| 摘 要： | 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 freetyrosine. The far-UV band of the spectra (<300 nm) has not been reported before. Theirmain initial photoproducts are p-alanylphenoxyl radical (λ_(max)=410,390nm) and an uniden-tified radical (λ_(max)=270 nm). The photolysis yields are closely correlative with the disso-ciation rate of hydroxyl group on phenol ring of tyrosine residues, which in turn dependson the exposed degree of these residues. The quantum yields of the phenoxyl radicals form-ed in photolysis of insulin and DPI were determined and compared with that of free tyro-sine. Based on the comparison, the number of light accessible tyrosine residue in insulin andDPI can be calculated, which provides more quantitative information on the exposed degreeof tyrosine residues in these two proteins.
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