Interaction of Phlorizin and phloretin with glucose transport system of the pigeon intestine

Interaction of phlorizin and phloretin with in vitro transport of D-[U-¹⁴C]glucose in the pigeon small intestine has been investigated. Phlorizin readily inhibits D-glucose uptake in the presence (not absence) of Na⁺ ions as well as in the presence and absence of Na⁺ gradient. In contrast, phloretin has no immidiate effect on glucose uptake both in the presence and absence of Na⁺ ions as well as in the presence and absence of Na⁺ gradient. However, it enhances the equilibrium level of glucose binding to mucosal tissue by two-fold and affects the sugar only when tissues are preincubated with it. The kinetic analysis of phlorizin/phloretin interference with glucose transport yields parallel lines. The calculated inhibitory constant (K(i)) values are 5.5 μmole and 0.28 m M respectively for phlorizin and phloretin. It is possibe that (i) phlorizin and phloretin mutually compete for available binding sites on the glucose transporter of brush border membrane and (ii) a phenol binding site is involved in the normal maintenance of glucose transport rate.