Comparison of folate conjugase activities in human, pig, rat and monkey intestine

Folate conjugase, an intestinal enzyme that hydrolyzes dietary polyglutamyl folate to the absorbable monoglutamyl derivative, is present in two locations in human jejunal mucosa: one on the brush border membrane, the other soluble and intracellar. Although the brush border enzyme has not been found in the rodent, a recent study demonstrated both brush border and intracellular folate conjugases in the pig with properties similar to the human enzymes. To confirm and expand these data, we compared folate conjugase activities in intestinal brush border and 30,000 X g supernatant fractions in human, pig, rat and monkey mucosa. In both the human and pig, brush border folate conjugase was active from pH 4.5 to 8.5, and activity was significantly increased by zinc acetate. In contrast, folate conjugase activity was negligible in rat and monkey mucosal brush borders. Intracellular folate conjugase was maximally active at pH 4.5 in the human, pig and monkey, whereas this enzyme was equally active from pH 4.0 to 7.5 in the rat. In each species, supernatant activity at pH 4.5 was completely inhibited by p-hydroxymercuribenzoate. Although folate conjugase was quantitatively more active in the human than in the pig intestine, the brush border and intracellular enzymes exhibited similar properties. Sucrase, lactase and aminopeptidase activities were also similar in the two species. Our data show marked species differences in mucosal folate conjugase activities and indicate that the pig may be a suitable experimental animal for further studies of folate hydrolysis and absorption in humans.