Dudkin S M, Karabashyan L V, Karpeisky M Y, Mikhailov S N, Padyukova N S, Sakharovsky V G
Biochem J. 1977 Dec 1;167(3):749-57. doi: 10.1042/bj1670749.
The circular-dichroism and proton-magnetic-resonance spectra of complexes of ribonuclease A with dihydrouridine 3'-phosphate, 2'- and 3'-CMP, arabinosyl-3'-CMP, 1-(2-hydroxyethyl)cytosine 2'-phosphate and 1-(3-hydroxypropyl)cytosine 3'-phosphate were studied. Comparison of the results shows that non-additivity of the circular-dichroic spectrum of an enzyme-nucleotide complex may be due to: (a), alteration of the circular dichroic spectrum of the nucleotide under the influence of the asymmetric protein matrix (induced dichroism), and (b) a change in the nucleotide conformation. The contribution of each of the two factors was estimated to calculate the circular-dichoroic spectra of 2'-CMP and 3'-CMP in complex with ribonuclease A. 3'-CMP in this complex was characterized by negative circular dichroism in the long-wavelength absorption band of the nucleotide, whereas 2'-CMP was characterized by positive circular dichroism. Since both nucleotides in the complex are known to be in an anti conformation, it follows that even small changes in the conformation considerably modify the circular-dichroic spectrum of the nucleotide in complex with the enzyme.
对核糖核酸酶A与二氢尿苷3'-磷酸、2'-和3'-胞苷酸、阿拉伯糖基-3'-胞苷酸、1-(2-羟乙基)胞嘧啶2'-磷酸以及1-(3-羟丙基)胞嘧啶3'-磷酸形成的复合物的圆二色光谱和质子磁共振光谱进行了研究。结果比较表明，酶-核苷酸复合物圆二色光谱的非加和性可能归因于：(a) 在不对称蛋白质基质的影响下核苷酸圆二色光谱的改变（诱导二色性），以及(b) 核苷酸构象的变化。对这两个因素各自的贡献进行了估算，以计算与核糖核酸酶A形成复合物的2'-胞苷酸和3'-胞苷酸的圆二色光谱。该复合物中的3'-胞苷酸在核苷酸的长波长吸收带中表现出负圆二色性，而2'-胞苷酸表现出正圆二色性。由于已知复合物中的两种核苷酸均处于反式构象，因此可以得出结论，即使构象的微小变化也会显著改变与酶形成复合物的核苷酸的圆二色光谱。
