Kinetic characterization of apical D-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.