Enzymes involved in protein transmission by the intestine of the newborn lamb.

The intestine of lambs killed immediately after birth and at intervals after the first feed was studied by electron microscope cytochemistry. Ferritin, incorporated into this feed, was found within 2 h of feeding within vesicles throughout the cytoplasm of enterocytes lining the proximal and mid-intestine. Some of these vesicles had fused with the lateral and basal membranes of the enterocytes. Histochemical reaction products for alkaline phosphatase and a series of lysosomal enzymes were localized within the vesicles; the distribution of acid hydrolases, however, was not uniform within each cell. Biochemical estimations of the activity of these enzymes showed greatest activity in the distal intestine of the newborn lamb. The activity of only one of these enzymes, N-acetyl-beta-glucosaminidase, was maximal in the mid-intestine. These observations indicate that cytoplasmic vesicles, translocating proteins across the enterocyte, probably carry intestinal alkaline phosphatase activity in their limiting membrane. Lysosomal enzymes, particularly glucosaminidase, are introduced into these vesicles as they traverse the enterocytes of the mid-intestine. A less specialized complement of lysosomal enzymes is probably introduced into vesicles in the distal intestine where ingested protein may be digested, rather than transported across the cell.