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. 1. A sodium-dependent and a sodium-independent component of d-glucose uptake are observed. The sodium-dependent component is phlorizin sensitive ( K I ≈ 0.6 μM) and electrogenic. 2. 2. The sodium-dependent component of d-glucose uptake yields non-linear Eadie-Hofstee plots consistent with the presence of high (G H) and low (G L) affinity sites ( K H ≈ 0.2 mM, K L ≈ 4.5 mM, V L/ V H ≈ 7 at pH 7.4, 25°C, 100 mM NaCl gradient). Alternative explanations are cooperative effects or non-Michaelis-Menten kinetics. 3. 3. The initial uptake of d-glucose increases as the intravesicular membrane potential become more negative but the numerical values of K H and K L show little, if any, change. 4. 4. α- Methyl- d- glucoside transport is also sodium dependent and phlorizin sensitive ( K I ≈ 1.9 μM). 5. 5. In contrast to the results for d-glucose, the sodium-dependent component of α-methyl- d-glucoside uptake exhibits a nearly linear Eadie-Hofstee plot consistent with a single carrier site with K m ≈ 1.9 mM and V max ≈ 27 nmol/min per mg protein at pH 7.4, 25°C, 100 NaCl gradient. 6. 6. The kinetics of d-glucose transport in newborn dog kidney are similar to those in the adult except that the low affinity (G L) system appears to be less well developed.