DIPEPTIDE TRANSPORT BY CRUSTACEAN HEPATOPANCREATIC BRUSH-BORDER MEMBRANE-VESICLES

Epithelial brush-border membrane vesicles (BBMVs) of lobster (Homarus americanus) hepatopancreas were formed by a Mg2+ precipitation techniq ue, In these BBMVs, [C-14]glycylsarcosine ([C-14]Gly-Sar) uptake was s timulated by a transmembrane proton gradient, transmembrane K+ diffusi on potential (inside negative) stimulated [C-14]Gly-Sar uptake above t hat observed with short-circuited vesicles, while an inwardly directed Na+ gradient had no stimulatory effect on peptide uptake. [C-14]Gly-S ar influx (over 10 s) occurred by a low-affinity, saturable, proton-gr adient-dependent carrier system (K-t=5.90+/-0.13 mmoll(-1), J(max)=466 2+/-487 pmol mg(-1) protein 10 s(-1); mean +/- S.E.M., N=3). This carr ier exhibited a high-affinity proton binding site (K-H=235+/-25 nmoll( -1); pK=6.6) and an apparent 1H(+):1Gly-Sar transport stoichiometry. I nflux of 0.1 mmoll(-1) [C-14]Gly-Sar into lobster hepatopancreatic BBM Vs was significantly (P<0.01) cis-inhibited by 10 mmoll(-1) diethylpyr ocarbonate and by a variety of other dipeptides (10 mmoll(-1)), sugges ting a broad transport specificity, These observations strongly sugges t that transport of peptides into crustacean hepatopancreas is proton- gradient-dependent and electrogenic, qualitatively resembling the pept ide transport paradigm proposed for fish and mammals.