3H-L-leucine transport by the promiscuous crustacean dipeptide-like cotransporter

• Published in: Journal of experimental zoology. Part A, Ecological genetics and physiology Ecological genetics and physiology, 2011-10, Vol.315A (8), p.465-475
• Main Authors: Obi, I., Wells, A.L., Ortega, P., Patel, D., Farah, L., Zanotto, F.P., Ahearn, G.A.
• Format: Article
• Language: English
• Subjects: Amino Acid Transport Systems - metabolism; Animals; Cations - metabolism; Cytosol - metabolism; Dipeptides - metabolism; Hepatopancreas - metabolism; Homarus americanus; Intestines - metabolism; Kinetics; Leucine - metabolism; Male; Marine; Membranes - metabolism; Nephropidae - metabolism; Tritium; Zinc - metabolism
• ISSN: 1932-5223; 1932-5231; 1932-5231
• DOI: 10.1002/jez.694

The crustacean intestine and hepatopancreas display a variety of solute transport mechanisms for transmembrane transfer of dietary contents from lumen to epithelial cytosol. An in vitro intestinal perfusion apparatus was used to characterize mucosal to serosoal (MS) and serosal to mucosal (SM) Zn2+‐dependent 3H‐L‐leucine transport by the intestine of the American lobster, Homarus americanus. Transmural 20 µM MS 3H‐L‐leucine fluxes across lobster intestine were a hyperbolic function of luminal zinc concentration (1–50 µM) following Michaelis–Menten kinetics (Km = 2.67 ± 0.74 µM; Jmax = 19.56 ± 2.22 pmol/cm2×min). Transmural 20 µM SM 3H‐L‐leucine fluxes were not affected by serosal zinc, resulting in a highly significant stimulation of net amino acid transfer to the blood by luminal metal. MS fluxes of 20 µM 3H‐L‐leucine were also hyperbolic functions of luminal [Cu2+], [Mn2+], [Na+], and [H+]. MS flux of 3H‐L‐leucine was a sigmoidal function of luminal [L‐leucine] and was stimulated by the addition of 20 µM luminal zinc at both pH 7.0 and 5.5. A greater enhanced amino acid transport occurred at the lower pH 5.5. MS flux of 20 µM 3H‐L‐leucine in the presence of 20 µM zinc was significantly inhibited by addition of 100 µM luminal glycylsarcosine, and MS flux of 20 µM 3H‐glycylsarcosine was inhibited by 100 µM L‐leucine in the presence of 20 µM zinc. Results suggest that 3H‐L‐leucine and metals form a complex (e.g., Leu–Zn–Leu] that may functionally mimic dipeptides and use a dipeptide‐like transporter during MS fluxes as suggested for fish and mammals. J. Exp. Zool. 315:465–475, 2011. © 2011 Wiley‐Liss, Inc.