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saeidian S, zarei Z. Kinetic Analysis of Guaiacol Peroxidase in Solanum lycopersicum under Immature and Post-Harvest Conditions in the Presence of Potential Amino Acid Inhibitors. pbp 2025; 7 (In press)
URL: http://pbp.medilam.ac.ir/article-1-324-en.html
URL: http://pbp.medilam.ac.ir/article-1-324-en.html
1- payame noor university , saeedyan@pnu.ac.ir
2- MSc biochemistry, Biology Department, Payame Noor University
2- MSc biochemistry, Biology Department, Payame Noor University
Abstract: (98 Views)
Objective:Tomato (Solanum lycopersicum) is a climacteric fruit highly susceptible to oxidative degradation during ripening and storage, which limits its postharvest longevity and visual quality. One of the key enzymes involved in these oxidative processes is guaiacol peroxidase, which catalyzes the oxidation of phenolic compounds and contributes to enzymatic browning.
Objective: The objective of this study was to investigate the kinetic behavior and inhibition patterns of guaiacol peroxidase in tomato fruit across three physiological stages—immature, ripe, and stored—while assessing the modulatory effects of two natural amino acids, glycine and cysteine.
Methods: Peroxidase activity was measured using spectrophotometric assays, and kinetic parameters (Km, Vmax) were calculated using Michaelis-Menten and Lineweaver-Burk models. Enzyme behavior was analyzed under variable substrate concentrations (guaiacol and hydrogen peroxide) and pH conditions to determine optimal operating parameters.
Results: The results showed that peroxidase exhibited peak activity at pH 6.5 and a consistent Km of 5 mM across all stages, while Vmax increased progressively during ripening and storage (0.52 → 0.72 → 0.87 absorbance/min). Substrate inhibition was evident at guaiacol concentrations above 10 mM, and the addition of 10 mM hydrogen peroxide (100 µL) yielded maximal enzymatic response. Inhibitor assays revealed that cysteine had a stronger inhibitory effect than glycine at all stages, with lower IC50 values: 0.8 vs. 1.0 mM (immature), 0.9 vs. 1.3 mM (ripe), and 1.2 vs. 1.5 mM (stored). Lineweaver-Burk plots indicated non-competitive inhibition in immature fruit, shifting to competitive inhibition in ripe and stored stages—suggesting developmental changes in enzyme structure or isoform composition.
Conclusion: In conclusion, the study demonstrates that peroxidase activity in tomato is developmentally regulated and can be effectively suppressed by natural amino acids, particularly cysteine. These findings offer promising strategies for reducing enzymatic browning and enhancing oxidative stability in postharvest tomato handling through bio-based interventions.
Objective: The objective of this study was to investigate the kinetic behavior and inhibition patterns of guaiacol peroxidase in tomato fruit across three physiological stages—immature, ripe, and stored—while assessing the modulatory effects of two natural amino acids, glycine and cysteine.
Methods: Peroxidase activity was measured using spectrophotometric assays, and kinetic parameters (Km, Vmax) were calculated using Michaelis-Menten and Lineweaver-Burk models. Enzyme behavior was analyzed under variable substrate concentrations (guaiacol and hydrogen peroxide) and pH conditions to determine optimal operating parameters.
Results: The results showed that peroxidase exhibited peak activity at pH 6.5 and a consistent Km of 5 mM across all stages, while Vmax increased progressively during ripening and storage (0.52 → 0.72 → 0.87 absorbance/min). Substrate inhibition was evident at guaiacol concentrations above 10 mM, and the addition of 10 mM hydrogen peroxide (100 µL) yielded maximal enzymatic response. Inhibitor assays revealed that cysteine had a stronger inhibitory effect than glycine at all stages, with lower IC50 values: 0.8 vs. 1.0 mM (immature), 0.9 vs. 1.3 mM (ripe), and 1.2 vs. 1.5 mM (stored). Lineweaver-Burk plots indicated non-competitive inhibition in immature fruit, shifting to competitive inhibition in ripe and stored stages—suggesting developmental changes in enzyme structure or isoform composition.
Conclusion: In conclusion, the study demonstrates that peroxidase activity in tomato is developmentally regulated and can be effectively suppressed by natural amino acids, particularly cysteine. These findings offer promising strategies for reducing enzymatic browning and enhancing oxidative stability in postharvest tomato handling through bio-based interventions.
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