title: Evidence for a low-affinity, high-capacity uniport for amino acids in Bombyx mori larval midgut.
abstract: We investigated the kinetics of leucine influx as a function of external substrate concentration between 0.03 and 16 mM in brush-border membrane vesicles (BBMV) prepared from the middle region of Bombyx mori larval midgut. A detailed kinetic analysis of leucine uptake led to the identification, in parallel with the K(+)-dependent symporter for neutral amino acids, of a K(+)-independent, low-affinity, high-capacity system. The parameter values of the Michaelis constant (7.12 mM) and maximal rate of transport (4.48 nmol.7 s-1.mg protein-1) were not influenced by an external alkaline pH nor by a transmembrane electrical potential difference. The uniporter is poorly specific, as it displayed the following rank of preference: Leu, His, Val, Ile, Phe, Ser > Lys, Arg, Gln > Pro, 2-amino-2-norbornane-carboxylic acid, Ala, Gly. The kinetic analysis performed in BBMV prepared from the posterior midgut portion indicates that the low-affinity, high-capacity uniporter is present along the entire length of the silkworm larval midgut with similar expression and functional properties.
authors.affiliation: Department of Biology, University of Milan, Italy.
authors.forename: M G
authors.initials: MG
authors.lastname: Leonardi
authors.forename: M
authors.initials: M
authors.lastname: Casartelli
authors.forename: P
authors.initials: P
authors.lastname: Parenti
authors.forename: B
authors.initials: B
authors.lastname: Giordana
mesh_terms: D000596:Amino Acids / Q000502:physiology*; D000818:Animals; D012831:Bombyx; D017136:Ion Transport / Q000502:physiology; D007700:Kinetics
chemical_list: D000596:Amino Acids