Effect of temperature on kinetics and symmetries of the hexose transporter of Novikoff rat hepatoma cells.

We have used rapid kinetic techniques to measure the accumulation of radioactively labeled 3-O-methyl-D-glucose to transmembrane equilibrium in Novikoff cell suspensions as a function of temperature. Arrhenius plots of the maximum velocities of isotopic exchange and zero-trans entry were continuous between 6 and 39 degrees C (Ea = 15-19 kcal/mol). Equilibrium exchange and zero-trans entry of 3-O-methyl-glucose at six concentrations (1-30 mM) at 16, 27, and 35 degrees C conformed to appropriate integrated rate equations derived for a single transporter. The hexose transporter exhibited directional symmetry, but the loaded carrier moved about 2 times faster than the empty carrier at all three temperatures investigated. Thus, the differential mobilities of loaded and empty carrier are not affected by temperature in this range. The Michaelis--Menten constant for equilibrium exchange increased about 2-fold with increase in temperature between 16 and 35 degrees C.