Evidence against transferrin as a binder of either vitamin B12 or folic acid.

S EVERAL REPORTS RAISED the possibility that transferrin might be a carrier protein for both vitamin B,2 and for folic acid. In 1972, Carmel and Herbert’ reported that B,2-binding protein from leukocyte sonicates electrophoresed at pH 8.6 at the same mobility as transferrin, and in 1973, Sam uels et al.2 reported that some radioactive B12 bound to a material which moved with the speed of transferrin in disk acrylamide electrophoresis of serum and of a 95#{176}/a pure preparation of transferrin. A further suspicion of relation between a vitamin B12-binding protein and transferrin is raised by the reports3’4 that unsaturated vitamin B,2-binding capacity is elevated with iron deficiency. In 1972, Markkanen et al.5reported that transferrin was a carrier protein for folic acid activity, using horizontal starch gel electrophoresis of human serum, and in 1973, Waxman and Schreiber reported that a folic acid-binding protein moved with the speed oftransferrin in their system.6 Studies were carried out to evaluate directly whether transferrin in fact was a carrier protein for either vitamin B,2 or folic acid.