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  • Title: Basolateral dipeptide transport by the intestine of the teleost Oreochromis mossambicus.
    Author: Thamotharan M, Zonno V, Storelli C, Ahearn GA.
    Journal: Am J Physiol; 1996 May; 270(5 Pt 2):R948-54. PubMed ID: 8928925.
    Abstract:
    Transport characteristics of [14C]glycylsarcosine ([14C]Gly-Sar) were measured in herbivorous tilapi (Oreochromis mossambicus) intestinal basolateral membrane vesicles (BLMV) purified with Percoll gradient centrifugation. Specific activity of the vesicle Na(+)-K(+)-adenosinetriphos- phatase was increased 12-fold, whereas specific activity of the brush-border enzyme alkaline phosphatase was enriched only by 0.8-fold. [14C]Gly-Sar uptake was stimulated by increasing concentrations of extravesicular protons rather than by a transmembrane proton gradient. A transmembrane K+ diffusion potential (inside negative) did not stimulate [14C]Gly-Sar uptake above that observed with short-circuited vesicles. An inwardly directed Na+ gradient had no effect on peptide uptake. Kinetic analysis of basolateral transport rate revealed that the transport occurred by a saturable process conforming to Michaelis-Menten kinetics [Kt [concentration of [14C]Gly-Sar that yielded one-half of maximal influx (Jmax)] = 13.27 +/- 3.80 mM, Jmax = 15,155 +/- 3,096 pmol.mg protein-1.6 s-1]. The basolateral transporter was insensitive to diethylpyrocarbonate (DEP), a specific inhibitor of proton-coupled peptide transport systems. [14C]Gly-Sar influx into tilapia BLMV showed cis-inhibition by several other dipeptides, suggesting that the [14C]Gly-Sar transporter was shared by other peptides too. These observations strongly suggest that the basolateral intestinal dipeptide transporter in herbivorous fishes is distinctly different from either the high- or low-affinity brush-border transporter. It is proton dependent, electroneutral, sodium independent and accepts a wide variety of dipeptides.
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