Is the brush border membrane of the intestinal mucosa a generator of "chymosomes"?

1. The microvilli of enterocytes in calf intestine demonstrate high levels of vesiculation activity at the top and at the basal region. 2. The morphology of the vesicles associated with microvilli (100-500 nm diameter, unilamellar, few intramembraneous particles, high AP activity) is very similar to the morphology of vesicles found in the chyme. 3. Vesicles can be purified 6-10 fold from chyme of the calf intestine applying a Mg(++)-precipitation method, used for brush border membrane preparation. 4. Specific activities of alkaline phosphatase and disaccharidases were found to be much higher in chyme vesicles than in the mucosa. 5. Phospholipid content and phospholipid composition is in chyme vesicles different from brush border membrane vesicles. 6. The characterized chyme vesicles are referred to as chymosomes. We consider the mucosa as a large-scale generator of chymosomes, i.e. digestive enzymes bearing vesicles.