title: Photodynamic protein cross-linking.
abstract: Exposure of spectrin to visible light in the presence of a photosensitizer results in photo-oxidation of sensitive amino acid residues and covalent cross-linking of the polypeptides. In a previous paper the cross-linking was ascribed to a secondary reaction between photo-oxidized histidine residues and amino groups. The following observations, described in this paper, are in accordance with this supposition. (1) During illumination of spectrin in the presence of a photosensitizer a pronounced photo-oxidation of histidine residues takes place. (2) Simultaneously a decrease of free amino groups is observed. (3) Semicarbazide protects against cross-linking and is bound to a histidine photo-oxidation product in spectrin. (4) The pH profile of histidine photo-oxidation and subsequent reaction with amino groups is similar to the pH profile of spectrin cross-linking. Amidination of NH2 groups in spectrin does not inhibit cross-linking, as visualized by gel electrophoresis. On the other hand aminidation of denatured myoglobin causes a 50% inhibition of cross-linking. These observations support the notion of NH2-involvement in cross-linking but also demonstrate, that other photodynamic cross-link mechanisms exist.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism; D010777:Photochemistry; D011524:Protoporphyrins / Q000378:metabolism; D012663:Semicarbazides / Q000378:metabolism; D013049:Spectrin / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D003432:Cross-Linking Reagents; D008565:Membrane Proteins; D009211:Myoglobin; D011524:Protoporphyrins; D012663:Semicarbazides; D013049:Spectrin; D005998:Glycine