Neutral amino acid transport by marine fish intestine: role of the side chain

Abstract

Abstract. This work was devoted to the study of the structure-affinity relationships in neutral amino acid transport by intestinal brush border of marine fish (Dicentrarchus labrax). The effects of the length of the side chain on kinetics of glycine, alanine, methionine and amino isobutyric acid were investigated. In the presence of K + two components were characterized: one is saturable by increased substrate concentrations, whereas the other can be described by simple diffusion mechanism. Simple diffusion, a passive, non-saturable, Na+-independent route, contributes largely to the transport of methionine and to a much lesser extend to alanine, glycine or alphaaminoisobutyric acid uptakes. If a branched chain is present, as in the case of amino isobutyric acid, diffusion is low. A Na+-independent, saturable system has been fully characterized for methionine, but not for branched amino acids such as amino isobutyric acid. In the presence of Na + saturable components were shown. Two distinct Na+-dependent pathways have been characterized for glycine uptake, with low and high aff• For alanine and methionine only one Na+-dependent high affinity system exists with the same half-saturation concentration and the same maximum uptake at saturable concentrations. Glycine high affinity system has the same half-saturation concentration as methionine or alanine uptake, whereas maximum uptake is lower. The substitution of the hydrogen by a methyl group results in a severe decrease of uptake (aminoisobutyric acid). Mutual inhibition experiments indicate that the same carriers could be responsible for methionine and alanine uptakes and probably glycine Na+-dependent uptake. The influence of Na + concentrations (100 -1 mol.1-1) on amino Abbreviations: [AA], amino acid concentration; AIB, aminoisobutyric acid; [/], Inhibitor amino acid concentration; Ji, uptake in the presence of inhibitor; Jo, uptake without inhibitor; K d, passive diffusion constant; K i, inhibitor constant; K t, concentration of test amino acid for half-maximal flux; MES, 2[N-morpholino]ethanesulphonic acid; Vma x, maximum uptake at saturable amino acid concentrations; Vto~, total amino acid uptake Correspondence to: G. Bog6 acid uptake was examined. Glycine, alanine, methionine and amino isobutyric acid transport can be described by a hyperbolic function, with a saturation uptake which is highly increased for methionine. However, the half-saturation concentration does not seem to be strongly affected by the amino acid structure. The effect of Na + concentration (25 and 100 mmol.1-1) on the kinetics of methionine uptake have been also examined. The maximum uptake of the saturable system clearly shows a typical relationship with concentration.

SLC transporters ASCT2, B0AT1‐like, y+LAT1, and LAT4‐like associate with methionine electrogenic and radio‐isotope flux kinetics in rainbow trout intestine

“…Flux measurement without Na + could not be mathematically modeled using both linear and nonlinear regression. This reinforces the role of sodium in regulating AAs absorption of teleost species (Balocco et al ; Ingham and Arme ; Lucia et al ; Maffia et al ; Mepham and Smith ; Miller and Kinter, ; Smith ; Vilella et al ).…”

“…Compared to mammals, considerably less information is available on the nutrient absorptive mechanisms in aquatic species. First studies on AAs absorption in fish include goldfish Carassius auratus (Mepham and Smith ), white grunt Haemulon plumieri (Smith ), rainbow trout Salmo gairdneri (Ingham and Arme ), killifish Fundulus heteroclitus (Miller and Kinter ), European yellow eel Anguilla anguilla (Maffia et al ), and sea bass Dicentrarchus labrax (Balocco et al ). Most of these studies have demonstrated that the Na + electrochemical gradient is the driving force for the absorption of AAs.…”

Trypsin and chymotrypsin as indicators of nutritional status of post‐weaned sea bass larvae

“…This hypothesis could be supported by data obtained by Boehlert & Yoklavich (1984) in Pacific herring Clupea Pallasi pallasi Valenciennes larvae, who found evidences that prolonged feeding periods and high rations decrease digestive efficiency as they increase evacuation rate. In addition, the absorption through the intestinal transporters of peptides and free amino acid can be saturated by high concentrations of these substrates (Balocco et al , 1993; Maffia et al , 1997; Verri et al , 2000).…”

Adaptations toin situfeeding: novel nutrient acquisition pathways in an ancient vertebrate

“…system Gly for glycine, system B 0 for L-alanine). Evidence also exists for both shared and distinct pathways for L-alanine and glycine absorption in the gut of teleost fish [14].…”