nitroanilide and oligopeptides. The enzyme catalysed the successive hydrolysis of various amino acid residues fr om the N-termius of several oligopeptides but it was unable to cleave peptide bonds on the N-terminal side of a proline residue.