Intrinsic factor mediated cobalamin absorption

The physiological absorption of vitamin B₁₂ is a complex process which requires the interaction of several macromolecules. Mediated by the glycoprotein, intrinsic factor (IF), this process requires formation of a primary complex between vitamin B₁₂ and IF (IF-B₁₂), the recognition and binding of this complex to specific ileal receptors and the transport of vitamin B₁₂ across the ileal cell. As a measure of this overall process, the vitamin B₁₂ absorption test has helped to identify abnormal vitamin B₁₂ absorption in patients with exocrine pancreatic insufficiency and familial vitamin B₁₂ malabsorption (Immerslung-Grasbeck syndrome). Progress into understanding the role of proteolytic enzymes in promoting vitamin B₁₂ absorption as well as the molecular events of vitamin B₁₂ transport across the ileal cell has been brought about by recent investigation based upon this determination.