Transplacental transport in the rabbit of vitamin B12 bound to human transcobalamin I, II and III.
Transcobalamins I, II and III (TCI, TCII, TCIII) were purified from human serum, saturated with 57Co-vitamin B12 (57Co-B12), and injected into pregnant rabbits. Whole body retention of the 57Co-B12 averaged 91% and was similar for each of the three vitamin B12 binders. A maximum of 62% of the injected 57Co-B12 was found in fetal tissues when the vitamin was injected bound to TCII, but only 6--7% when bound to TCI or TCIII. Thus TCII is responsible for the delivery of vitamin B12 to the fetus.
D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D005260:Female; D005333:Fetus / Q000378:metabolism; D006801:Humans; D008431:Maternal-Fetal Exchange; D011247:Pregnancy; D011485:Protein Binding; D011817:Rabbits; D013997:Time Factors; D014155:Transcobalamins / Q000378:metabolism*; D014805:Vitamin B 12 / Q000378:metabolism*
D001798:Blood Proteins; D014155:Transcobalamins; D014805:Vitamin B 12