We investigated the kinetics of leucine influx as a funtion 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-norbornanecarboxylic 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.

Evidence for a low-affinity, high-capacity uniport for amino acids in Bombyx mori larval midgut / M.G. Leonardi, M. Casartelli, P. Parenti, B. Giordana. - In: AMERICAN JOURNAL OF PHYSIOLOGY. REGULATORY, INTEGRATIVE AND COMPARATIVE PHYSIOLOGY. - ISSN 0363-6119. - 274:5(1998), pp. R1372-R1375.

Evidence for a low-affinity, high-capacity uniport for amino acids in Bombyx mori larval midgut

M.G. Leonardi;M. Casartelli;B. Giordana
1998

Abstract

We investigated the kinetics of leucine influx as a funtion 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-norbornanecarboxylic 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.
Neutral amino acid uniporter; Regional distribution; Specificity
Settore BIO/09 - Fisiologia
1998
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/193689
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