title: A comparison of the rate equations, kinetic parameters, and activation energies for the initial uptake of L-lysine, L-valine, gamma-aminobutyric acid, and alpha-aminoisobutyric acid by mouse brain slices.
abstract: At substrate concentrations, in medium, of 0.2 to 20 mM and at temperatures of 25 and 37 degrees C, the initial concentrative influx of the amino acids L-lysine (30 and 37 degrees C), L-valine, and gamma-aminobutyric acid into incubated mouse-cerebrum slices follows the rate equation for the initial influx of alpha-aminoisobutyric acid (Cohen, J. Physiol. 228:105, 1973), v equals Vmax/(1+Kt/S)+kuS. Kinetic constants at 37 degrees C are: Vmax equals 0.089 mumoles/g final wet wt of slices, min, Kt equals 0.69 mM, ku equals 0.037 mumoles/g final wet wt, mM-substrate, min for L-lysine; Vmax equals 0.60, Kt equals 1.30, ku equals 0.067 for L-valine; and Vmax equals 1.71, Kt equals 1.58, ku equals 0.094 for gamma-aminobutyric acid. The linear term, kuS, is due to an unsaturable process of concentrative uptake, not diffusion. Comparison of temperature coefficients reveals a "reference" pattern for typical low affinity transport of amino acids into brain slices. Its characteristics are: Activation energies associated with Vmax and ku are in range 14 to 20 kcal/mole; K, varies only slightly with temperature, L-Lysine and alpha-aminoisobutyric acid fit this pattern; L-valine and gamma-aminobutyric acid deviate in part. The Akedo-Christensen plot (J. Biol. Chem. 237:118, 1962) does not distinguish between the rateequation v equals Vmax/(1+Kt/S)+kuS for saturable uptake plus first-order unsaturable concentrative uptake, and the rate equation v equals Vmax/(1 + Kt/S)+kd(S minus Si) for saturable uptake plus first-order nonconcentrative "passive diffusion".
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D001921:Brain / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D051379:Mice; D051381:Rats; D013696:Temperature; D014633:Valine / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000621:Aminoisobutyric Acids; D005680:gamma-Aminobutyric Acid; D014633:Valine; D008239:Lysine