pH-dependent heterogeneity of acidic amino acid transport in rabbit jejunal brush border membrane vesicles

• Published in: The Journal of biological chemistry Vol. 267; no. 3; pp. 1510 - 1516
• Main Authors: Maenz, D D, Chenu, C, Breton, S, Berteloot, A
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 25.01.1992; American Society for Biochemistry and Molecular Biology
• Subjects: amino acids; Amino Acids - pharmacology; Animals; Aspartic Acid - metabolism; Aspartic Acid - pharmacology; Biological and medical sciences; Biological Transport - drug effects; brush border membranes; Cell physiology; effects on; Fundamental and applied biological sciences. Psychology; Glutamates - metabolism; Glutamic Acid; Hydrogen-Ion Concentration; Intestinal Mucosa - metabolism; jejunum; Jejunum - metabolism; Kinetics; Membrane and intracellular transports; Microvilli - drug effects; Microvilli - metabolism; Molecular and cellular biology; Rabbits; transport; vesicles; Vertebrata; Regulation(control); Mammalia; Jejunum; Acids; Radiolabelling; Membrane transport; Aminoacid; Rabbit; pH; Lagomorpha
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)45975-3

Initial rates of Na(+)-dependent L-glutamic and D-aspartic acid uptake were determined at various substrate concentrations using a fast sampling, rapid filtration apparatus, and the resulting data were analyzed by nonlinear computer fitting to various transport models. At pH 6.0, L-glutamic acid transport was best accounted for by the presence of both high (Km = 61 microM) and low (Km = 7.0 mM) affinity pathways, whereas D-aspartic acid transport was restricted to a single high affinity route (Km = 80 microM). Excess D-aspartic acid and L-phenylalanine served to isolate L-glutamic acid flux through the remaining low and high affinity systems, respectively. Inhibition studies of other amino acids and analogs allowed us to identify the high affinity pathway as the X-AG system and the low affinity one as the intestinal NBB system. The pH dependences of the high and low affinity pathways of L-glutamic acid transport also allowed us to establish some relationship between the NBB and the more classical ASC system. Finally, these studies also revealed a heterotropic activation of the intestinal X-AG transport system by all neutral amino acids but glycine through an apparent activation of Vmax.