Table 2.

Summary of the parameters describing the allosteric binding of (+)-daunorubicin and (−)-daunorubicin (WP900) to [poly(dGdC)]₂ under ionic conditions favorable to either the Z- or B-DNA conformation

Parameter*	Daunorubicin† Z → B	WP900‡ B → Z
σ	0.001	0.01
s	0.635	0.92
K1	0.8 × 104	1.5 × 104
K2	3.5 × 105	7.8 × 104
K2/K1	44	5.2

^*The parameter, σ, is the nucleation parameter for the conversion of a base pair within a stretch of Z (or B) helix to the B (or Z) conformation; s is the equilibrium constant for the conversion of a base pair at a pre-existing B-Z interface from the Z (or B) to the B (or Z) conformation; and K₁ is the binding constant for the interaction of a drug molecule with an isolated site in the form-1 conformation; K₂ is the binding constant for the interaction of a drug molecule with an isolated site in the form-2 conformation. 

^† Daunorubicin binding to [poly(dGdC)]₂ in buffered 3.0 M NaCl solution. Titration experiments were carried out using the same conditions described in supplementary Table 3. In this case, K₁ refers to binding to the initial Z-form DNA, whereas K₂ refers to binding to the preferred B-form DNA. 

^‡ WP900 binding to [poly(dGdC)]₂ in buffered 2.1 M NaCl solution. Titration experiments were carried out using the same conditions described in supplementary Table 3. In this case, K₁ refers to binding to the initial B-form DNA, whereas K₂ refers to binding to the preferred Z-form DNA.