Complexing of transcobalamin 2 and apparent combination with heparin.

. which have been named transcobalamin 1 and 2 by Hall and Finkler.4 \Vhen serum which contains radioactive vitamin B12 is filtered through sephadex, the radioactivity appears in the effluent in fractions corresponding to molecular weights of 121,000 and 36,000. It has been assumed that these fractions correspond to association of the B12 with TC1 and TC2, respectively. It has been reported that the fraction of larger molecular weight is heterogeneous when chromatographed on DEAE cellulose,7 and that in plasma from some patients, the apparent size of TC2 is increased, possibly due to antibody to this material.8 \Ve have reported that plasma from human portal venous blood obtained through the umbilical vein during absorption of 5 CoB12 contained no fraction with molecular weight of 36,000 when filtering through sephadex,9 but its affinity for DEAE cellulose was found subsequently to he identical with that of TC2. Because the portal blood contained heparin, and we have observed that the distribution of B12 in fractions obtained when serum was filtered through sephadex differed from that when plasma from heparinized or EDTA blood was filtered, we have studied the effect of heparin and EDTA on the B12 binders in human plasma and serum. Heparin has been reported to alter B12 binding by plasma.’#{176}’11 Blood was obtained from patients undergoing venepuncture for the control of anticoagulant therapy, and from volunteer normal subjects. The effect of heparin and of EDTA on the filtration patterns of pools of serum and plasma and of plasma from different individual normal subjects was similar. For convenience, all studies illustrated in the figures in this paper utilized blood from a single normal subject.