Fox K R, Olsen R K, Waring M J
Biochim Biophys Acta. 1982 Mar 29;696(3):315-22. doi: 10.1016/0167-4781(82)90063-x.
The interaction between TANDEM (a des-methyl analogue of triostin A) and poly(dA-dT) results in extension of the helix by 6.8 A for each ligand molecule bound, exactly as predicted for a bis-intercalation reaction. Cooperativity is evident in Scatchard plots for the interaction at ionic strengths of 0.2 and 1.0, where the binding constant is diminished compared to that which pertains at low salt concentrations. Binding to a natural DNA (calf thymus), already considerably weaker than binding to poly(dA-dT), is also sensitive to increased ionic strength. With a self-complementary octanucleotide d(G-G-T-A-T-A-C-C) the binding curve indicates the presence of a single des-N-tetramethyltriostin A binding site per helical fragment with a non-cooperative association constant about 6 . 10(6) M-1. Detergent-induced dissociation of des-N-tetramethyltriostin A-poly(dA-dT) complexes results in a simple exponential decay at all levels of binding, but the time constant of decay is dependent upon the initial binding ratio. This behavior cannot directly explain the cooperativity of equilibrium binding isotherms but suggests the occurrence of relatively long-lived perturbations of the helical structure by binding of the ligand. [Ala3, Ala7]des-N-tetramethyltriostin A, which has a more flexible octapeptide ring lacking the disulphide cross-bridge, dissociates from poly(dA-dT) much faster than des-N-tetramethyltriostin A. Dissociation of des-N-tetramethyltriostin A from calf thymus DNA is more rapid than dissociation of triostin A or other quinoxaline antibiotics, which may account for its low antimicrobial activity.
串联菌素（曲古抑菌素A的去甲基类似物）与聚（dA-dT）之间的相互作用导致每结合一个配体分子，螺旋延长6.8埃，这与双插入反应的预测完全一致。在离子强度为0.2和1.0时的相互作用的斯卡查德图中，协同性很明显，与低盐浓度下的结合常数相比，此时的结合常数减小。与天然DNA（小牛胸腺DNA）的结合，其强度已经比与聚（dA-dT）的结合弱得多，对离子强度的增加也很敏感。对于自互补八聚体d（G-G-T-A-T-A-C-C），结合曲线表明每个螺旋片段存在一个单一的去N-四甲基曲古抑菌素A结合位点，其非协同缔合常数约为6×10⁶ M⁻¹。去污剂诱导的去N-四甲基曲古抑菌素A-聚（dA-dT）复合物的解离在所有结合水平上都导致简单的指数衰减，但衰减的时间常数取决于初始结合比。这种行为不能直接解释平衡结合等温线的协同性，但表明配体结合会导致螺旋结构发生相对持久的扰动。[Ala3, Ala7]去N-四甲基曲古抑菌素A，其八肽环更灵活，没有二硫键交联桥，从聚（dA-dT）上解离的速度比去N-四甲基曲古抑菌素A快得多。去N-四甲基曲古抑菌素A从小牛胸腺DNA上的解离比曲古抑菌素A或其他喹喔啉类抗生素的解离更快，这可能解释了它抗菌活性较低的原因。
