Atypical Plasma Factor Associated with Bronchogenic Carcinoma and Complexing with R-Type Vitamin B12-Binding Proteins

Abstract

Human plasma contains three vitamin B₁₂ -binding proteins known as transcobalamin I, transcobalamin II and transcobalamin III.^{1 2 3 4} The first and third belong to the immunologically related class of R-type vitamin B₁₂-binding proteins and have apparent molecular weights of 150,000 daltons as determined by gel filtration. Transcobalamin II is immunologically distinct from transcobalamins I and III and has an apparent molecular weight of 38,000 daltons. In our studies of vitamin B₁₂-binding serum proteins, we found a patient with carcinoma of the bronchus in whom 90 per cent of the endogenous vitamin B₁₂ was in a . . .