Structure analysis and inhibition mechanism of peroxidase in 'Zhongshu 1' sweet potato.

• Peroxidases produce o -quinones and form black or brown deleterious pigments. • Structure and catalytic sites of peroxidase from 'Zhongshu 1′ sweet potato were resolved. • Ascorbic acid, sodium metabisulfite, glutathione inhibited browning of sweet potato. • Mechanism and type between peroxidase and inhibitors were revealed by molecular docking. Browning is an obstacle in industrial development of sweet potato. Peroxidase from sweet potato cv. 'Zhongshu 1′ was purified and analyzed by chromatography and mass spectrometry. Peroxidase from 'Zhongshu 1′ sweet potato was a monomeric protein with 37.2 kDa. A binding site of peroxidase to guaiacol was discovered using molecular docking, with Arg61 and Ala191 being near the active region important for guaiacol catalysis. The IC 50 values of ascorbic acid, sodium metabisulfite and glutathione were (1.97 ± 0.03)×10−4, (2.99 ± 0.07)×10−4 and (6.87 ± 0.12)×10-3 mol L-1, respectively. These compounds were competitive (ascorbic acid, (1.96 ± 0.03) ×10−4 mol L-1), non-competitive (sodium metabisulfite, (1.08 ± 0.03) ×10−4 mol L-1) and uncompetitive inhibitors (glutathione, (10.78 ± 0.05)×10-3 mol L-1) of peroxidase. Fluorescence spectrum showed the static quenching type of three inhibitors. The change of residues near the active site in peroxidase contributed to prevention of browning. [ABSTRACT FROM AUTHOR]