The Vitamin B₁₂ Binding Capacity of Transcobalamin I and II of Normal Human Serum

Abstract

The unsaturated serum vitamin B,, binding capacity (UB,,BC) of transcobalamin 0, I and I1 (TC 0, I and 11) of 50 normal subjects was determined by gel filtration on Sephadex G-200. TC 0 bound from 0 to 76 pg. per ml. of serum, accounting for up to 5.2 per cent of the UB,,BC, while TC I bound from 72 to 1057 pg. per ml., or up to 47.1 per cent of the UB,,BC. TC I1 bound from 650 to 1891 pg. per ml., accounting for up to 90.3 per cent of the UB,,BC.There was a significant positive correlation between the binding capacity of TC I and of TC I1 when each was compared with the total unsaturated B,, binding capacity. A positive correlation therefore existed between the binding capacity of TC I and that of TC 11. TC 0, I and I1 were the only binders of added B,, over a range from 75 to 20,760 pg. per ml. of serum. The relative amount of B,, bound to TC I and to TC I1 remained fairly constant in an individual serum regardless of the amount of B,, added.Abridgement of a thesis submitted by B.K.A. in fulfillment of the Fellowship of the

Vitamin B12‐Binding Proteins in Normal Human Blood Plasma and Serum

“…Of particularly great interest is the close correspondence between the present TC L values and the reported serum levels of the al-binder part of TC L (Lawrence 1969b) or the TC I part of TC L (Bloomfield & Scott 1972). Hom & Ahluwalia (1968) also commented upon the quantitative discrepancy between the UBBC of TC L in normal human serum and the earlier reported UBBC of the TC I or a-binder in normal human plasma or serum.…”

“…The denominations transcobalamin I (TC I) and transcobalamin I1 (TC 11), introduced for the two major vitamin B12-binding protein components in human blood plasma separated by ion gel exchange chromatography (Hall & Finkler 1965), have since been used also for the two major B12-binding serum components separated by gel filtration (Hom 1967, Hom & Ahluwalia 1968, Fi ler et al 1970, Hall & Wanko 1971.…”

“…Ths amounts of T C L demonstrated in human serum (Hom & Ahluwalia 1968, Lawrence 1969a/b, Gullberg 1970, Hall & Wanko 1971, Bloomfield & Scott 1972, Carmel 1972, Rachmilewitz et a1 1972 may poorly reflect the in vivo condition, since the technique for preparation of blood plasma or serum was found to influence greatly the amounts of recovered T C L, indicating that TC L is readily released in vitro from the blood cells (Gullberg 1971).…”

Vitamin B12‐Binding Proteins of R‐Type, Cobalophilin

“…In consequence of these changes due to the procedure, determinations of the unsaturated vitamin Blz-binding capacity of serum, and especially of cobalophilin in serum, give concentrations higher than those prevailing in vivo. Thus mean values of 330-766 ng/l (243-564 pmoV1) have been reported for serum (Hom & Ahluwalia 1968, Lawrence 1969b, and 57 f 37 ng/l(42 f 29 pmoVI), range 0-148 ng/l (0-109 pmoll 1)' for EDTA plasma (Gullberg 1972).…”

Vitamin B12 and Its Binding Proteins in Cirrhosis and Infectious Hepatitis

“…By different separation techniques it has been possible to separate one localised to the alphaglobulin fraction (TC I) and the other to the beta-globulin fraction (TC 11). By gel filtration on Sephadex G 200 a Bl,-binding protein in the macro-globulin fraction has been demonstrated (TCo) (Hom 1967, Hom & Ahluwalia 1968; and Hall & Finkler (1969) have by CM-cellulose chromatography isolated a fourth B12-binding protein which they state is specific for polycythaemia Vera.…”