Studies on the interaction of total saponins of panax notoginseng and human serum albumin by Fourier transform infrared spectroscopy

Total saponins of panax notoginseng (TPNS), isolated from the roots of panax notoginseng (Burk) F.H. Chen, have been considered as the main active components of San-Chi and have various therapeutical actions. Their interactions with human serum albumin have been investigated by Fourier transformed infrared spectrometry and fluorescence methods. The results showed that TPNS combined with HSA through C=O and C-N groups of polypeptide chain. The drug-protein combination caused the significant loss of alpha-helix structure and the microenvironment changes of the tyrosine residues in protein at higher drug concentration. Combining the curve-fitting results of amide I and amide III bands, the alterations of protein secondary structure after drug complexation were quantitatively determined. The alpha-helix structure has a decrease of approximately 6%, from 55 to 49% and the beta-sheet increased approximately 3%, from 23 to 26% at high drug concentration. However, no major alterations were observed for the beta-turn and random coil structures up on drug-protein binding.