There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Role of Transcobalamin in Vitamin B12 Transport
- Transcobalamin (TC) plays a crucial role in the transport of vitamin B12 (cobalamin) from plasma to cells 1, 2, 3, 4.
- TC deficiency is a rare autosomal recessive disorder that results in the unavailability of cobalamin in cells, leading to accumulation of homocysteine and methylmalonic acid 1, 4.
- The transport process involves the uptake of transcobalamin-bound vitamin B12 by cells, which is dependent on the presence of calcium ions, cellular respiration, and free sulphydryl groups 2.
- All three transcobalamins (I, II, and III) play a role in the transfer of vitamin B12 to tissue cells 2.
- Transcobalamin II (TC II) and its cell surface receptor (TC II-R) are essential components of plasma cobalamin transport to all cells 3.
Mechanism of Transcobalamin-Mediated Transport
- Transcobalamin recognizes and transports glutathionylcobalamin (GSCbl), a naturally occurring form of vitamin B12, equally well as aquo/hydroxocobalamin 5.
- The residues involved in the recognition and transport of GSCbl are conserved among TCs from different organisms 5.
- Haptocorrin and intrinsic factor are not structurally tailored to bind GSCbl, suggesting a specific role for TC in the transport of this form of vitamin B12 5.
Clinical Implications of Transcobalamin Deficiency
- Transcobalamin deficiency can cause megaloblastic bone marrow failure, accumulation of homocysteine and methylmalonic acid, and methionine depletion 4.
- Early detection and aggressive treatment of TC deficiency are necessary to prevent severe neuro-ophthalmological impairment and other complications 4.