THESE Maryse Bonnin Jusserand - Université de Bourgogne

Proteolysis of peptides
Résultats
Tyramine could be produced from peptides via two different ways. Peptides could be
hydrolyzed in the extracellular medium by peptidases or could be transported inside the cell
by peptide transporter. Inside the cells, peptides could be hydrolyzed by intracellular
peptidases, the released tyrosine could then be decarboxylated in tyramine which could be
released by the tdc permease. However, this last hypothesis is unlikely, since the tdc
transporter catalyses the exchange of tyrosine and tyramine. To verify that the peptides were
hydrolyzed in the extracellular medium, tyrosine in the extracellular medium was determined
during the growth of L. plantarum (Figure 3).
Figure 3: Tyrosine measured in the supernatants of the culture media containing synthetic
peptides. To: tyrosine measured in fresh media, before inoculation with L. plantarum IR
BL0076.
In the peptide medium, a high concentration in tyrosine is detected when cells are in the
exponential growth phase. Therefore synthetic peptides are hydrolyzed in the extracellular
medium, and tyrosine is mainly released at the beginning of the growth. So tyramine
measured is formed from peptides containing tyrosine hydrolyzed in the extracellular
medium. Regarding the proteolytic system, the sequenced strain L. plantarum WCFS1 has
uptake systems for peptides, like oligopeptide transport system Opp. Once internalized,
peptides can be degraded by peptidases Indeed, L. plantarum WCFS1 has nineteen genes
encoding intracellular peptidases of different specificity (Kleerebezem et al, 2003). But it has
been shown, for one isolate, that L. plantarum can harbor an extracellular proteinase PrtP
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