Cobalamin and its binding protein in rat milk

Abstract

Cobalamin and its binding protein, haptocorrin, are present in rat milk throughout the lactation period. The concentration of cobalamin is approximately 0.3-times the concentration of the unsaturated binding protein. The concentration of the unsaturated cobalamin-binding protein varies between 18 nmol l^-1 and 61 nmol 1^-1. The binding protein has a Stokes radius of 2.49 nm when saturated with cobalamin and 2.61 nm when unsaturated. It binds cobalamin over a broad range of pH and is able to bind cobinamide also. With immunohistochemistry, we find haptocorrin immunoreactivity in the mammary glands and in the sebaceous glands of the nipple.

Key Words:

• cobalamin
• cobalamin-binding protein
• haptocorrin
• milk (rat)
• vitamin B₁₂