Comparison Study Between The Effects Of Inhibitors On The Activities Of Mushroom Tyrosinase And Potato Polyphenol Oxidase

Tyrosinase (EC 1.14.18.1) is also called polyphenol oxidase. It is a copper-containing enzyme that is widely distributed in microorganisms, animals and plants. It is called tyrosinase because it has the activity of monophenolase in fungi, bacterium and animals. It is a key enzyme during the melanin biosynthesis. Therefore, it is of significant to study the enzymetic character, catalytic mechanism and inhibition mechanism of the enzyme.This paper is composed of two parts. In the first part, we isolated and partially purified polyphenol oxidase from potato, and extracted the inhibitor of tyrosinase from persimmon leaf. In the second part we compared the inhibitory effects on the activities of mushroom tyrosinase and potato polyphenol oxidase by some chemical inhibitors and persimmon leaf extract.The results showed that it is more effective using 0.05 mol/L PBS buffer to isolate potato PPO than using acetone, especially for the varieties of low enzymic activity. The potato variety using in this study is No.1 Min Shu, the enzymic activity of which is weak. By this method, the potato PPO specific activity was determined to be 79.83 U/mg, purification multiple was 16.19 after partially purification.The inhibition strength on both of mushroom tyrosinase and potato PPO among these p-alkylbenzoic acid tested follows the order: p-octylbenzoic acid > p-heptylbenzoic acid > p-hexylbenzoic acid > p-pentylbenzoic acid > p-butylbenzoic acid > p-propylbenzoic acid. The inhibition strength is increasing while the hydrocarbon chain increasing. All of p-alkylbenzoic acid acting on mushroom tyrosinase was showed to be uncompetitive inhibitors, while belong to be noncompetitive inhibitors on potato PPO.The mushroom tyrosinase has the activity of monophenolase and diphenolase, while the potato PPO doesn't have the activity of monophenolase. The inhibition strength on both of mushroom monophenolase, diphenolase and potato PPO among these 4-halobenzoic acid tested follows the order: 4-bromobenzoic acid > 4-chlorobenzoic acid > 4-fluorobenzoic acid. For the diphenolase activity of both of mushroom tyrosinase and potato PPO, the inhibition displayed as reversible, and the inhibition types were all determined to be noncompetitive.The inhibitory effects of 4-methoxysalicylic acid are stronger than that of 5-methoxysalicylic acid on either of mushroom tyrosinase and potato PPO. They are all mix-typed inhibitors on mushroom tyrosinase, while noncompetitive inhibitors on potato PPO.The extract from persimmon leaf can obviously inhibit both of the enzymes tested, and the inhibition strength of the 50% ethanol extraction is stronger than that of the H2O extraction. They are all noncompetitive inhibitors on both of the enzyme.The inhibitory potency of geranyl gallate is as about six times as that of lauryl gallate on mushroom tyrosinase. Lauryl gallate was determined to be an uncompetitive inhibitor while geranyl gallate belongs to be a mixed-type inhibitor.The strongest inhibitor among the three fluorobenzaldehydes is 4-fluorobenzaldehyde, 3-fluorobenzaldehyde is medium, and 2-fluorobenzaldehyde is the weakest one. Furthermore, 2-fluorobenzaldehyde was determined to be a mixed-type inhibitor while 3-fluorobenzaldehyde and 4-fluorobenzaldehyde belong to be competitive inhibitors.In conclusion, the inhibitory effects are not all the same by identical inhibitor. The two enzymes come from different organism. All the results indicate that the structure of the two enzymes is mostly similar, and there are some differences between them. They are differential in genus.