B12 is released from dietary proteins by which gastric factors?

• A. Amylase and lipase
• B. Bile and bicarbonate
• C. Mucus and water
• D. HCl and pepsin

Answer: (D)

B12 release from dietary proteins in the stomach requires acid-activated proteolysis. In the stomach, hydrochloric acid denatures the dietary proteins and activates pepsin, the protease that digests them. This proteolysis frees vitamin B12 from the protein complex so it can later bind to R-binding protein and eventually intrinsic factor. Other options don’t accomplish this: amylase and lipase digest carbohydrates and fats; bile and bicarbonate function mainly in the small intestine; mucus and water don’t liberate B12.