Abstract: This study evaluated the conformational changes of polyphenol oxidase (PPO) in the crystalline solid (C-) and liquid (L-) states at room temperature (298.15 K) and normal or ultra-high pressure (0.1-400.0 MPa). The results indicated that when the pressure increased from 0.1 to 400.0 MPa, the spatial structure of PPO in both states became unstable. Compared with L-PPO, C-PPO was more susceptible to pressure, and exhibited higher residue fluctuations, reduced solvent accessible surface area and volume and a denser structure. With the transition of α-helices to random coils under high pressure conditions, the number of hydrogen bonds became unstable and α-helix elasticity decreased, thus leading to significant conformational differences. The active site of the Cu2+ position was displaced, the inter-residue distance was altered and random motion appeared, thereby interfering with substrate binding. In conclusion, both physical state and pressure level can influence PPO’s spatial structure, residue mobility, and substrate binding range, ultimately impacting the enzyme’s stability, and their impacts on the degree of enzyme denaturation can be ranked as follows: solid state > liquid state, and physical state > pressure level.

Key words: polyphenol oxidase; molecular dynamics simulation; physical state; ultra-high pressure; stability