A study of the substrate specificity of Na+-dependent and Na+-independent neutral amino acid transport systems in dog intestinal brush-border membrane vesicles using L-alanine analogues.
Neutral amino acids are mainly transported across the intestinal brush-border membrane by two Na+-dependent systems (system B0 and system B0+) and one Na+-independent system (system b0,+). To investigate potential differences in substrate specificity between these systems, we screened ten different alanine analogues for their ability to inhibit the transport of L-alanine in dog intestinal brush-border membrane vesicles. The results suggested that a phenyl group directly attached to the alpha-carbon has different effects on the Na+-dependent and Na+-independent transport systems, with an increased affinity for the former and a decreased affinity for the latter. Based on these inhibition studies, we investigated [14C]L-phenylglycine transport kinetics in comparison with L-alanine. Similar to L-alanine, L-phenylglycine transport followed at least three routes, however, the Km of the Na+-dependent transport system was lower and the K'm of the Na+-independent system was higher than the corresponding values for L-alanine. These results corroborated the conclusions drawn from the inhibition studies. Based on these data, we conclude that different sizes of immediate parts to the alpha-carbon in functional groups of amino acid analogues have differential effects on the interaction of these amino acid analogues with the Na+-dependent and Na+-independent transport systems for neutral amino acids.
Hatanaka
Takahiro
T
Fuji Gotemba Research Laboratory, Chugai Pharmaceutical Co, Ltd, Shizuoka, Japan. hatanakatkh@chugai-pharm.co.jp
Nabuchi
Yoshiaki
Y
Ushio
Hidetoshi
H
D000409:Alanine / Q000031:analogs & derivatives / Q000737:chemistry / Q000493:pharmacokinetics*; D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002244:Carbon / Q000378:metabolism; D002250:Carbon Radioisotopes / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D010649:Phenylalanine / Q000737:chemistry / Q000493:pharmacokinetics; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012965:Sodium Chloride / Q000378:metabolism* / Q000494:pharmacology
D026921:Amino Acid Transport Systems, Neutral; D002250:Carbon Radioisotopes; D004791:Enzyme Inhibitors; D012965:Sodium Chloride; D010649:Phenylalanine; C008852:2-phenylglycine; D002244:Carbon; D000409:Alanine; D011188:Potassium; D005998:Glycine