(596aw) Interaction Between Coenzyme Q10 and Human Serum Albumin: Spectroscopic Approach

Coenzyme Q₁₀ (CoQ₁₀)
exists in all body cells, and it is vital to a series of activities related to
energy metabolism. Nowadays, CoQ₁₀ is widely consumed by humans
since it is well known as an important nutrient and a therapeutic agent in
supporting health and as an inhibitor of ageing. Moreover, CoQ₁₀
also has good effect in inhibiting the growth of human cancer cells. Human
serum albumin (HSA) is the most prominent protein within blood plasma, and it
plays an important role in the binding of many kinds of ligands, such as drugs.
Due to its significantly physiological functions, HSA has been widely used as a
model protein in evaluating protein¨Cdrug interactions.

So far, different spectroscopic approaches
have been broadly used to detect the binding of protein with various of drugs.
However, the interaction of CoQ₁₀ with HSA has not been explored.
Therefore, in this paper, UV-vis absorption, fluorescence and circular
dichroism (CD) spectroscopies were employed to reveal the mechanism of the
binding between coenzyme Q₁₀ (CoQ₁₀) and human serum
albumin (HSA) under physiological conditions (pH=7.4). The binding parameters
have been calculated by fluorescence quenching method. The results demonstrated
that the fluorescence quenching of HSA by CoQ₁₀ was mainly static quenching due to the
formation of HAS-CoQ₁₀ complex, and the number of binding sites (n)
equal to 1. The thermodynamic parameters (DH = - 43.18 kJ mol^-1,
DS = - 47.05 J mol^-1 K^-1, DG = - 29.15 kJ mol^-1)
indicated that the enthalpy-driven binding process was spontaneous,
and the main binding forces between CoQ₁₀ and HSA were hydrogen
bonds and Van der Waals forces. The competitive experiments using different
site markers indicated that subdomains IIA (site I) of HSA was the primary
binding site for CoQ₁₀. The average binding distance (r)
between HSA and CoQ₁₀ was 4.29 nm, which was estimated according to
the Forster's theory of non-radiation energy transfer. The CD spectra, UV-vis
absorption and synchronous fluorescence spectroscopy data showed the slight
conformational changes of HSA in the presence of CoQ₁₀.

This work was supported by the Program for
New Century Excellent Talents in Chinese University (NCET-08-0386), the 863
Program of China (2008AA10Z318), the Natural Science Foundation of China
(20976125; 31071509; 51173128) and Tianjin (10JCYBJC05100), and the Program of
Introducing Talents of Discipline to Universities of China (No. B06006).

Figure (A) Binding site of CoQ₁₀ in
the HSA, (B) Energy
transfer between HSA and CoQ₁₀, (C) CD spectra of HSA in the
presence of CoQ₁₀.