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Titolo:
Multiple transport pathways for dibasic amino acids in the larval midgut of the silkworm Bombyx mori
Autore:
Casartelli, M; Leonardi, MG; Fiandra, L; Parenti, P; Giordana, B;
Indirizzi:
Univ Milan, Dept Biol, I-20133 Milan, Italy Univ Milan Milan Italy I-20133 iv Milan, Dept Biol, I-20133 Milan, Italy Univ Milan, Dept Environm Sci, I-20126 Milan, Italy Univ Milan Milan Italy I-20126 , Dept Environm Sci, I-20126 Milan, Italy
Titolo Testata:
INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY
fascicolo: 6-7, volume: 31, anno: 2001,
pagine: 621 - 632
SICI:
0965-1748(20010427)31:6-7<621:MTPFDA>2.0.ZU;2-P
Fonte:
ISI
Lingua:
ENG
Soggetto:
BORDER MEMBRANE-VESICLES; MANDUCA-SEXTA MIDGUT; LEPIDOPTERAN LARVAE; PLASMA-MEMBRANE; K+/H+ ANTIPORT; PROTON PUMP; SYSTEMS; LEUCINE; PH; PHENYLALANINE;
Keywords:
arginine and lysine; transport pathways; BBMV; lepidopteran larval midgut; Bombyx mori;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Agriculture,Biology & Environmental Sciences
Life Sciences
Citazioni:
34
Recensione:
Indirizzi per estratti:
Indirizzo: Giordana, B Univ Milan, Dept Biol, Via Celoria 26, I-20133 Milan, Italy Univ Milan Via Celoria 26 Milan Italy I-20133 33 Milan, Italy
Citazione:
M. Casartelli et al., "Multiple transport pathways for dibasic amino acids in the larval midgut of the silkworm Bombyx mori", INSEC BIO M, 31(6-7), 2001, pp. 621-632

Abstract

The transport pathways for dibasic amino acids were investigated in brush border membrane vesicles (BBMV) from the anterior-middle (AM) and posterior(P) regions of Bombyx mori midgut. In the absence of K+, a low-affinity saturable transport of arginine in both AM- and P-BBMV (K-m 1.01 mM, V-max 4.07 nmol/7s/mg protein and K-m 1.38 mM, V-max 2.26 nmol/7s/mg protein, respectively) was detected. Arginine influx was dependent on the membrane electrical potential (Delta psi) and increased raising the alkalinity of the external medium from pH 7.2 to 10.6. Competition experiments indicated the following order of substrate affinity: arginine, homoarginine, N-G-monomethylarginine, N-G-nitroarginine > lysine much greater than omithine > cysteine > methionine, Leucine, valine and BCH (2-amino-2-norbornanecarboxylic acid) did not inhibit arginine influx. In the presence of external K+. the influx of arginine as a function of arginine concentration fitted to a complex saturation kinetics compatible with both a low-affinity and a high-affinity component. The latter (K-m 0.035 mM, V-max 2.54 nmol/7s/mg protein) was fullycharacterized. The influx rate had an optimum at pH 8.8, was strongly affected by Delta psi and was homogeneous along the midgut. The substrate affinity rank was: homoarginine > arginine, N-G-monomethylarginine much greater than cysteine, lysine much greater thanN(G)-nitroarginine > ornithine > methionine. Leucine and amino acids with a hydrophobic side chain were not accepted. This system is also operative in the absence of potassium, with the same order of specificity but a very low activity. Lysine influx is mediated by two more transport systems, the leucine uniport and the K+/leucine symport specific for amino acids with a hydrophobic side chain that recognizeslysine at extravesicular pH values (pH(out)) exceeding 9. Both the uniportand the symport differ from the cationic transport systems so far identified in mammals because they are unaffected by N-ethylmaleimide, have no significant affinity for neutral amino acids in the presence of the cation and show a striking difference in their optimum pH. (C) 2001 Elsevier Science Ltd. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 08/08/20 alle ore 08:13:36