Study Of The Interaction Between Three Anthocyanins And Serum Albumins

Anthocyanin is an important kind of water-soluble pigment existing widely in plants, and hasvarious health benefits to the human body. The number and location of the hydroxyl groups ofthe parent nucleus of Anthocyanins have significant effects on their activities. This researchemployed different spectroscopic methods (i.e. fluorescence spectroscopy, UV-vis absorbanceand circular dichroism) to investigate the mutual interactions between threecommon anthocyanins in nature (Pelargonidin-3-O-glucoside, P3G; Cyanidin-3-O-glucoside,C3G and Delphinidin-3-O-glucoside, D3G) and human serum albumin (HSA) underphysiological pH conditions, to obtain the relevant information of the interaction and theinfluence of the number of B-ring hydroxyl on the binding affinity for HSA. Meanwhile,interaction between delphinidin-3-O-glucoside and bovine serum albumin (BSA) wasinvestigated by multispectroscopic methods and molecular modeling. In addition, the effects ofpH and metal ions on the binding constants were discussed. Moreover, the effects of the bindingto HSA on the antioxidant capacity of the three anthocyanins were studied by DPPH method,which provided the theory basis for the evaluation of the antioxidant capacity of anthocyanins.This paper mainly consists of four parts, as follows:1. In the chapter one, the structure, classification and physiological function of anthocyaninswere summarized as well as the structure and function of serum albumin. The commonly usedspectroscopic methods and advances in the research of the interaction between anthocyanins andserum albumin were also introduced.2. In the chapter two, different spectroscopic methods were employed to investigate theinteractions between three differently substituted B-ring hydroxyl groups (P3G, C3G and D3G)and HSA under simulate physiological pH conditions. The results showed that P3G, C3G andD3G could result in quenching of the intrinsic fluorescence. The quenching belonged to staticfluorescence type, with a non-radiation energy transfer, and the quenching of D3G also containeddynamic quenching. The distances between HSA and P3G/C3G/D3G were obtained as2.83nm,2.58nm and2.34nm, respectively. The comparison result of the strength of comprehensive binding parameter Y was YD3G> YC3G> YP3G,which indicated that the order of the bindingstrength among the three anthocyanins was D3G> C3G> P3G. Results of site markercompetitive experiments showed that the three anthocyanins mainly bound to HSA in site I.Moreover, the secondary structure of HSA was changed in the presence of P3G/C3G/D3G. The-helix percentage of P3G-HSA increased while that of C3G/D3G-HSA decreased. Overall,these results showed that the number of B-ring-OH in each molecule played an important role inthe interaction of these anthocyanins with HSA.3. In the chapter three, the interaction between D3G and BSA was investigated bymultispectroscopic methods and molecular modeling. D3G effectively quenched the intrinsicfluorescence of BSA via static quenching. The hydrogen bonds and van der Waals forces playedmajor roles in stabilizing the D3G-BSA complex. In addition, the effects of pH and metal ions onthe binding constants were discussed. In addition, the secondary structure of the BSA waschanged by the addition of D3G and the-helix content of BSA decreased. Furthermore, thestudy of site marker competitive experiments and molecular modeling indicated that D3G couldbind to site I of BSA.4. In the chapter four, the effects of the binding to HSA on the antioxidant capacity of the threeanthocyanins were studied by DPPH method. The three anthocyanins showed great antioxidantability, which increased with the increase of B ring hydroxyl number. After the combination withHSA, the DPPH radical scavenging capacity of anthocyanins obviously decreased. Furthermore,the influence on the antioxidant activity increased with the increasing affinities of BSA-anthocyanins complexes.