Abstract
Kojic acid, β-arbutin, α-arbutin, and deoxyarbutin have been reported as tyrosinase inhibitors in many articles, but some contradictions exist in their differing results. In order to provide some explanations for these contradictions and to find the most suitable compound as a positive control for screening potential tyrosinase inhibitors, the activity and inhibition type of the aforementioned compounds on monophenolase and diphenolase of mushroom tyrosinase (MTYR) were studied. Their effects on B16F10 cells melanin content, tyrosinase (BTYR) activity, and cell viability were also exposed. Results indicated that α-arbutin competitively inhibited monophenolase activity, whereas they uncompetitively activated diphenolase activity of MTYR. β-arbutin noncompetitively and competitively inhibited monophenolase activity at high molarity (4000 µM) and moderate molarity (250–1000 µM) respectively, whereas it activated the diphenolase activity of MTYR. Deoxyarbutin competitively inhibited diphenolase activity, but could not inhibit monophenolase activity and only extended the lag time. Kojic acid competitively inhibited monophenolase activity and competitive–noncompetitive mixed-type inhibited diphenolase activity of MTYR. In a cellular experiment, deoxyarbutin effectively inhibited BTYR activity and reduced melanin content, but it also potently decreased cell viability. α-arbutin and β-arbutin dose-dependently inhibited BTYR activity, reduced melanin content, and increased cell viability. Kojic acid did not affect cell viability at 43.8–700 µM, but inhibited BTYR activity and reduced melanin content in a dose-dependent manner. Therefore, kojic acid was considered as the most suitable positive control among these four compounds, because it could inhibit both monophenolase and diphenolase activity of MTYR and reduce intercellular melanin content by inhibiting BTYR activity without cytotoxicity. Some explanations for the contradictions in the reported articles were provided.
Highlights
Excessive melanin synthesis involves many negative aspects of life, such as hyperpigmentation in the epidermis, affecting aesthetics and greatly increasing the risk of malignant melanoma [1], and enzymatic browning of fruits and vegetables, resulting in the undesirable reduction in nutrition and consumer acceptance [2,3]
The lag time of kojic acid for monophenolase activity was extended in a molarity-dependent manner, so too with α-arbutin, β-arbutin, Antioxidants 2022, 11, x FOR PEER REVIEW
The enzyme activity, which was reflected as the slope of the linear range of the kinetic curve, was reduced with the increasing molarity of kojic acid, α-arbutin, and β-arbutin in the reaction system
Summary
Excessive melanin synthesis involves many negative aspects of life, such as hyperpigmentation in the epidermis, affecting aesthetics and greatly increasing the risk of malignant melanoma [1], and enzymatic browning of fruits and vegetables, resulting in the undesirable reduction in nutrition and consumer acceptance [2,3]. Tyrosinase (EC 1.14.18.1) is a key enzyme for the biosynthesis of melanin and catalyzes two types of reaction: (a) monophenolase activity for the conversion of L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA), Antioxidants 2022, 11, 502. Antioxidants 2022, 11, 502 and (b) diphenolase activity for the oxidizing L-DOPA to o-dopaquinone. Inhibiting the activity of tyrosinase is an effective and important way to avoid melanin synthesis. Positive controls can be used to measure the inhibitory strength of a potentially effective inhibitor. Kojic acid and β-arbutin ( called arbutin) are well-known depigmenting agents and tyrosinase inhibitors [5–7]. They are commonly used as positive controls for screening emerging components or extracts that effectively inhibit melanin synthesis [5,8,9].
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