JBC, Vol. 250, Issue 17, 6711-6719, Sep, 1975
Positions in human serum albumin which involve the indole binding site. Sequence of 107-residue fragment
K. K. Gambhir, R. H. McMenamy and F. Watson
The first 107 residues of Fragment C of human serum albumin have been
sequenced and two positions at which affinity labels block the indole site
determined. Histidine 23 is the position of blockage by
bromoacetyl-L-tryptophan and lysine 67 is the position of blockage by
5-dimethylaminonaphthalene-1-sulfonyl chloride and probably
pyridoxal-5'-phosphate. The presence of an indole ligand at the binding
site markedly reduces incorporation of the label into the above lysyl
residue, and in the case of 5-dimethylaminonaphthalene-1-sulfonyl chloride,
increases incorporation into three other positions, lysine residues 13, 39,
and 84. It is concluded that binding of the indole ligand on the site
brings about conformational changes in the albumin structure exposing new
reactive positions for 5-dimethylaminonaphthalene-1-sulfonyl chloride.
There is a large accumulation of basic and hydrophobic residues and no
glycine, serine, threonine, valine, aspartate, or cysteine residues in the
sequence 10 to 43. Lysine 71 has been identified by amino acid analyses and
sequence studies as the position acetylated by acetylsalicylic acid
(Hawkins, D. R., Pinckard, N., Crawford, C. P., and Farr, R. S. J. Clin.
Invest. (1969) 48, 536), establishing the structural relationships of two
major ligand binding sites on albumin. The lone tryptophan is at position
86. Evidence indicates that within residues 1 to 86 of Fragment C and
within residues of the A-Phe fragment (Mr equals approximately 10,000), the
latter known to be adjacent to Fragment C in the whole albumin structure,
exists the major binding sites of all ligands for human serum albumin.
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