[The intraluminal transport of vitamin B12]

Abstract

Since the existence of vitamin B12 was suggested by Castle in the first few decades of this century, vitamin B12 has been the subject of many studies which have proved the high complexity of its assimilation by the organism. Over the last few years the marked progress in functional digestive exploration methods and the physical and the chemical characteristics of biological molecules have revived the established idea of the vitamin's intraluminal transit. Our recent studies have been concentrated on the bilio-duodenopancreatic stage of the vitamin B12 transport. In nature, vitamin B12 is only exceptionally met in its free form, it is always associated with a binder. Like a ball being passed from one player to another it moves between binders. Alimentary vitamin B12 released from its protein complexes by culinary preparation and gastric secretions, is combined with haptocorrin. In the duodenum the transfer of B12 on intrinsic factor is due to partial degradation of haptocorrin by pancreatic enzymes and intraluminal pH balance. Then combined with intrinsic factor the vitamin can be caught by the ileal receptor. The partial degradation haptocorrin joins vitamin B12 analogs from excreted bile or synthesized by the intestinal microorganisms.