Dipeptide transport by crustacean hepatopancreatic brush-border membrane vesicles

Abstract

Epithelial brush-border membrane vesicles (BBMVs) of lobster (Homarus americanus) hepatopancreas were formed by a Mg2+ precipitation technique. In these BBMVs, [14C]glycylsarcosine ([14C]Gly-Sar) uptake was stimulated by a transmembrane proton gradient. transmembrane K+ diffusion potential (inside negative) stimulated [14C]Gly-Sar uptake above that observed with short-circuited vesicles, while an inwardly directed Na+ gradient had no stimulatory effect on peptide uptake. [14C]Gly-Sar influx (over 10 s) occurred by a low-affinity, saturable, proton-gradient-dependent carrier system (Kt=5.90&plusmn;0.13 mmol l-1, Jmax=4662&plusmn;487 pmol mg-1 protein 10 s-1; mean &plusmn; s.e.m., N=3). This carrier exhibited a high-affinity proton binding site (KH=235&plusmn;25 nmol l-1; pK=6.6) and an apparent 1H+:1Gly-Sar transport stoichiometry. Influx of 0.1 mmol l-1 [14C]Gly-Sar into lobster hepatopancreatic BBMVs was significantly (P<0.01) cis-inhibited by 10 mmol l-1 diethylpyrocarbonate and by a variety of other dipeptides (10 mmol l-1), suggesting a broad transport specificity. These observations strongly suggest that transport of peptides into crustacean hepatopancreas is proton-gradient-dependent and electrogenic, qualitatively resembling the peptide transport paradigm proposed for fish and mammals.