The interaction of human transcobalamin isopeptides in cerebrospinal fluid and plasma with cobalamin and the cellular acceptor.
By isoelectric focusing, transcobalamin from human cerebrospinal fluid was separated into the phenotypes X, M, MX, SX and MS. The corresponding plasma transcobalamins were of identical phenotypes. The unsaturated cobalamin-binding capacity in the cerebrospinal fluid was 0.12-0.54 nmol.1(-1), median 0.23 nmol.1(-1); no difference in binding capacity was found between the individual phenotypes. The isopeptides M, X and S bound cyano[57Co]cobalamin from pH 6 to 10. The apparent affinity constant was the same for all the isopeptides (0.4.10(12) l.mol-1, pH 7.4). The isopeptide-cobalamin complexes bound to acceptors on human placenta membranes with an apparent affinity constant of 11.10(9) l.mol-1, pH 7.4.
Hansen
M
M
Department of Medicine and Haematology, Gentofte Hospital, University of Copenhagen, Denmark.
Nexø
E
E
D000328:Adult; D000368:Aged; D003038:Cobamides / Q000378:metabolism; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014155:Transcobalamins / Q000097:blood / Q000134:cerebrospinal fluid / Q000378:metabolism*; D014805:Vitamin B 12 / Q000378:metabolism*
D003038:Cobamides; D011956:Receptors, Cell Surface; D014155:Transcobalamins; C028176:transcobalamin receptor; C017142:cobinamide; D014805:Vitamin B 12