Purification and comparative characterization of monophenolase and diphenolase activities from a wild edible mushroom (Macrolepiota gracilenta)

Affinity gel synthesis from the p-aminobenzoic acid derivative 4-amino-2-methylbenzoic acid and purification of polyphenol oxidase from various plant sources

The polyphenol oxidase (PPO) enzyme, which causes enzymatic browning, has been repeatedly purified from fruit and vegetables by affinity chromatography. In the present research, Sepharose 4B-l-tyrosine-4-amino-2-methylbenzoic acid, a novel affinity gel for the purification of the PPO enzyme with high efficiency, was synthesized. Additionally, Sepharose 4B-l-tyrosine-p-aminobenzoic acid affinity gel, known in the literature, was also synthesized, and 9.02, 16.57, and 28.13 purification folds were obtained for the PPO enzymes of potato, mushroom, and eggplant by the reference gel. The PPO enzymes of potato, mushroom, and eggplant were purified 41.17, 64.47, and 56.78-fold from the new 4-amino-2-methylbenzoic acid gel. Following their isolation from the new affinity column, the assessment of PPO enzyme purity involved the utilization of SDS-PAGE. According to the results from SDS-PAGE and native PAGE, the molecular weight of each enzyme was 50 kDa. Then, the inhibition effects of naringin, morin hydrate, esculin hydrate, homovanillic acid, vanillic acid, phloridzin dihydrate, and p-coumaric acid phenolic compounds on purified potato, mushroom, and eggplant PPO enzyme were investigated. Among the tested phenolic compounds, morin hydrate was determined to be the most potent inhibitor on the potato (Ki: 0.07 ± 0.03 μM), mushroom (Ki: 0.7 ± 0.3 μM), and eggplant (Ki: 4.8 ± 1.2 μM) PPO enzymes. The studies found that the weakest inhibitor was homovanillic acid for the potato (Ki: 1112 ± 324 μM), mushroom (Ki: 567 ± 81 μM), and eggplant (Ki: 2016.7 ± 805.6 μM) PPO enzymes. Kinetic assays indicated that morin hydrate was a remarkable inhibitor on PPO.

Purification and Properties of Polyphenol Oxidase of Dried Volvariella bombycina

Polyphenol oxidase (PPO) was purified and characterized from a dried wild edible and medicinal mushroom (V. bombycina). Using Sepharose 4B-L-tyrosine-p-aminobenzoic acid affinity chromatography, PPO was purified from the dried V. bombycina. The purification was completed with a 33.85-fold purification. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the purified enzyme migrated as a single band. The molecular weight of the purified enzyme was estimated by SDS-PAGE to be about 25 kDa. Catechol, 4-methyl catechol, and pyrogallol were used as substrates to determine the enzyme activity and its kinetic parameters (Km and Vmax). At the optimum pH and temperature, dried V. bombycina PPO's Km and Vmax values for catechol, 4-methyl catechol, and pyrogallol were found to be 1.67 mM-833.33 U/mL, 3.17 mM-158.73 U/mL, and 2.67 mM-3333.33 U/mL, respectively. Also investigated were the effects of pH and temperature on the enzymatic properties of PPO in dried V. bombycina. The optimum pH and temperature values for dried V. bombycina PPO obtained by using catechol, 4-methyl catechol, and pyrogallol as substrates were 6.5, 15 °C; 9.0, 20 °C; and 8.0, 15°C, respectively. This is the first study on the purification and characterization of PPO from dried V. bombycina.

Some indazoles as alternative inhibitors for potato polyphenol oxidase

Fresh-cut vegetables and fruits have gained attention among consumers because of their fresh appearance, lack of pollution, nutrition, and convenience. However, in fresh-cut foods, enzymatic browning is the main problem. Polyphenol oxidase (PPO) is a vital enzyme involved in the process of enzymatic browning. In this study, PPO was purified from potato using Sepharose 4B-l-tyrosine-p-aminobenzoic acid affinity chromatography and the effect of some indazoles on the enzyme was determined. The enzyme was purified with a specific activity of 52,857.14 EU/mg protein and 21.26-purification fold. Indazoles exhibited inhibitor properties for PPO with IC₅₀ values in the range of 0.11-1.12 mM and K_i values in the range of 0.15 ± 0.04-3.55 ± 0.88 mM. Among these compounds, 7-chloro-1H-indazole was shown as the most potent PPO inhibitor (K_i : 0.15 ± 0.04 mM). Determination of the enzyme's inhibition kinetics will simplify the testing of candidate PPO inhibitors.

A novel method for explaining the product inhibition mechanisms via molecular docking: inhibition studies for tyrosinase from Agaricus bisporus

The present study aims to investigate the substrate (4-methyl catechol and catechol) specificity and inhibition mechanisms (l-ascorbic acid, citric acid, and l-cysteine) of the tyrosinase enzyme (TYR), which is held responsible for browning in foods and hyperpigmentation in the human skin, through kinetic and molecular docking studies. During the experimental studies, the diphenolase activities of TYR were determined, following which the inhibitory effects of the inhibitors upon the diphenolase activities of TYR. The inhibition types were determined as competitively for l-ascorbic acid and citric acid and noncompetitive for l-cysteine. The kinetic results showed that the substrate specificity was better for catechol while l-cysteine showed the best inhibition profile. As for the in silico studies, they also showed that catechol had a better affinity in line with the experimental results of this study, considering the interactions of the substrates with TYR's active site residues and their distance to CuB metal ion, which is an indicator of diphenolase activity. Besides, the inhibitory mechanisms of the inhibitor molecules were explained by the molecular modeling studies, considering the binding number of the inhibitors with the active site amino acid residues of TYR, the number and length of H bonds, negative binding energy values, and their distance to CuB metal ion. Based on our results, we suggest that the novel method used in this study to explain the inhibitory mechanism of l-cysteine may provide an affordable alternative to the expensive methods available for explaining the inhibitory mechanism of TYR and those of other enzymes. HighlightsThe best affinity for the tyrosinase enzyme occurred with catechol.l-Ascorbic acid, citric acid, l-cysteine inhibited the diphenolic activity of tyrosinase.In silico studies confirmed the best affinity shown by catechol.Product inhibition mechanism of l-cysteine explained by in silico for the first time.Communicated by Ramaswamy H. Sarma.

Purification and biochemical characterization of polyphenol oxidase extracted from Kirmizi Kismis grape (Vitis vinifera L.)

The purification of the polyphenol oxidase (PPO) enzyme from Kirmizi Kismis grape (Vitis vinifera L.) was performed 61.23 times using affinity chromatography. The molecular weight of the enzyme was found to be about 38.1 kDa by SDS-PAGE as a single band. The optimum pH and temperature values were revealed to be 5.0 and 30°C, respectively, in the presence of 4-methyl catechol substrate. The thermal stability of PPO was examined and it was observed to maintain its activity at 20°C for 1 hr. K_m and V_max values were determined to be 4.8 mM and 2000,0 EU/ml for 4-methyl catechol as a substrate. IC₅₀ and K_i values and inhibition types were found for various browning agents and ascorbic acid had the strongest inhibitory impact on PPO. The inhibitory impact of Na⁺ , K⁺ , Mg²⁺ , Cu²⁺ , and Al³⁺ metal ions on the enzyme activity at final concentrations of 1 mM and 10 mM was examined. PRACTICAL APPLICATIONS: Grapes grown and processed take a significant place in our life. The grape has antioxidant, anticarcinogenic, antidiabetic and protective properties against bacteria and viruses. Furthermore, it takes an important position in the country's economy and social life due to providing raw materials to the food industry and having high export potential. Polyphenol oxidase, which is the leading actor of enzymatic browning reactions causing serious economic losses every year, was purified and characterized from Kirmizi Kismis grape (Vitis vinifera L.). This ancient grape variety has industrial processing and export potential due to its long storage life and resistance to oxidation. Therefore, the purification and biochemical characterization of polyphenol oxidase from Kirmizi Kismis grape are of great importance.

Partial Purification and Characterization of Polyphenol Oxidase from the Wild Edible Mushroom Lepiota Procera Using Three-Phase Partitioning

Polyphenol oxidase (PPO) from the wild edible mushroom Lepiota procera is partially purified and biochemically characterized using three-phase partitioning (TPP), which is an easily applied and effective method. This method includes ammonium sulfate saturation at different concentrations, t-butanol addition (1:1; 1:5), and adjustment of pH. Optimum purification parameters with 20% ammonium sulfate saturation and 1:1 t-butanol conditions led to the highest activity at bottom phase with 8.4 fold purification. Sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed the molecular weight of the purified enzyme to be 35 kDa. The partially purified PPO presented a high level of activity with L-DOPA (Michaelis-Menten constant, Km – 0.12 mM), followed by caffeic acid (0.27 mM) and 4-methylcatechol (0.46 mM) and it is classified as a catecholase type of PPO. The enzyme had peak activity at a temperature of 40 °C and a pH value of 7.0. These results demonstrate a new enzyme source and easy purification method, useful for various industrial applications.

Kinetic characterization of substrate-analogous inhibitors of tyrosinase

The development of effective tyrosinase inhibitors has become increasingly important in the cosmetic, medicinal, and agricultural industries for application as antibrowning and depigmenting agents. The kinetic mechanisms of action of tyrosinase on monophenols and o-diphenols are complex, particularly in the case of monophenols because of the lag period that occurs at the beginning of the reaction. When enzyme inhibitors are studied, the problem becomes more complicated because the lag period increases, which has led to erroneous identification of the type of inhibition that many compounds exert on the monophenolase activity and the inaccurate determination of their inhibition constants. When the degrees of inhibition of an inhibitor which is analogous to tyrosinase substrates are the same for both monophenolase and diphenolase activities, this means that the inhibitor binds to the same enzymatic species and so the inhibition constants should be similar for both activities. In this study, we demonstrate this typical behavior of substrate-analogous inhibitors and propose a methodology for determining the type of inhibition and the inhibition constants for the monophenolase and diphenolase activities of the enzyme. Benzoic acid and cinnamic acid were used as inhibitors and the monophenol/o-diphenol pairs l-tyrosine/l-dopa and α-methyl-L-tyrosine/α-methyl-L-dopa as substrates.