Valonea Tannin: Tyrosinase Inhibition Activity, Structural Elucidation and Insights into the Inhibition Mechanism
Authors: Jacqui M McRae
Xiaofeng He
Bo Teng
Yuqing Liu
Jiaman Liu
Journal: Molecules (2021)
Discipline: CHEMISTRY
Keywords: enzyme binding; enzyme inhibition; hydrolysable tannin; inhibition mechanism; tyrosinase

Abstract:  Valonea tannin is a natural product readily extracted from acorn shells that has been suggested to have potential skin whitening properties. This study investigated the tyrosinase inhibition activity of extracted valonea tannin and the associated structure-function activity. Nuclear magnetic resonance spectroscopy and molecular weight analysis with gel permeation chromatography revealed that valonea tannin could be characterized as a hydrolysable tannin with galloyl, hexahydroxydiphenoyl and open formed-glucose moieties and an average molecular weight of 3042 ± 15 Da. Tyrosinase inhibition assays demonstrated that valonea tannin was 334 times more effective than gallic acid and 3.4 times more effective than tannic acid, which may relate to the larger molecular size. Kinetic studies of the inhibition reactions indicated that valonea tannin provided tyrosinase inhibition through mixed competitive-uncompetitive way. Stern-Volmer fitted fluorescence quenching analysis, isothermal titration calorimetry analysis and in silico molecule docking showed valonea tannin non-selectively bound to the surface of tyrosinase via hydrogen bonds and hydrophobic interactions. Inductively coupled plasma-optical emission spectroscopy and free radical scavenging assays indicated the valonea tannin had copper ion chelating and antioxidant ability, which may also contribute to inhibition activity. These results demonstrated the structure-function activity of valonea tannin as a highly effective natural tyrosinase inhibitor that may have commercial application in dermatological medicines or cosmetic products. 

Retracted: No

PubPeer comments:
 Figure 8: There is an overlap, I ve added the red rectangles to show where I mean. Would the authors please comment? ![file] , 
 Figure 6: *B. subtilis* and *S. aureus* images appear to be from the same plate. The pattern of colonies matches exactly at point d. I ve added the red ellipses and adjusted the contrast to help visualize this. ![file] , 
 Figure 8: There is an overlap, I ve added the red rectangles to show where I mean. Would the authors please comment? In the images for anti proliferative effect of different concentrations of AgNPs on MCF-7cell lines -25ug ml and 50 ug ml apparently looking similar and replication of images, But this is nit true in cytopathological view of the pointed out area .I HAVECHECKED UNDER HIGH MAGNIFICATION AND NOTED A A LOT OF CYRTOPATHOLOGICAL DIFFERNCES IN THAT AREAS.in 50ug ml image One can see1.loss of integrity among cells more prominent 2,Many cells have lost their cytoplasm and it is like a rim in periphery. The nuclei are highly polymorphic proving their dysfunction- Pycnotic. karyomegaly. attenuated. elliptical, pushed out of cells. broken cell division a, apoptosis leads to cell cell wall disintegration and nuclei are in vacuoles . Like wise several changes can be seen. But as the dose is less in 25ug ml exposure the cytopathological changes are less in type pointed areas. This is so vivid under higher magnification. Further both are same cell line the nuclear aberrations may be dose dependent and small deviation, This does not mean manipulation or mistake. A CLOSE CYTOPATHOLOGICAL MAGIFIED VIEW CAN DIFFERENTIATE. But in the MS this particular zone is not magnified as it is self explanatory. So Respected reader pl. try to observe in a cytopathological perspective under high power . I regret that I have not elaborated the cyopathological changes and katryotoxicity with high power images . Figure 6: B. subtilis and S. aureus images appear to be from the same plate. The pattern of colonies matches exactly at point d. I ve added the red ellipses and adjusted the contrast to help visualize this. Reply :Figure 6: B. subtilis and S. aureus images not from same plate-WHY? 1.If both are from same plate why there is a lot of difference in the zone of inhibition in other areas Eg .pl. see the magnified view of the central one 2. Pl. view  b in both plates 3. when the bug of different species respond similarly there is a possibility in well diffusion images 4. The zone of inhibition can not be manipulated .The position of ZoI is original and it cant be relocated by any manipulation. 5. In biological sample such similarity is possible . 6. The report is genuine although apparently similar like identical expression. The diameter of ZoI also varies. This is for your kind attention. After your comment I studied the images ordinal under high power and found many differences. THANKS FOR YOUR CTIRICAL VIEW .THIS WILL HELP THE AUTHOURS TO CLICK THE IMAGES METICULOUSLY IN FUTUREWORK. or antiproliferative effect , 
 #2 I agree with your observation. Author #3, please see the animation below (click on image): ![file] After enhancing the brightness on the aureus image it can also be seen that the background outside the dish nicely aligns, focus e.g. on the feature middle-right or top-left (click to animate): ![file] , 
 #1 Also agree with this overlap. Author #3, can you please point out the CYRTOPATHOLOGICAL DIFFERNCES IN THAT AREA ? And explain why one can obtain an identical arrangement of cells for different experiments? [ click to animate ] ![file] , 
 #3 With all due respect the authors should check the data again, the similarities are not adequately explained by Sandhanasamy Devanesan s comment. Thanks to Orchestes quercus for the animations! Cells don t arrange themselves in matching patterns between different experimental conditions. ,