Abstract
The intestinal transport of the naturally occurring folate coenzyme, 5-methyltetrahydrofolate, was studied using everted sacs of rat jejunum. The study provides evidence that intestinal transport of 5-methyltetrahydrofolate is composed of two systems: 1) an active, carrier-mediated system which is demonstrable at low concentrations; and 2) a diffusion system which is demonstrable at high concentrations. These studies clarify the mechanism of intestinal transport of 5-methyltetrahydrofolate, show the similarities to transport of other folate compounds and provide a unified concept of intestinal folate transport.