Flash photolysis study of insulin.
The transient absorption spectra of the initial UV-photolysis products of insulin and des-pentapeptide (B26-30)-insulin (DPI) were determined and compared with that of free tyrosine. The far-UV band of the spectra (less than 300 nm) has not been reported before. Their main initial photoproducts are p-alanylphenoxyl radical (lambda max = 410,390 nm) and an unidentified radical (lambda max = 270 nm). The photolysis yields are closely correlative with the dissociation rate of hydroxyl group on phenol ring of tyrosine residues, which in turn depends on the exposed degree of these residues. The quantum yields of the phenoxyl radicals formed in photolysis of insulin and DPI were determined and compared with that of free tyrosine. Based on the comparison, the number of light accessible tyrosine residue in insulin and DPI can be calculated, which provides more quantitative information on the exposed degree of tyrosine residues in these two proteins.
D006863:Hydrogen-Ion Concentration; D007328:Insulin; D010782:Photolysis; D011487:Protein Conformation; D014443:Tyrosine
D007328:Insulin; D014443:Tyrosine