Wiesehahn G, Hearst J E
Proc Natl Acad Sci U S A. 1978 Jun;75(6):2703-7. doi: 10.1073/pnas.75.6.2703.
Derivatives of furo[3,2-g]coumarin (psoralen) can bind to the DNA double helix and, in the presence of long-wavelength UV light, the bound psoralen may react covalently with pyrimidine residues on one or both strands of the helix. By using agarose gel electrophoresis, we have determined the unwinding angle associated with each of four different psoralen derivatives to be 28 degrees +/- 4 degrees . For 4,5',8-trimethylpsoralen (trioxsalen) the unwinding angle was found to be independent of the initial DNA superhelix density in the range that is accessible to agarose gel electrophoresis. Also by using agarose gel electrophoresis, we have determined the unwinding angle for ethidium intercalation. This was done by the total relaxation of supercoiled DNA in the presence of a series of ethidium concentrations. By using published values for the association constant for ethidium binding to DNA and evaluating the final superhelix density (after removal of ethidium) of the DNA on gels, we calculated an unwinding angle of 29 degrees +/- 3 degrees . Assuming an unwinding angle of 28 degrees for the noncovalent intercalation of psoralen derivatives, we used the same procedure to determine intercalation binding constants. The association constants for 4'-aminomethyltrioxsalen were 300-1400 M(-1) in NaCl at 0.2-0.05 M and 300-2500 M(-1) in Mg(2+) at 4-0.5 mM. The association constant for 4'-hydroxymethyltrioxsalen in 0.5 mM Mg(2+) was determined to be 70 M(-1).
呋喃并[3,2 - g]香豆素（补骨脂素）的衍生物能够与DNA双螺旋结合，并且在长波长紫外光存在的情况下，结合的补骨脂素可能会与螺旋单链或双链上的嘧啶残基发生共价反应。通过琼脂糖凝胶电泳，我们测定了四种不同补骨脂素衍生物各自对应的解旋角为28度±4度。对于4,5',8 - 三甲基补骨脂素（三甲沙林），发现在琼脂糖凝胶电泳可检测的范围内，解旋角与初始DNA超螺旋密度无关。同样通过琼脂糖凝胶电泳，我们测定了溴化乙锭嵌入的解旋角。这是通过在一系列溴化乙锭浓度下使超螺旋DNA完全松弛来完成的。利用已发表的溴化乙锭与DNA结合的缔合常数，并评估凝胶上DNA的最终超螺旋密度（去除溴化乙锭后），我们计算出解旋角为29度±3度。假设补骨脂素衍生物非共价嵌入的解旋角为28度，我们采用相同的程序来测定嵌入结合常数。在0.2 - 0.05 M的NaCl中，4'-氨甲基三甲沙林的缔合常数为300 - 1400 M⁻¹，在4 - 0.5 mM的Mg²⁺中为300 - 2500 M⁻¹。在0.5 mM的Mg²⁺中，4'-羟甲基三甲沙林的缔合常数测定为70 M⁻¹。
