title: The interaction of human transcobalamin isopeptides in cerebrospinal fluid and plasma with cobalamin and the cellular acceptor.
abstract: 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.
authors.affiliation: Department of Medicine and Haematology, Gentofte Hospital, University of Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Hansen
authors.forename: E
authors.initials: E
authors.lastname: Nexø
mesh_terms: 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*
chemical_list: D003038:Cobamides; D011956:Receptors, Cell Surface; D014155:Transcobalamins; C028176:transcobalamin receptor; C017142:cobinamide; D014805:Vitamin B 12