Kinetic Characterization of Apical <Emphasis Type="SmallCaps">D</Emphasis>-Fructose Transport in Chicken Jejunum

In mammals, D-fructose transport takes place across the brush-border membrane of the small intestine through GLUT5, a member of the facilitative glucose transporter family. In the present paper, we describe and characterize for the first time the apical transport of D-fructose in chicken intestine. Brush-border membrane vesicles (BBMV) were obtained from jejunum of 5- to 6-wk-old chickens. D-Fructose uptake by BBMV from chicken jejunum comprises a saturable component and a simple diffusion process. The maximal rate of transport (V_max) for D-fructose was 2.49 nmol·(mg prot)^–1·s^–1, the Michaelis constant (K_m) was 29 mM, and the diffusion constant (K_d) was 25 nl·(mg prot)^–1·s^–1. The apical transport of D-fructose was Na⁺-independent, phlorizin-, phloretin-, and cytochalasin B-insensitive, and did not show cis-inhibition by D-glucose or D-galactose. These properties, together with the detection of specific GLUT5 mRNA, indicate the presence of a low-affinity high-capacity GLUT5-type carrier in the chicken jejunum, responsible for the entry of D-fructose across the brush-border membrane of enterocytes.