Gel Filtration Studies of Serum B₁₂ Binding: An Abnormal Pattern in Patients with Vitamin B₁₂ Deficiency

⁵⁷CoB₁₂ was added to serum in vitro to study its binding by the three known serum B₁₂-binders in patients with vitamin B₁₂ deficiency and in normal controls. Gel filtration through columns of Sephadex G-200 was used to separate the low (beta) and high (alpha₁ and beta) molecular weight B₁₂-binding fractions. Electrophoresis on filter paper was used to separate the alpha₁- and beta-globulins.

The alpha₁-globulin fraction in the serum of B₁₂-deficient patients bound more of the added ⁵⁷CoB₁₂ than did this fraction in normal serum, presumably because this binder of the serum endogenous vitamin B₁₂ is much less saturated in B₁₂-deficiency. However, the total B₁₂ binding capacity of the alpha₁-globulin (for endogenous plus added vitamin B₁₂) was lower in B₁₂-deficient than in normal serum.

The low molecular weight beta-binder bound more added ⁵⁷CoB₁₂ in B₁₂-deficient than in normal serum, whereas the high molecular weight beta binder had a much lower B₁₂-binding capacity in deficient than in normal serum. These abnormalities were independent of the cause of the vitamin B₁₂ deficiency and disappeared after successful treatment with vitamin B₁₂.