J. Biol. Chem., Vol. 265, Issue 16, 9066-9071, Jun, 1990
Location of dehydroalanine residues in the amino acid sequence of bovine thyroglobulin. Identification of "donor" tyrosine sites for hormonogenesis in thyroglobulin
Y Ohmiya, H Hayashi, T Kondo and Y Kondo
Department of Physical Biochemistry, Gunma University, Maebashi, Japan.
Thyroid hormonogenesis in thyroglobulin results in the conversion of an
"acceptor" iodotyrosine to a hormone residue and a "donor" iodotyrosine to
a dehydroalanine residue. Altogether five acceptor sites have been located
as hormone residues in thyroglobulin of different animal species. To search
for donor sites, we treated bovine thyroglobulin with 4-aminothiophenol to
specifically modify dehydroalanine residues to S-(4-aminophenyl)cysteine
(APC) residues, according to the principle of dehydroalanine determination
developed by us (Kondo, T., Kondo, Y., and Ui, N. (1988) Mol. Cell. Endocr.
57, 101-106). After digesting thyroglobulin with lysyl endopeptidase,
APC-containing peptides were separated from other peptides by trapping them
on immobilized naphthylethylenediamine and from each other by
size-exclusion and reverse-phase high performance liquid chromatography
(HPLC). The HPLC patterns showed about 10 APC-containing peptides. Among
them, four different peptides were purified by repeated reverse-phase HPLC.
The results of partial sequencing of the four peptides by manual Edman
degradation disclosed that Tyr5, Tyr926, Tyr1375, and Tyr986 or Tyr1008 are
available for hormonogenesis as donor sites. These results strongly suggest
that only specific tyrosine residues behave as donors.