Peptide Hydrolases of Lactobacillus helveticus and Lactobacillus delbrueckii ssp. bulgaricus

Lactobacillus helveticus C M U 32 had more aminopeptidase and dipeptidase activity than did Lactobacillus helveticus ATCC 10797 or Lactobacillus delbrueckii ssp.bulgaricus ATCC 12278, whereas L. helveticus ATCC 10797 was most proteolytic (loo%), followed closely by L. helveticus CNRZ 32 (92%), and L. delbrueckii ssp.bulgaricus ATCC 12278 (50%).Crude cell-free extracts of the three lactobacilli lacked carboxypeptidase and endopeptidase activities.Lactobacillus helveficus (JNRZ 32 had two aminopeptidase-active bands, whereas L. helveticus ATCC 10797 and L. delbrueckii ssp.bulgaricus ATCC 12278 each had only one active aminopeptidase ban& relative mobility values of bands differed among strains.The three lactobacilli each had two active dipeptidase bands with different relative mobilities.Intracellular protease, aminopeptidase, and dipeptidase activities of L. helveticus CNRZ 32 i n m e d gradually at the beginning of the log phase and reached a maximum at the beginning of the stationary phase, but after 24 h, enzyme activity was slightly reduced.Freezing cells at -96'C and holding them at that temperature for 1 wk reduced aminopeptidase and dipeptidase activities 10% compared with those of unfrozen cells.The fbezing process also reduced the population of viable cells grown in MRS broth or skim milk by 50 or 75%, respectively.Aminopeptidase activity of cells grown in sterile skim milk or a whey-based medium did ~~