The mechanism study in the interactions of sorghum procyanidins trimer with porcine pancreatic α-amylase

To examine the mechanisms in the interaction of sorghum procyanidins trimer (SPT) with porcine pancreatic α-amylase (PPA), fluorescence quenching, circular dichroism, and UV spectra methods were adopted. The procyanidins binding mode, binding constant and effect of procyanidins on protein stability and conformation were determined. The fluorescence spectroscopy results showed that the Stern–Volmer quenching constant KSV of SPT on PPA, bimolecular quenching constant kq, and apparent static quenching constant K were 2639.5 M−1, 2.6395 × 1011 M−1 s−1, and 495.19 M−1, respectively. In addition, binding constant KA and number of binding sites were 872.971 M−1 and 1, respectively. Circular dichroism study revealed that PPA conformation was altered by SPT with a major reduction of β-sheet, increase of β-turn, minor change of random coil. UV spectra indicated that SPT influenced the micro-environment of aromatic amino acid residues in PPA. These findings directly elucidate the mechanisms of high molecular weight SPT in interaction with PPA.