Vitamin B12-binding proteins of the horseshoe crab Limulus polyphemus.
Vitamin B12-binding proteins were detected in the body fluids and/or tissues of horseshoe crabs (Limulus polyphemus), clams and sponges. Among the biological specimens tested the Limulus plasma was especially rich in free B12-binding proteins. Gel filtration experiments revealed that Limulus plasma contains two classes of B12-binding proteins. One class of proteins, molecular weight in excess of 100,000, bind B12 preferentially with affinity constant of 5 X 10(11)M-1. The second type of proteins, molecular weights around 50,000, bind B12 with specificity approaching that of mammalian intrinsic factors. The binding constant of these proteins for B12 is around 10(11)M-1.
D000818:Animals; D003386:Brachyura; D002850:Chromatography, Gel; D008970:Molecular Weight; D014155:Transcobalamins / Q000032:analysis*
D014155:Transcobalamins