STUDIES ON THE ABSORPTION BY GUINEA PIG INTESTINE OF CYANOCOBALAMIN INCUBATED WITH INTRINSIC FACTOR*

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Abstract
Cyanocobalamin bound to human intrinsic factor is absorbed by the intact guinea pig, and is taken up by everted sacs of guinea pig intestine incubated in vitro. A portion of the cyanocobalamin present in the intestine of the intact guinea pig 5 hours after feeding, and of the cyanocobalamin taken up by incubated sacs of guinea pig intestine, can be removed by rinsing with EDTA, but not by rinsing with buffered saline. This EDTA soluble fraction is not in equilibrium with the cyanocobalamin which is not EDTA soluble. Cyanocobalamin incubated with intrinsic factor is incorporated into intestinal sacs incubated in vitro at a constant rate, which is reduced by certain metabolic inhibitors. The presence of 2, apparently independant, phases of cyanobalamin uptake by intestine may be due to microheterogeneity of intrinsic factor, or of the intestinal receptors to which the intrinsic factor binds.