Alpha-substituted derivatives of
cinnamaldehyde (alpha-bromocinnamaldehyde,
alpha-chlorocinnamaldehyde, and alpha-methylcinnamaldehyde) were used
as inhibitors on mushroom tyrosinase. The result showed that three
compounds can reduce both monophenolase and diphenolase activity on
tyrosinase, and the inhibition was reversible. The IC
50 values of alpha-bromocinnamaldehyde, alpha-chlorocinnamaldehyde,
and alpha-methylcinnamaldehyde were 0.075, 0.140, and 0.440 mM on
monophenolase and 0.049, 0.110, and 0.450 mM on diphenolase, respectively.
The inhibition types and constants on diphenolase for these inhibitors
were further studied. The molecular inhibition mechanisms of tyrosinase
by the derivatives were investigated by UV-scanning study, fluorescence
quenching, and molecular docking. These assays demonstrated that the
derivatives could decrease the formation of o-quinones,
and all derivatives were static quenchers of mushroom tyrosinase.
Docking results implied that they could not form metal interactions
with the copper ions of the enzyme, whereas they could interact with
the amino acid residues of active site center. This research on alpha-substituted
derivatives of cinnamaldehyde as tyrosinase inhibitors would lead
to advances in the field of antityrosinase.
To investigate the effects of the simultaneous occurrence of salt stress and tidal sea-level rise on mangroves, potted Kandelia candel seedlings were treated under deep flooding (flooded 40 cm above the soil surface for 16 h per day, inundating the entire plant) and shallow flooding (flooded just above the soil surface for 8 h per day) at salinity levels of 5, 15, and 25 ppt over 14 months. Deep flooding enhanced stem elongations at all salinity levels but increased stem biomass only at 5 ppt. Deep flooding increased both leaf production and leaf fall; leaf biomass increased at 5 ppt, but decreased at 15 and 25 ppt. Biomass ratios of root/shoot (R/S) of deep flooding treatments were significantly lower than those of shallow flooding treatments. Under deep flooding, superoxide dismutase (SOD) activities did not show significant change between 5 and 15 ppt, but increased at 25 ppt. With increasing salinity level, peroxidase (POD) activities increased, and the difference between shallow and deep flooding was enhanced. Malonaldehyde (MDA) content significantly decreased at 25 ppt with 40 cm flooding, but was not affected by other treatments. These results demonstrated that the growth and physiological responses of K. candel seedlings under deep flooding conditions varied with salinity level; growth was enhanced at low salinity level but inhibited at high salinity level. It is therefore probable that K. candel will shift from downstream to upstream, where the influence of fresher river water resources will ameliorate the effects of increased salinities that accompany deeper tidal flooding in these mangrove ecosystems.
Tyrosinase is a key enzyme in post-harvest browning of fruit and vegetable. To control and inhibit its activity is the most effective method for delaying the browning and extend the shelf life. In this paper, the inhibitory kinetics of 4-hydroxy cinnamic acid on mushroom tyrosinase was investigated using the kinetics method of substrate reaction. The results showed that the inhibition of tyrosinase by 4-hydroxy cinnamic acid was a slow, reversible reaction with fractional remaining activity. The microscopic rate constants were determined for the reaction on 4-hydroxy cinnamic acid with tyrosinase. Furthermore, the molecular docking was used to simulate 4-hydroxy cinnamic acid dock with tyrosinase. The results showed that 4-hydroxy cinnamic acid interacted with the enzyme active site mainly through the hydroxy competed with the substrate hydroxy group. The cytotoxicity study of 4-hydroxy cinnamic acid indicated that it had no effects on the proliferation of normal liver cells. Moreover, the results of effects of 4-hydroxy cinnamic acid on the preservation of mushroom showed that it could delay the mushroom browning. These results provide a comprehensive underlying the inhibitory mechanisms of 4-hydroxy cinnamic acid and its delaying post-harvest browning, that is beneficial for the application of this compound.
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