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Appl. Environ. Microbiol., Jan 1996, 156-161, Vol 62, No. 1
W Meijer, JD Marugg and J Hugenholtz
Two different Lactococcus lactis host strains, L. lactis subsp. lactis
MG1363 and L. lactis subsp. cremoris SK1128, both containing plasmid
pNZ521, which encodes the extracellular serine proteinase (PrtP) from
strain SK110, were used to study the medium and growth-rate-dependent
activity of three different enzymes involved in the proteolytic system of
lactococci. The activity levels of PrtP and both the intracellular
aminopeptidase PepN and the X-prolyl-dipeptidyl aminopeptidase PepXP were
studied during batch and continuous cultivation. In both strains, the PrtP
activity level was regulated by the peptide content of the medium. The
highest activity level was found during growth in milk, and the lowest
level was found during growth in the peptide-rich laboratory medium M17.
Regulation of the intracellular peptidase activity appeared to be a
strain-dependent phenomenon. In cells of strain MG1363, the activity levels
of PepN and PepXP were regulated in a similar way to that observed for
PrtP. In cells of strain SK1128, the levels of both peptidases were not
significantly influenced by the peptide content of the medium. The presence
of specific concentrations of the dipeptide prolylleucine could mimic the
low activity levels of the regulated proteolytic enzymes, even to the
activity level found on M17 medium. The effect of the presence of the
dipeptide prolylleucine in the medium on the activity level of the
regulated proteolytic enzymes was confirmed at fixed growth rates in
chemostat cultures.
Copyright © 1996, American Society for Microbiology
Regulation of Proteolytic Enzyme Activity in Lactococcus lactis
Departments of Microbiology and Biophysical Chemistry, National Institute for Dairy Research (NIZO), 6710 BA Ede, The Netherlands
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