DNA BINDING & BENDING BY INTEGRATION HOST FACTOR (IHF)

记录[Glu 1]-纤维蛋白肽离子的MS/MS谱 在O16和O18标记的水中辐解后产生， 未修饰的肽和用O16和O18修饰的肽。 这些 光谱显示，苯丙氨酸残基被O16修饰， 和O18，如y型离子y4的m/z值的偏移所示 至y11和N端b型离子b10至b13。 两 苯丙氨酸残基被部分修饰，如 不含O16/O18的y4和b10片段的存在， 修饰肽的光谱。 的质谱研究 其他肽在O18标记水中的辐解产物显示， 蛋氨酸与羟基自由基和氧反应， 苯丙氨酸和酪氨酸残基主要与羟基 根的 脯氨酸仅被分子氧氧化， +14和+16 U产物可能是通过自由基离子形成， 水合电子，然后与O2反应。 的损失 分子氢转化为酮，形成了+14 辐射分解产物。 色氨酸显示多重氧化形成 产品在+16和+32u。 半胱氨酸被证明可以结合多达 三个氧气 在O18-标记的水辐解表明，羟基 自由基和分子氧都在竞争形成这些 产品.

MS/MS spectra were recorded for the ions of [Glu1]-fibrinopeptide produced upon radiolysis in O16 and O18-labeled water that correspond to unmodified peptide, and peptide modified with O16 and O18. These spectra reveal that phenylalanine residues are modified with both O16 and O18 as indicated by the shift in m/z values for the y-type ions y4 through y11 and N-terminal b-type ions b10 through b13. Both phenylalanine residues are partially modified as indicated by the presence of the y4 and b10 fragments that do not contain O16/ O18 in spectra for modified peptide. Mass spectrometry studies of the radiolysis products of other peptides in O18-labeled water reveal that methionine reacts with hydroxyl radicals and oxygen while phenylalanine and tyrosine residues react predominantly with hydroxyl radicals. Proline is oxidized solely by molecular oxygen to produce +14 and +16u products presumably through radical ion formation by hydrated electrons, followed by reactions with O2. The loss of molecular hydrogen to a ketone accounts for the formation of the +14 radiolyzed product. Tryptophan shows multiple oxidation to form products at +16 and +32u. Cysteine is shown to incorporate up to three oxygens. Radiolysis in O18-labeled water revealed that hydroxyl radicals and molecular oxygen both compete in the formation of these products.