The Inhibitory Effects Of Keggin-type Polyoxometalates And Two Food Additives On Tyrosinase

Tyrosinase(EC1.14.18.1,Tyrosinase)is a complex multifunctional oxidoreductase,which is widely present in animals,plants and microorganisms.The active center contains two copper ions.It has a variety of physiological activities.It is a key enzyme in the melanin production process.The color of human eyes,hair,and skin mainly depends on melanin.Abnormal melanin synthesis can lead to skin diseases such as freckles and melanoma.In fruits,vegetables and aquatic products,the production of melanin will reduce product quality.Therefore,we should research and develop tyrosinase inhibitors,which can effectively block the synthesis of melanin,and have good application prospects in the fields of food preservation,cosmetics whitening,and skin disease drugs.Polyoxometalates(POMs)are metal oxygen cluster compounds formed by the condensation of oxygen and early transition metals,referred to as POMs.POMs have various structural changes and various biological activities,and play an important role in biomedicine research.Studies have found that polyoxometalates show anti-cancer,anti-viral,anti-tumor,antibacterial,and anti-enzyme effects.POMs can be used as potential tyrosinase inhibitors for research.Food additives are used to improve food quality.They are natural/synthetic substances that are harmless or extremely low to the human body.Antioxidants can prevent or delay the oxidation reaction of food,thereby improving food quality and extending storage time.The special structure of antioxidants may interact with tyrosinase and change the activity of tyrosinase.Hence,this paper selects polyoxometalates and food additives as effectors,conducts enzyme kinetic experiments,studies the inhibitory effects of the two types of effectors and tyrosinase,and simulates the combination of the effectors and tyrosinase with the help of molecular docking technology.The main research content and results of this article are as follows:(1)Two Keggin-type polyoxometalates(galomolybdic acid and silomolybdic acid)with different heteroatoms were synthesized,and characterized with Fourier infrared spectrometer and ultraviolet-visible spectrophotometer.Enzyme kinetics experiments studied the inhibitory effects of effectors and tyrosinase,and molecular docking simulated the binding effect of compounds and tyrosinase.The experimental results showed that both compounds showed reversible competitive inhibition of tyrosinase.Among them,silicomolybdic acid(IC₅₀=8.859±0.491mmol/L)was more effective than gallomolybdic acid(IC₅₀=21.860±0.625 mmol/L).L).In addition,the central atom(heteroatom)charge,oxidation-reduction properties,and acid strength of POMs may be related to the significant difference in the inhibitory effect of tyrosinase.Molecular docking showed that the two POMs and tyrosinase were bound by non-covalent bonds,mainly hydrogen bonds and van der Waals forces.It also proved that the two compounds could reversibly inhibit tyrosinase.(2)Four kinds of transition metal vanadium-substituted Keggin-type phosphomolybdates Na_3+nPMo_12-nV_nO₄₀(n=2,3,4,5)were synthesized and characterized.The interaction between the compounds and tyrosinase was studied by enzyme dynamics and molecular docking simulation.The results of enzyme kinetics experiments showed that Na₅PMo₁₀V₂O₄₀ has the best inhibitory effect on tyrosinase,IC₅₀ value was 7.046±0.506 mmol/L.These four compounds all exhibit reversible mixed inhibition on tyrosinase.In addition,the inhibitory effect of the compounds on tyrosinase was affected by the number of transition metal vanadium substitutions.The molecular docking results showed that there were mainly two non-public valence interactions between the compound and tyrosinase:hydrogen bond and van der Waals force.(3)Propyl gallate and L-ascorbyl palmitate were selected as effectors,and enzyme kinetics experiments and molecular docking were conducted espectively.The results showed that the inhibition of tyrosinase by propyl gallate was reversible mixed type,IC₅₀=18.036±0.823 mmol/L,L-ascorbyl palmitate showed reversible anticompetitive inhibition,IC₅₀=2.806±0.082 mmol/L.The results of molecular docking showed that the two additives formed hydrogen bonds with the active center of tyrosinase and interacted with van der Waals forces.