title: Uptake of lysine and proline via separate alpha-neutral amino acid transport pathways in Mytilus gill brush border membranes.
abstract: Brush border membrane vesicles (BBMV) were prepared from the gills of the marine mussel, Mytilus edulis. These membranes contained two distinct pathways for cotransport of Na+ and alpha-neutral amino acids. The major pathway in mussel gill BBMV was the alanine-lysine (AK) pathway, which had a high affinity for alanine and for the cationic amino acid, lysine. The AK pathway was inhibited by nonpolar alpha-neutral amino acids and cationic amino acids, but was not affected by beta-neutral amino acids or imino acids. The kinetics of lysine transport were consistent with a single saturable process, with a Jmax of 550 pmol/mg-min and a Kt of 5 microM. The AK pathway did not have a strict requirement for Na+, and concentrative transport of lysine was seen in the presence of inwardly directed gradients of Li+ and K+, as well as Na+. Harmaline inhibited the transport of lysine in solutions containing either Na+ or K+. The alanine-proline (AP) pathway transported both alanine and proline in mussel gill BBMV. The AP pathway was strongly inhibited by nonpolar alpha-neutral amino acids, proline, and alpha-(methylamino)isobutyric acid (Me-AIB). The kinetics of proline transport were described by a single saturable process, with a Jmax of 180 pmol/mg-min and Kt of 4 microM. In contrast to the AK pathway, the AP pathway appeared to have a strict requirement for Na+. Na+-activation experiments with lysine and proline revealed sigmoid kinetics, indicating that multiple Na+ ions are involved in the transport of these substrates. The transport of both lysine and proline was affected by membrane potential in a manner consistent with electrogenic transport.
authors.affiliation: Department of Physiology, College of Medicine, University of Arizona, Tucson 85724.
authors.forename: A M
authors.initials: AM
authors.lastname: Pajor
authors.forename: S H
authors.initials: SH
authors.lastname: Wright
mesh_terms: D000409:Alanine / Q000493:pharmacokinetics / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D049872:Bivalvia / Q000378:metabolism*; D002414:Cations, Monovalent; D005880:Gills / Q000378:metabolism; D006246:Harmaline / Q000494:pharmacology; D007700:Kinetics; D008239:Lysine / Q000493:pharmacokinetics* / Q000494:pharmacology; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D011392:Proline / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D002414:Cations, Monovalent; D011392:Proline; D006246:Harmaline; D008239:Lysine; D000409:Alanine