Sjöberg B M, Reichard P, Gräslund A, Ehrenberg A
J Biol Chem. 1978 Oct 10;253(19):6863-5.
One of the two nonidentical subunits of ribonucleotide reductase from Escherichia coli, protein B2, contains an organic free radical required for enzyme activity. Earlier isotope subtitution experiments (Sjöberg, B.-M., Reichard, P. Gräslund, A., and Ehrenberg, A. (1977) J. Biol. Chem. 252, 536-541) demonstrated that the radical was localized to a tyrosine residue of the enzyme and suggested that the spin density of the radical was centered at the methylene carbon of tyrosine. However, additional isotope substitution experiments now show that the spin density of the radical must be delocalized over the aromatic ring of the tyrosine residue.
来自大肠杆菌的核糖核苷酸还原酶的两个不同亚基之一，即蛋白质B2，含有酶活性所需的有机自由基。早期的同位素取代实验（舍贝里，B.-M.，赖夏德，P.，格拉斯隆德，A.，和埃伦贝里，A.（1977年）《生物化学杂志》252卷，536 - 541页）表明该自由基定位于酶的一个酪氨酸残基上，并表明该自由基的自旋密度集中在酪氨酸的亚甲基碳上。然而，现在额外的同位素取代实验表明，该自由基的自旋密度必须离域在酪氨酸残基的芳香环上。
