Studies on interactions of pentagalloyl glucose, ellagic acid and gallic acid with bovine serum albumin: A spectroscopic analysis

Fluorescence techniques and circular dichroism (CD) were utilized to investigate the interactions of a typical gallotannin 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) and two simple phenolic compounds ellagic acid (EA) and gallic acid (GA) with bovine serum albumin (BSA). Fluorescence experiments showed that PGG and EA could strongly interact with BSA. The binding constants showed a pH-dependent binding of phenolic acids by BSA. The CD spectra revealed that GA, EA and PGG has slight effect on the secondary structure of BSA at the low concentration (50 μM). However, obvious alterations of the secondary structure of BSA were observed at high concentrations (from 100 μM to 500 μM). The interaction of GA, EA and PGG at high concentrations with BSA caused an unfolding of the secondary structure of BSA. PGG has a greater impact on the secondary structure of BSA when compared with small molecule compounds GA and EA.