Abstract: Three kinds vanadate-replaced polyoxometalates, α-1,2,3-K6H[SiW9V3O40], α-1,2-K6[SiW10V2O40] and α-K5[SiW11VO40](abbreviated as α-SiW9V3, α-SiW10V2, α-SiW11V) were synthesized and evaluated as tyrosinase inhibitors using the enzymological kinetic method. The results demonstrate that α-SiW9V3 can inhibit tyrosinase strongly, as demonstrated by the inhibition of the steady-state activity of the enzyme and the lengthening of the lag time. The IC50 of α-SiW9V3 was estimated to be 0.6841 mmol/L for the inhibition of mushroom tyrosinase. It resulted in the lag time of the monophenolase extension from 235 s to 650 s with 0.7 mmol/L of α-SiW9V3. The inhibition of α-SiW9V3 on monophenolase of mushroom tyrosinase proceeds as reversible process, and the inhibition of α-SiW9V3 is a competitive-uncompetitive mixed-Ⅱ type due to the oxidation of L-tyrosine. The inhibition constants(KI and KIS) are determined to be 4.22 mmol/L and 2.39 mmol/L, respectively. As for the α-SiW10V2, however, it is unsoluble in DMSO buffer, and its effect on the mushroom tyrosinase cannot be studied. While the inhibition ability of α-SiW11V on tyrosinase activity is rather weak.

Key words: polyoxometalate, mushroom tyrosinase, monophenolase activity, Inhibition effect