D-xylose: active intestinal transport in a sodium ion substituted lithium medium.

Abstract

IT is becoming increasingly evident that the active transport of a wide variety of substances by the small intestine requires sodium ions1–4. The mechanism of active sugar transport, postulated by Crane5,6, accounts for the movement of a sugar against its own concentration gradient by virtue of an opposing sodium ion gradient. D-xylose is the only pentose which has been demonstrated to be actively transported by the small intestine7 and it has been suggested that its mechanism of transport is similar to that of the hexoses8. A criterion used to arrive at this conclusion was the apparent dependency of active D-xylose transport on sodium ions.