Chemical modification of stem bromelain with anhydride groups to enhance its stability and catalytic activity

Chemical modification of lysine residues in stem bromelain was carried out using two novel reagents pyromellitic anhydride acid and poly(maleic anhydride). About 60% and 57% of the residues in bromelain were found to be modified by pyromellitic anhydride and poly(maleic anhydride), respectively. The modification brought about enhancement of thermal stability and the resistance to alkali and the surfactant. The optimum pH shifted from 7 to 9. Thermodynamic parameters, ΔH*, ΔG* and ΔS*, were determined as a function of temperature. The kinetic constants Km of the modified enzymes were determined as 0.4092 × 10−2 and 0.2825 × 10−2 mol l−1, respectively. SDS-PAGE profiling revealed a major bands of native and modified enzyme with molecular weights of 26 and 28.5 kDa. The results of FT-IR studies suggested that the modification caused only local structural changes. These results provide guidance for future development of stable protein formulations.