Plant Biotechnology Persa

en Kinetic Analysis of Guaiacol Peroxidase in Solanum lycopersicum under Immature and Post-Harvest Conditions in the Presence of Potential Amino Acid Inhibitors Plant physiology پژوهشي Research <div style="text-align: justify;">Objective: Tomato (Solanum lycopersicum), a climacteric fruit, is highly susceptible to oxidative degradation during ripening and postharvest storage, which compromises shelf life and visual quality. Guaiacol peroxidase (GPX), a key enzyme in oxidative processes, catalyzes the oxidation of phenolic compounds, contributing to enzymatic browning. This study aimed to characterize the kinetic properties and inhibition patterns of GPX across three physiological stages immature, ripe, and stored and to evaluate the modulatory effects of two natural amino acids, glycine and cysteine. Methods: GPX activity was quantified using spectrophotometric assays. Kinetic parameters (Km and Vmax) were determined via Michaelis–Menten and Lineweaver Burk analyses. Enzyme activity was assessed under varying substrate (guaiacol and hydrogen peroxide) concentrations and pH conditions to establish optimal catalytic parameters. Results: GPX activity was optimal at pH 6.5, with a consistent Km of 5 mM across all physiological stages. Vmax values increased progressively during ripening and storage (0.019, 0.027, and 0.033 µmol/min, respectively). Substrate inhibition occurred at guaiacol concentrations above 10 mM, with maximal activity observed at 10 mM hydrogen peroxide (100 µL). Both cysteine and glycine inhibited GPX, with cysteine showing greater potency across all stages, as reflected by 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 analysis 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: GPX activity in tomato is developmentally regulated and can be effectively suppressed by natural amino acids, particularly cysteine. These findings provide promising bio-based strategies to reduce enzymatic browning and enhance oxidative stability during postharvest handling of tomatoes. <img alt="" src="./files/site1/images/copuediting.png" style="width: 586px; height: 265px;" >  </div> ,Antioxidant,Free Radical,Inhibitor,Peroxidase,Glycine,Tomato 0 0 http://pbp.medilam.ac.ir/browse.php?a_code=A-10-1505-3&slc_lang=en&sid=1 shahriar saeidian saeedyan@pnu.ac.ir 10031947532846005945 10031947532846005945 Yes payame noor university zhila zarei zh.zarei@gmail.com 10031947532846005946 0009-0001-3802-9496 No MSc biochemistry, Biology Department, Payame Noor University