Plum G E, Bloomfield V A
Department of Biochemistry, University of Minnesota, St. Paul 55108.
Biopolymers. 1990 Jan;29(1):13-27. doi: 10.1002/bip.360290105.
We have measured the thermal melting profile for poly[d(AT)].poly[d(TA)] as a function of concentration of three trivalent cations: spermidine, me8spermidine, and hexammine cobalt(III). Using McGhee's (1976) theory of DNA melting in the presence of ligands, we have estimated association constants Kh, Kc and binding site sizes nh, nc for binding to double-helical (h) and single-stranded (c) polynucleotide. The results are as follows: (table; see text) The binding parameters for spermidine and hexammine cobalt(III) to double helical molecules agree fairly well with direct equilibrium dialysis measurements, and are in reasonable accord with predictions of counterion condensation theory. However, despite their identical charges, the three ligands bind to single-stranded DNA with quite different affinities. Estimates of the charge spacing of single-stranded DNA suggest that poly[d(AT)] is less elongated in the presence of spermidine and hexammine cobalt(III) than it is when complexed with me8spermidine.
我们测量了聚[d(AT)].聚[d(TA)]的热解链曲线，该曲线是三种三价阳离子（亚精胺、甲基化亚精胺和六氨合钴(III)）浓度的函数。利用麦吉（1976年）在配体存在下DNA解链的理论，我们估算了与双螺旋（h）和单链（c）多核苷酸结合的缔合常数Kh、Kc以及结合位点大小nh、nc。结果如下：（表格；见正文）亚精胺和六氨合钴(III)与双螺旋分子的结合参数与直接平衡透析测量结果相当吻合，并且与反离子凝聚理论的预测合理一致。然而，尽管这三种配体电荷相同，但它们与单链DNA的结合亲和力却大不相同。单链DNA电荷间距的估算表明，与甲基化亚精胺复合时相比，在亚精胺和六氨合钴(III)存在下，聚[d(AT)]的伸展程度较小。
