Amino acid transport in plasma-membrane vesicles from rat liver. Characterization of L-alanine transport.
Plasma-membrane vesicles, isolated from rat liver, catalyze active transport of L-alanine. The transient accumulation of L-alanine requires the presence of Na+ concentration gradient (outside greater than inside). The alanine-Na+ symport is an electrogenic process, since it is stimulated under conditions that allow compensatory ion movements: both co-transported anions as well as counter-transported cations influence the rate of alanine-Na+ symport. However, no uptake is observed in the presence of a membrane potential, when no Na+ concentration gradient is present. Sodium-gradient-stimulated alanine uptake is dependent on temperature and pH, stereospecific, and is affected by the presence of other amino acids. The activity of the L-alanine transport system is influenced both by the Na+ and by the L-alanine concentration. In the presence of 100 mM Na+, an apparent Km for alanine of 2 mM is observed; lowering the Na+ concentration results in an increase in the apparent Km, and a decrease in the apparent V. The apparent Km for Na+ is 34 mM in the presence of 0.2 mM L-alanine. Increasing the L-alanine concentration also results in a lower apparent Km for Na+, and a higher V.
D000409:Alanine / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008564:Membrane Potentials; D051381:Rats; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D012964:Sodium; D000409:Alanine