Regulation of L-methionine and L-lysine uptake in chicken jejunal brush-border membrane by dietary methionine.
In the chicken intestine, L-methionine is transported by systems that are specific for neutral amino acids (L- and B-like) and by systems that can also transport cationic amino acids (y(+)m and b(0,+)-like). These four uptake pathways have been investigated in brush-border membrane vesicles from the jejunum of chickens fed a diet enriched with 0.4% L-methionine. Methionine supplementation from the 1st to the 6th wk of age has no effect on body weight or on the efficiency of food utilization. The kinetic analysis of L-methionine influx across the transport systems specific for neutral amino acids shows, for system L, no dietary effect on the Michaelis constant (Km) and a 30% reduction in maximal velocity (Vmax); for system B it shows a decrease in Km (30%) and in Vmax (51%). Transport systems shared by cationic and neutral amino acids show no dietary effect on b(0,+) activity and a significant reduction in y(+)m Vmax, similar for L-methionine and L-lysine, both in the absence and in the presence of Na+ (L-methionine, 30 and 26% reduction; L-lysine, 19 and 28% reduction, respectively). The downregulation induced by L-methionine supplementation may be an adaptive response to reduce the risk of intoxication by dietary excess of L-methionine. These results support the view that the toxicity of the supplemented substrate can be an important factor in the regulation of amino acid transport by dietary content.
Soriano-García
J F
JF
Departament de Fisiologia-Divisió IV, Facultat de Farmàcia, Universitat de Barcelona, 08028 Barcelona, Spain.
Torras-Llort
M
M
Moretó
M
M
Ferrer
R
R
D000284:Administration, Oral; D000596:Amino Acids / Q000494:pharmacology; D000598:Amino Acids, Cyclic; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002645:Chickens; D003553:Cystine / Q000494:pharmacology; D019587:Dietary Supplements; D005033:Ethylmaleimide / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000502:physiology*; D007583:Jejunum / Q000502:physiology*; D007700:Kinetics; D008239:Lysine / Q000378:metabolism*; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000378:metabolism*; D008871:Microvilli / Q000502:physiology*; D008954:Models, Biological; D008956:Models, Chemical; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D000598:Amino Acids, Cyclic; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D003553:Cystine; D012964:Sodium; D008715:Methionine; D008239:Lysine; D005033:Ethylmaleimide