Measurement of vitamin B12-binding proteins of plasma. I. Technique
JA Begley and CA Hall
The unsaturated binding capacities (UBBC) of individual vitamin B12-
binding proteins in plasma were measured by a two-step procedure.
Transcobalamin II (TC II) was separated by precipitation with ammonium
sulfate; the "R"-type binders remaining soluble were then divided into two
components by bath separation with anion exchange on DEAE- cellulose. The
two R components were designated alpha1-R (TC 1) and alpha2-R (third
binder, fetal binder, PV binder, TC III). Ten normal sera were studied by
this technique giving a separation into TC III and total plasma R identical
to that obtained simultaneously by gel filtration. The mean UBBC of TC II
was 969 plus or minus 204 pg of 57 Co B12 per ml of serum. The mean
contamination of the precipitated TC III with plasma R was 3%. The UBBCs of
alpha 2-R and alpha 1-R were 127 plus or minus 42 and 40 plus or minus 12
pg/ml, respectively. The mean contamination of the R fraction by TC II was
14% as evaluated by gel filtration. By isoelectric focusing it was found
that the alpha1-R contained principally those components isoelectric at pH
isoelectric at pH of 2.9-3.2, while alpha2-R was made up of those
components isoelectric at pH of 3.6 or greater.
Volume 45,
Issue 2,
pp. 281-286,
02/01/1975
Copyright © 1975 by The American Society of Hematology
