Some indazoles as alternative inhibitors for potato polyphenol oxidase

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.

Development of a new affinity chromatography method for purification of horseradish peroxidase enzyme

In this study, benzohydroxamic acid molecules were synthesized from methyl 4-amino-2-methoxy, methyl 4-amino-3-nitro, methyl 4-amino-3-methyl, and methyl 4-amino-3-chloro benzoate molecules, and the horseradish peroxidase (HRP) enzyme was purified in one step using the affinity chromatography technique for the first time. The IC50 and Ki values for the 4-amino 3-methyl benzohydroxamic acid molecule were 0.136 and 0.132 ± 0.054 μM, respectively, while the IC50 and Ki values for the 4-amino-3-nitro benzohydroxamic acid molecule were 56.00 and 51.90 ± 9.90 μM, respectively. It was found that the IC50 and Ki values for the 4-amino-3-chloro benzohydroxamic acid molecule were 218.33 and 175.67 ± 43.78 μM, respectively, whereas the IC50 and Ki values for the 4-amino-2-methoxy benzohydroxamic acid molecule were 306.00 and 218.00 ± 68.80 μM, respectively. The HRP enzyme was synthesized from 4-amino-2-methoxy hydroxamic acid column with a 35.97% yield 601.13 times, 4-amino-3-nitro hydroxamic acid column, with a 14.00% yield 404.11 times, 4-amino-3-methyl hydroxamic acid column with an 8.70% yield 394.88 times, and 4-amino-3-chloro hydroxamic acid column with a 4.48% yield 284.85 times. Thus, the HRP enzyme was purified in a single step with hydroxamic acids, and its molecular weight was found to be 44 kDa. The optimum pH was 8.0, the optimum temperature was 15°C, and the optimum ionic strength was 0.4 M for the purified HRP enzyme.

Potential Implications of Hyperoside on Oxidative Stress-Induced Human Diseases: A Comprehensive Review

Hyperoside is a flavonol glycoside mainly found in plants of the genera Hypericum and Crataegus, and also detected in many plant species such as Abelmoschus manihot, Ribes nigrum, Rosa rugosa, Agrostis stolonifera, Apocynum venetum and Nelumbo nucifera. This compound exhibits a multitude of biological functions including anti-inflammatory, antidepressant, antioxidative, vascular protective effects and neuroprotective effects, etc. This review summarizes the quantification, original plant, chemical structure and property, structure-activity relationship, pharmacologic effect, pharmacokinetics, toxicity and clinical application of hyperoside, which will be significant for the exploitation for new drug and full utilization of this compound.

Enzymatic browning and polyphenol oxidase control strategies

Significant amounts of fresh and fresh-cut fruits and vegetables are wasted every year due to enzymatic browning. Polyphenol oxidase (PPO) is the key enzyme involved in the enzymatic browning. In the past decades, various methods have been developed to inhibit browning of various fresh produce items. However, for most fresh horticultural produce, ideal measures accepted by industries and consumers are still scarce. This review provides up-to-date knowledge of browning control technologies, including physical methods, chemical methods such as natural inhibitors, molecular biotechnology, and nanotechnology. In addition, we propose some ideas to improve the efficacies of these strategies with fewer side effects. To better inhibit tissue browning, new research directions are also discussed, for example, regulation of PPO substrate techniques.

The Relationship between the IC50 Values and the Apparent Inhibition Constant in the Study of Inhibitors of Tyrosinase Diphenolase Activity Helps Confirm the Mechanism of Inhibition

Tyrosinase is the enzyme involved in melanization and is also responsible for the browning of fruits and vegetables. Control of its activity can be carried out using inhibitors, which is interesting in terms of quantitatively understanding the action of these regulators. In the study of the inhibition of the diphenolase activity of tyrosinase, it is intriguing to know the strength and type of inhibition. The strength is indicated by the value of the inhibition constant(s), and the type can be, in a first approximation: competitive, non-competitive, uncompetitive and mixed. In this work, it is proposed to calculate the degree of inhibition (iD), varying the concentration of inhibitor to a fixed concentration of substrate, L-dopa (D). The non-linear regression adjustment of iD with respect to the initial inhibitor concentration [I]0 allows for the calculation of the inhibitor concentration necessary to inhibit the activity by 50%, at a given substrate concentration (IC₅₀), thus avoiding making interpolations between different values of iD. The analytical expression of the IC₅₀, for the different types of inhibition, are related to the apparent inhibition constant (KIapp). Therefore, this parameter can be used: (a) To classify a series of inhibitors of an enzyme by their power. Determining these values at a fixed substrate concentration, the lower IC₅₀, the more potent the inhibitor. (b) Checking an inhibitor for which the type and the inhibition constant have been determined (using the usual methods), must confirm the IC₅₀ value according to the corresponding analytical expression. (c) The type and strength of an inhibitor can be analysed from the study of the variation in iD and IC₅₀ with substrate concentration. The dependence of IC₅₀ on the substrate concentration allows us to distinguish between non-competitive inhibition (iD does not depend on [D]0) and the rest. In the case of competitive inhibition, this dependence of iD on [D]0 leads to an ambiguity between competitive inhibition and type 1 mixed inhibition. This is solved by adjusting the data to the possible equations; in the case of a competitive inhibitor, the calculation of KI1app is carried out from the IC₅₀ expression. The same occurs with uncompetitive inhibition and type 2 mixed inhibition. The representation of iD vs. n, with n=[D]0/KmD, allows us to distinguish between them. A hyperbolic iD vs. n representation that passes through the origin of coordinates is a characteristic of uncompetitive inhibition; the calculation of KI2app is immediate from the IC₅₀ value. In the case of mixed inhibitors, the values of the apparent inhibition constant of meta-tyrosinase (Em) and oxy-tyrosinase (Eox), KI1app and the apparent inhibition constant of metatyrosinase/Dopa complexes (EmD) and oxytyrosinase/Dopa (EoxD), KI2app are obtained from the dependence of iD vs. n, and the results obtained must comply with the IC₅₀ value.