Vitamin B12 binders of chicken serum and chicken proventriculus are immunologically similar.

Two substances that bind vitamin B(l2) are found in chickens, one in the serum and another in the proventriculus. Their molecular weights, as estimated from gel filtration on Sephadex, are approximately 113,000 and 96,000, respectively. Antibody elicitedin ratsagainst the proventriculus binder reacts against both binders.