A study of protein-binding in the metabolism of vitamin B12

Abstract

The natural vitamin B12 content and the binding capacity for cyanocobalamin of a number of tissues and body fluids of several animal species have been examined. As judged by electrophoresis, each material contained a specific cyanocobalamin-binding glycoprotein. The cyanocobalamin-protein complex obtained by adding the vitamin to chick serum has been isolated. Its properties were similar to those of the other 2 complexes (from milk and pig pylorus) we have studied. Although similar in some chemical and physical properties, the complexes from different sources had different availabilities for microorganisms and for animals and differed immunologically. The evidence for specific binding glycopro-teins playing an important role in the absorption and retention of cyanocobalamin in the body is discussed.