Kinetics of the mediated transport and the passive net flux of phenylalanine across the rat small intestine in vivo

Abstract

The kinetics of L-phenylalanine absorption by rat jejunum, in vivo, has been studied with luminal perfusion (0.68 ml/min) during successive periods at different substrate concentrations.The non-saturable passive component, measured by inhibiting the active transport with 60 mM methionine, was a linear function of the substrate concentration with an apparent mass-transfer coefficient of 1.42 nmoles/cm/min/mmoles/l.The transport component, estimated from the difference between total absorption and the passive component, displays saturation kinetics with an apparent transport constant (Km) of 7.5 mM and maximal transport rate (Vmax) of 107 nmoles/cm/min.Active transport seems to be the main component in absorbing phenylalanine proceeding from the digestion of food proteins.