Effect of pH on Intrinsic Factor and Nonintrinsic Factor Vitamin B12 Binding in Human Gastric Juice Neutralized in Vivo

Abstract

The effect of an acid environment on the quantification of the vitamin B12-binding substances of normal human gastric juice collected by in vivo neutralization has been studied in 7 subjects. A progressive decline in both intrinsic factor and nonintrinsic factor B12 binding, as measured by immunoassay with increasing exposure to an acid pH, has been demonstrated. Reduction in intrinsic factor B12 binding occurred over a wide range of initial intrinsic factor activity and was significant after 10 to 15 min of exposure to an acid pH. An average reduction in intrinsic factor activity of 20% after 15 min, increasing to 38% after 1 hr of exposure, was observed. The B12 binding of partially purified human intrinsic factor which did not possess peptic activity was not affected by acidification, indicating that the effect in gastric juice is probably a proteolytic one. These observations emphasize the importance of attempting to eliminate autodigestive effects by the use of in vivo neutralization in any quantitative study of gastric intrinsic factor secretion.