The rate equation and activation energies for the uptake of -aminoisobutyric acid by mouse brain slices.

1. The initial influx of the amino acid analogue AIB at medium concentrations of 0.05-20 mM into mouse cerebrum slices incubated at temperatures from 20 to 45 degrees C follows the rate law v = V(max)/(1 + K(t)/S)+k(u)S. The linear term k(u)S arises from an unsaturable process of concentrative uptake.2. At 37 degrees C the kinetic constants are K(t) = 1.12 mM; V(max) = 0.39 mumole AIB/g final wet wt. of slices. min; and k(u) = 0.054 mumole AIB/g final wet wt. of slices. mM-AIB. min.3. At infinitesmal substrate concentrations 13% of influx is via the unsaturable process. This rises to 73% for 20 mM substrate.4. K(t) is independent of temperature. The other constants increase rapidly with temperature. Arrhenius activation energies are 14.1 kcal/mole for V(max) and 17.4 kcal/mole for k(u).