Figure 7.

Ni²⁺ and L-cys binding to coptisine (Cop) measured using UV-visible spectroscopy. 16 μM Cop in the absence or presence of different molar equivalents of Ni²⁺ (1 mM NiCl₂) (A) or L-cys (1 mM) (B) in 20 mM HEPES buffer, pH 7.5. A-F, 0.0 to 320 μM of Ni²⁺; A-F, 0.0 to 200 μM of L-cys. The inset shows the titration curves for binding of Ni²⁺ or L-cys to Cop at 355 nm. Wavelength (nm) is represented on the x-axis and absorption (Abs) is represented on the y-axis.