I encountered this article which refers to alpha and beta b12-binding globulin. It says that in pernicious anemia patients their uptake of b12 is slower and they exhibit higher levels of b12 in the plasma because alpha gets first dibs on the b12 but is slower on the uptake (if I read it right). Now I've not heard of b12-binding globulins before. However I read this which suggests that they're just alternate names for transcobalamin 1 (haptocorrin) and transcobalamin 2. Now I just find it strange that haptocorrin, which is produced in the saliva and is meant to protect b12 from stomach acid until it can be transferred to the intrinsic factor in the gut, is what would need to be saturated in the plasma before transcobalamin 2 can access it. So I'm wondering if they aren't the same thing, or if the role of haptocorrin is larger than I thought. Of course it could just be a reading error on my part, that doesn't seem unlikely.