摘要：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 EC50 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.
