The effect of proteolytic enzymes on the vitamin B12-binding proteins of human gastric juice and saliva.

Pepsin had no effect on the vitamin B12 binder in human saliva (R-binder), while trypsin was found to reduce the apparent molecular weight of the R-binder and to release vitamin B12 from the R-B12complex of human saliva and human gastric juice (HGJ). Trypsin had no effect on the molecular weight and biological activity of intrinsic factor (IF) in HGJ, as demonstrated by gel filtration on Sephadex G-150 and the uptake of IF-B12 by guinea pig intestinal brush borders. An extract of purified guinea pig intestinal lysosomes was also without effect on the molecular weight and the biological activity of IF but was found to release vitamin B12 from the R-B12 complex. The results support the observation that the external pancreatic secretion corrects malabsorption of vitamin B12 by an effect on the non-IF protein in the intestinal juice. Moreover, the results indicate that lysosomal enzymes are not involved in the intestinal absorption of vitamin B12.