Functionality Study Of Polyoxometalates As Tyrosinase Inhibitor

Tyrosinase（EC 1.14.18.1）is a multifunctional metal oxidase and the key enzyme in melanin biosynthesis.This enzyme can oxidase phenolic compounds to form melanin,which causes the browning of fruits and vegetables and skin pigmentary disorders of human body as well as protect insects from skin injuries.Therefore,the search for safe and efficient tyrosinase inhibitors has very important significance in medicine,agriculture,food chemistry and many other fields.Polyoxometalates（POMs）have been the subject of a large number of studies due to their multiplicate structures and functional properties,and their wide range of applications in many fields.Moreover,a lot of researchers considered that POMs might become potential effective enzyme inhibitors.Therefore,two kinds of Keggin-type polyoxometalates were synthesized and characterized.The inhibitory effects of compounds on mushroom tyrosinase and their antimicrobial activities were investigated.Furthermore,the biological effects of the compounds on B16 melanoma cells and the preservation of fruits and vegetables were studied.This paper aims to provide experimental basis for designing novel effective tyrosinase inhibitors and food preservatives and extending the use of polyoxometalates.The main contents and results of this paper are summarizd as follows:（1）Two kinds of Keggin-type polyoxometalates Na_9-nPMo₁₁MnO₄₀（Mⁿ=Cu^Ⅱ,Zn^Ⅱ,V^Ⅴ,Fe^Ⅲ）and [HGly]_9-nPMo₁₁MⁿO₄₀（Mⁿ=Cu^Ⅱ,Zn^Ⅱ,V^Ⅴ,Fe^Ⅲ）were synthesized.The inhibitory effects of compounds on the diphenolase activity of mushroom tyrosinase were evaluated by electrophoresis and spectrophotometry.The results showed that these compounds were potent inhibitors of tyrosinase.The inhibition effects of [HGly]_9-nPMo₁₁MⁿO₄₀（Mⁿ=Cu^Ⅱ,Zn^Ⅱ,V^Ⅴ,Fe^Ⅲ）on tyrosinase were all irreversible,which were more effective than Na_9-nPMo₁₁MⁿO₄₀（Mⁿ=Cu^Ⅱ,Zn^Ⅱ,V^Ⅴ,Fe^Ⅲ）.However,Na_9-nPMo₁₁MⁿO₄₀（Mⁿ=Cu^Ⅱ,Zn^Ⅱ,V^Ⅴ,Fe^Ⅲ）were all reversible inhibitors and showed different inhibition type.（2）The phosphomolybdate salts with different substituted transition metal ions(PMo₁₁Cu,PMo₁₁Zn,PMo₁₁V,PMo₁₁Fe)were tested for their antibacterial activities against S.lutea,S.aureus,B.subtilis and E.coli.The results showed that four compounds have obvious inhibition effects on all the bacteria,and the antimicrobial activities of all compounds on S.lutea and S.aureus were more effective than B.subtilis and E.coli.Moreover,the antimicrobial activity of PMo₁₁V was more effective than other three compounds.（3）The inhibitory effects of PMo₁₁Cu and PMo₁₁Fe on cell shape,cell viability,cellular tyrosinase activity and melanin formation in B16 melanoma cells were evaluated.The results showed that there were obvious changes of the B16 cell shape,cell viability,enzyme activity and melanin content when the concentrations of PMo₁₁Cu and PMo₁₁Fe reached a certain degree.（4）The effects of PMo₁₁Fe on the preservation of lotus root slices were studied.The results showed that PMo₁₁Fe could significantly slow the browning rate of the lotus root slices,inhibit the activity of PPO,enhance the activity of POD and SOD,maintain high levels of glutathione,ascorbic acid and sucrose,and finally control the senescence and browning of fresh-cut lotus root slices,as well as maintain the flavors and nutrients of lotus root slices.