Strzelczak G, Bobrowski K, Holcman J
Institute of Nuclear Chemistry and Technology, Warsaw, Poland.
Radiat Res. 1998 Dec;150(6):688-94.
Bimolecular rate constants for the reaction of the hydrated electron with zwitterionic forms of several linear oligopeptides containing methionine were determined using the pulse radiolysis technique. The rate constants were found to vary in the range of (0.2-1.2) x 10(9) M(-1) s(-1). The reactivity of the peptides toward e(aq)- is governed by the pKa of the N-terminal amino group and the number of peptide bonds. At a fixed number of peptide bonds, the reactivity increases with the pKa, and for a given N-terminal amino acid residue, it increases with the number of peptide bonds. For the linear peptides the observed transient spectra are assigned to deaminated oligopeptide radicals, *CHRCONH approximately, obtained due to rapid deamination of the corresponding electron adducts formed initially. The radicals derived from oligopeptides containing methionine at the N-terminus absorb at approximately 400 nm with extinction coefficients of approximately 1300+/-150 M(-1) cm(-1). Their absorption maxima are shifted hypsochromically by approximately 30 nm with respect to those derived from oligopeptides with glycine at the N-terminus. The e(aq)- reacts with cyclic Met-Met, k = 2.0 x 10(9) M(-1) s(-1), probably by addition to the carbonyl bond, forming an adduct absorbing below 250 nm with epsilon250 = 2300+/-250 M(-1) cm(-1).
使用脉冲辐解技术测定了水合电子与几种含蛋氨酸的线性寡肽两性离子形式反应的双分子速率常数。发现速率常数在(0.2 - 1.2)×10⁹ M⁻¹ s⁻¹范围内变化。肽对水合电子e(aq)⁻的反应活性受N端氨基的pKa和肽键数量的控制。在肽键数量固定时，反应活性随pKa增加，对于给定的N端氨基酸残基，反应活性随肽键数量增加。对于线性肽，观察到的瞬态光谱归属于脱氨基寡肽自由基*CHRCONH approximately，它是由最初形成的相应电子加合物快速脱氨基产生的。N端含蛋氨酸的寡肽衍生的自由基在约400 nm处有吸收，消光系数约为1300±150 M⁻¹ cm⁻¹。相对于N端含甘氨酸的寡肽衍生的自由基，它们的吸收最大值发生了约30 nm的紫移。水合电子e(aq)⁻与环式Met - Met反应，k = 2.0×10⁹ M⁻¹ s⁻¹，可能是通过加成到羰基键上，形成一个在250 nm以下有吸收的加合物，ε250 = 2300±250 M⁻¹ cm⁻¹。
