Functional expression of the oligopeptide transporter PepT1 from the sea bass (Dicentrarchus labrax).

Complementary RNA, derived from the intestine
of the sea bass Dicentrarchus labrax and putatively coding
for a pH-dependent oligopeptide transporter PepT1 (SLC15
family), was injected in Xenopus oocytes that were
subsequently tested with electrophysiological techniques.
Transport-associated currents were observed when various
di- or tripeptides were applied at concentrations ranging
between 0.1 and 10 mM. No currents were generated by
histidine nor by other single amino acids. Sea bass PepT1
also exhibited presteady-state currents in the absence of
substrates. Acidic pH slowed down the relaxation time
constant of these currents and shifted both Q/V and τ/V
relationships toward more positive voltages. Michaelis–
Menten analysis of the transport currents showed an
increase in apparent substrate affinity at acidic pH, which
was very similar to that exhibited by the related transporter
from zebrafish (Danio rerio), but in contrast, did not
demonstrate a significant effect of pH on the maximal
transport current.