Intestinal uptake and release of XXXX complexed with rat @entity72783 .

@entity72783 @entity2187 @entity95 @entity2186 @entity141 @entity503
The mechanism of uptake of @entity72783 ( @entity72783 ) and @entity2186 ( @entity2187 ) by enterocytes and their subsequent fate have been uncertain. To examine this problem double-labeled IF X @entity2187 was added to small intestinal organ cultures. When 125I-IF X [57Co]Cbl was added to @entity95 ileal explants, binding and internalization increased linearly for 24 h. After an 18-h chase with nonlabeled IF X @entity2187 , no 125I-IF returned to the cell surface. An amount of 35-45% of the internalized @entity2187 was found free, not bound to @entity72783 or any other protein. About 60% of both internalized ligands was bound to membranes but by a non- @entity141 -dependent bond, suggesting binding to a protein other than the brush-border receptor. @entity2186 was released from @entity72783 at pH 5.0 to the same degree (30%) as free @entity2187 was found inside the cell (35-45%). Neither pancreatic proteases nor ileal homogenates effected release of @entity2187 from @entity72783 . When cathepsins were added, the @entity2187 released was no greater than could be attributed to pH 5.0 alone. @entity503 added to tissue explants did not alter the percentage of free intracellular @entity2187 . From these results we suggest that IF X @entity2187 is internalized and detached from the receptor within the enterocyte. The mechanism of release is not known but seems to require an acid pH (5.0). The @entity2187 is released in the mucosa, perhaps when the IF X @entity2187 complex enters a nonlysosomal cellular compartment with an acidic environment. There is no substantial recycling of @entity72783 to the brush-border membrane.
