Molecular organization of the sex steroid-binding protein (SBP) of human plasma.
Several years ago this laboratory presented evidence that SBP is a dimer composed of two subunits having similar molecular weights. The question of whether or not these subunits are identical and therefore products of a single gene remained unanswered. We now report that the two polypeptide chains are identical and that SBP is a homodimer. The experimental approach was to reduce and [14C]alkylate cystine residues in human SBP, digest the product with trypsin or cyanogen bromide and determine the number of unique amino acid sequences around each [14C]carboxymethylcysteine residue. Only four unique sequences were found when all the radioactive peptides were analyzed. Since there are eight half-cystine residues per dimer, the results support a homodimeric structure.
P H
PH
Petra
S
S
Kumar
R
R
Hayes
L H
LH
Ericsson
K
K
Titani
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D003488:Cyanogen Bromide / Q000494:pharmacology; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis; D011487:Protein Conformation; D012738:Sex Hormone-Binding Globulin / Q000032:analysis*; D014357:Trypsin / Q000494:pharmacology
D000596:Amino Acids; D010446:Peptide Fragments; D012738:Sex Hormone-Binding Globulin; D014357:Trypsin; D003488:Cyanogen Bromide