Interaction between Z-ligustilide from Radix Angelica sinensis and human serum albumin

Z-ligustilide (LIG), an essential oil extract from Radix Angelica sinensis, has broad pharmaceutical applications in treating cardiovascular and cerebrovascular diseases. Interaction of LIG with the major transport protein of human blood circulation, human serum albumin (HSA) has been investigated by steady-state, UV-vis and circular dichroism (CD) spectroscopic methods, as well as the effect of metal ions (e.g. Zn2+, Cu2+, Fe3+, Co2+, Ni2+) on the LIG-HSA system. Fluorescence results revealed that a moderate binding affinity (1.59 × 104 M−1 at 298 K) between LIG and HSA with a 1:1 stoichiometry. Thermodynamic analysis of the binding data (ΔS = +12.96 J mol−1 K−1 and ΔH = −20.11 kJ mol−1) suggested the involvement of hydrophobic and van der Waals forces, as well as hydrogen bonding in the complex formation. The specific binding distance r (3.75 nm) between donor (Trp-214) and acceptor (LIG) was obtained according to fluorescence resonance energy transfer. CD results showed that slight conformational changes occurred in the protein upon complexation with LIG.