Charged casein-derived oligopeptides competitively inhibit the transport of a reporter oligopeptide by Lactococcus...

To study the effect of casein-derived peptides, accumulated during growth of Lactococcus lactis in milk, on its oligopeptide transport (Opp) function.

This effect was estimated by analysing the ability of casein-derived peptides to compete for the transport of a reporter peptide by whole L. lactis cells. The transport of the reported peptide was monitored by determining the intracellular concentrations of the corresponding amino acids by means of reverse-phase high-performance liquid chromatography (HPLC). Uptake of the reporter peptide was competitively inhibited by casein-derived peptides. The competition was only because of charged casein-derived peptides, including anionic peptides. The design of specific pure peptides made it possible to evidence for a positive (or negative) influence exerted by the positively (or negatively) charged side chain of the N-terminal amino acid on the competition.

Charged casein-derived peptides impaired the oligopeptide transport function of L. lactis.

These results demonstrate an inhibition of Opp when too many peptides are produced by the proteinase. Peptide transport by Opp therefore represents a bottleneck for increasing the growth rate of L. lactis in milk.