CHARACTERIZATION OF THE PRINCIPAL INTRACELLULAR ENDOPEPTIDASE FROM LACTOCOCCUS-LACTIS SUBSP LACTIS MG1363

The major 70 kDa endopeptidase from the cytoplasm of plasmid-free Lactococcus lactis subsp. lactis MG1363 was purified to homogeneity. The enzyme was immunologically identical with the 70 kDa endopeptidase isolated by others from L. lactis subsp. cremoris Wg2. The enzyme did not hydrolyse alpha(sl)-, beta- or k-casein (CN) but it readily hydrolysed alpha(sl)-CN f1-23, alpha(sl)-CN f165-199 and three of five minor peptides released from alpha(sl)-CN by chymosin. The enzyme also hydrolysed a number of peptide hormones. It cleaved preferentially the peptide bonds of alpha(sl)-CN f1-23, alpha(sl)-CN f165-199, oxidized insulin chain B and synthetic peptides which contained hydrophobic amino acids at position P-1', including Pro-Leu bonds. The enzyme also hydrolysed the Gly-Phe bond of methionine enkephalin. Mole than 95% of enzyme activity was inhibited by 1 mM of o-phenanthroline or phosphoramidon. The enzyme was also inhibited strongly by a peptide fraction isolated from Cheddar cheese.