A comparison of the rate equations, kinetic parameters, and activation energies for the initial uptake ofl-lysine,l-valine, γ-aminobutyric acid, and α-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".

Derepression of Amino Acid-H+ Cotransport in Developing Soybean Embryos

“…The unnatural amino acid, AIB, has been used often to study amino acid transport mechanisms without interference from metabolism of the transported substrate (1,15,18). We were interested in calculating accumulation ratios (cytoplasmic concentration/external concentration) of a transported amino acid and so used AIB here.…”

Potassium Transport in Corn Roots

“…He argues that many of the frequently cited discontinuous uptake isotherms could be explained by models consisting of one or more Michaelis-Menten terms plus a linear term, particularly if experimental error and biological variability are considered. The existence of this linear term has often been ignored, despite the fact that transport kinetics consisting of Michaelis-Menten and linear terms have been well documented in both plant and animal systems (3,5,8,9,13,20,22,27,28,32 …”

The complete rate equation, including the explicit dependence on Na+ ions, for the influx of α-aminoisobutyric acid into mouse brain slices

“…(1)] for saturable and unsaturable transport is parallel has been found for the uptake of several amino acids by brain slices incubated under a variety of conditions: AIB at temperatures from 20 to 45 ~ (Cohen, 1973), L-valine and GABA at 25 and 37 ~ L-lysine at 30 and 37 ~ (Cohen, 1975) and L-leucine at 37 ~ (S.R. Cohen, unpublished), all from standardmedium; AIB at 37 ~ and GABA at 25 and 37 ~ from a medium (Na-138/ pyruvate) containing sodium pyruvate instead of glucose as the energy source (S.R.…”

“…: 119 mM NaC1, 5.0mM KC1, 0.75 mM CaCI2, 1.2 mM MgSO4, 1.0 mM NaH2PO~, 1.0 mM NaHCO3, 25 mM HEPES, 12 mM NaOH (which reacts to form the complementary base of the buffer), and 10 mM glucose. This medium ) was used in our earlier studies (Cohen, 1973(Cohen, , 1975 Curve Fitting and Precision. Eqs.…”

“…This component is also an important pathway for AIB influx from standard medium at temperatures from 20 to 45 ~ (Cohen, 1973) and from Na-t38/pyruvate medium (S.R. Cohen, in preparation), and for the influx of a number of amino acids into preparations of various tissues and isolated cells (Cohen, 1973(Cohen, , 1975.…”