Photooxidation of specific residues in alpha-crystallin polypeptides

Biochemistry. 1991 Sep 3;30(35):8653-60. doi: 10.1021/bi00099a023.


Singlet oxygen is a biologically important, photochemically generated species that preferentially oxidizes His, Trp, and Met residues of protein molecules. Calf alpha-crystallin was photooxidized with use of meso-tetra(p-sulfonatophenyl)porphyrin (TPPS) and uroporphyrin (UP) as singlet oxygen generators. The effects of photooxidation were monitored by analyzing the changes in alpha-crystallin peptide maps obtained by reversed-phase HPLC using a photodiode array absorbance detector. The reaction led to the loss of six specific peptides, five of which contained photooxidizable residues. Peptides containing His-97 and His-154 from the A chain and Met-68 from the B chain are preferentially photooxidized, suggesting that those residues have access to singlet oxygen. Trp residues in the N-terminal region are converted to NFK, whereas Trp-60 in the B chain is not photooxidized strongly suggesting that the former are close to the surface of alpha-crystallin while the latter Trp residue is buried. Only one peptide that is lost from the peptide maps does not contain a photooxidizable group; however, this peptide does contain an apparently undigested Lys residue. It is suggested that it forms a cross-link with a photooxidized His residue.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cattle
  • Chromatography, High Pressure Liquid
  • Crystallins / metabolism*
  • Molecular Sequence Data
  • Peptide Fragments / chemistry*
  • Peptide Fragments / isolation & purification
  • Peptide Mapping
  • Photolysis*
  • Protein Conformation
  • Trypsin


  • Crystallins
  • Peptide Fragments
  • Trypsin