The oligopeptide transporter PEPT1 (
SLC15A1) is responsible for absorption of peptidic nutrients in the small intestine. Although the
L-diastereomer of the β-lactam antibiotic cephalexin (
L-cephalexin) is likely to be transported by PEPT1, there has been no direct demonstration of PEPT1-mediated
L-cephalexin transport. Indeed, after the incubation with
L-cephalexin, the intact form of
L-cephalexin has not been identified inside vesicles/proteoliposomes prepared from brush border membrane of intestinal epithelial cells or cultured cell lines exogenously transfected with PEPT1 gene. Thus, it appears that
L-cephalexin is rapidly metabolized by PEPT1 or PEPT1-associated proteins. Here, we attempted to verify whether
L-cephalexin is transported by PEPT1 and whether it is hydrolyzed by PEPT1 itself, by using budded baculovirus expressing PEPT1 protein. Marked uptake of
L-cephalexin in PEPT1-expressing budded baculovirus, compared with wild-type virus, indicated that
L-cephalexin is a substrate for PEPT1. The uptake was found to be pH sensitive, and was strongly inhibited by the
D-diastereomer of cephalexin and glycylsarcosine, but not by glycine. Thus,
L-cephalexin is transported by PEPT1 itself. Upon the transport of both
L- and
D-cephalexin by PEPT1, dose-dependent membrane depolarization was observed; the EC
50 values of 0.18 and 2.9 m
M, respectively, indicate that the affinity of
L-cephalexin for PEPT1-mediated transport is much higher than that of the
D-diastereomer. On the other hand, the
L-cephalexin metabolite 7-aminodesacetoxycephalosporanic acid was not detected in PEPT1-expressing or wild-type virus at either pH 6.0 or 7.4. We conclude that
L-cephalexin is transported by PEPT1 with high affinity, but is not metabolized by PEPT1 itself.
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