Sugar uptake into brush border vesicles from dog kidney. II. Kinetics

Abstract

The kinetics of D-glucose transport over the concentration range 0.07--20 mM have been investigated in a vesiculated membrane preparation from dog kidney cortex. 1. A sodium-dependent and a sodium-independent component of D-glucose uptake are observed. The sodium-dependent component is phlorizin sensitive (KI approximately 0.6 micron) and electrogenic. 2. The sodium-dependent component of D-glucose uptake yields non-linear Eadie-Hofstee plots consistent with the presence of high (GH) and low (GL) affinity sites (KH approximately 0.2 mM, KL approximately 4.5 mM, VL/VH approximately 7 at pH 7.4, 25 degrees C, 100 mM NaC1 gradient). Alternative explanations are cooperative effects of non-Michaelis-Menten kinetics. 3. The initial uptake of D-glucose increases as the intravesicular membrane potential become more negative but the numerical values of KH and KL show little, if any, change. 4. alpha-Methyl-D-glucoside transport is also sodium dependent and phlorizin sensitive (KI approximately 1.9 micron). 5. In contrast to the results for D-glucose, the sodium-dependent component of alpha-methyl-D-glucoside uptake exhibits a nearly linear Eadie-Hofstee plot consistent with a single carrier site with Km approximately 1.9 mM and Vmax approximately 27 nmol/min per mg protein at pH 7.4, 25 degrees C, 100 mM NaCl gradient. 6. The kinetics of D-glucose transport in newborn dog kidney are similar to those in the adult except that the low affinity (GL) system appears to be less well developed.