Polymorphic Nucleic Acid Binding of Bioactive Isoquinoline Alkaloids and Their Role in Cancer

Table 2

Comparative binding parameters of interaction of various alkaloids with calf thymus DNA and covalently closed superhelical DNA.

Alkaloid	𝐾^a (×10^5 M^−1)	𝑛	Δ𝑇m^b(°C)	𝛽^c	𝜃^d	References
Berberine	0.38	4.0	7.0	1.35	12.6	[28, 30]
					13.0
Palmatine	0.19	4.0	11.0	1.40	15.0	[28, 31]
Coralyne	1.0	9.0	12.0	1.62	21.0	[28, 32]
					18.0
Sanguinarine	9.45	3.4	21.3	1.86	27.0	[33, 34]

^a𝐾 the intrinsic binding constant determined using equation 𝑟/𝐶_f=𝐾(1−𝑛𝑟)[(1−𝑛𝑟)/(1−(𝑛−1)𝑟)]^𝑛−1, where 𝑟 is the number of alkaloid molecules bound per mole of nucleotide and 𝐶_f is the molar concentration of free alkaloid, where 𝑛 denotes the binding site size in base pairs.
^bΔ𝑇_𝑚 is the 𝑇_𝑚 of the DNA in the presence of alkaloid-𝑇_𝑚 of the free DNA.
^c𝛽 value was calculated from the slope, when 𝐿/𝐿_𝑜 or (𝜂/𝜂₀)^1/3 is plotted against 𝑟 using the equation 𝐿/𝐿_𝑜=(𝜂/𝜂₀)^1/3=1+𝛽𝑟, where 𝐿 and 𝐿_𝑜 are the contour length of helix in presence and absence of ligand corresponding values of intrinsic viscosity (approximated to the reduced viscosity) of the solution and 𝑟 is the mole ligand bound /mole nucleotides.
^dunwinding angle.