Physical and binding properties of large fragments of human serum albumin

• Published in: Biochemical journal 1977-06, Vol.163 (3), p.477-484
• Main Authors: Geisow, M J, Beaven, G H
• Format: Article
• Language: English
• Subjects: Anilino Naphthalenesulfonates; Bilirubin; Binding Sites; Circular Dichroism; Humans; Hydrogen-Ion Concentration; Isomerism; Peptide Fragments - isolation & purification; Protein Binding; Serum Albumin - analysis; Tryptophan - analogs & derivatives
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj1630477

Three large fragments of human serum albumin were produced by peptic digestion of the native protein [Geisow & Beaven (1977) Biochem. J. 161, 619-625]. Fragment P44 represents residues 1-386 and fragments P29 and P31 represent residues 49-307 and residues 308-584 respectively of the albumin molecule. The large N-terminal fragment P44 has a similar percentage of alpha-helix to stored defatted albumin, although the alpha-helix content of all the fragments is significantly less than that of freshly prepared albumin. The fragment P44 appears to account for all the binding of the hydrophobic probe 8-anilinonaphthalene-1-sulphonate to albumin. N-Acetyl-L-tryptophan binds to this fragment and displaces one of the bound molecules of 8-anilinonaphthalene-1-sulphonate. Bilirubin binds to fragments P44 and P29, and the complexes show similar circular-dichroism spectra to that of the complex between bilirubin and whole albumin. These results are in agreement with affinity-labeling work on albumin with reactive ligands where substitution occurs in the N-terminal region of the molecule. The sharp conformational transitional transition in albumin which is observed between pH4 and 3.5 was absent from the fragments. This isomerization, usually called the N-F transition, probably occurs in intact albumin as a result of the unfolding or separation of the C-terminal third of the protein from the remainder of the molecule.