Table 2.
Effect of the ethanolic extract, fractions and the phyto-constituents identified in Aspalathus linearis on tyrosinase rate.
| Sample | Tyrosinase inhibition | Tyrosinase stimulation | Change in L-dopa kinetics | ||
|---|---|---|---|---|---|
| IC50 ± SD (µM)a | Fold increaseb | EC50 ± SD (µg/mL; µM)c | Vmaxd (µM/min) | Kme (µM) | |
| Substrate | |||||
| L-dopaf | N/Ag | N/A | N/A | 22.82 ± 1.07 | 143.80 ± 25.43 |
| Extract | |||||
| A. linearis EtOH extract | N/A | 0.40 | 105.10 ± 2.03 | 61.86 ± 8.69 | 104.00 ± 45.97 |
| Fractions | |||||
| Hex fraction | N/A | N/A | N/A | 120.10 ± 4.41 | 371.40 ± 29.38 |
| DCM fraction | N/A | N/A | N/A | 11.68 ± 3.43 | 2732 ± 1027 |
| EtOAc fraction | N/A | 0.67 | 51.23 ± 1.33 | 111.80 ± 4.90 | 99.75 ± 11.67 |
| EtOH fraction | N/A | 0.50 | 140.60 ± 2.69 | 26.47 ± 0.76 | 149.60 ± 12.83 |
| AcOH fraction | N/A | 0.38 | 83.48 ± 2.35 | 18.37 ± 0.63 | 31.79 ± 4.23 |
| H2O fraction | N/A | 0.25 | 84.02 ± 1.59 | 181.30 ± 25.28 | 500.70 ± 138.3 |
| Compounds | |||||
| Aspalathin (1) | N/A | 1.10 | 119.70 ± 2.06 (264.75 ± 4.56 µM) | 68.73 ± 3.47 | 1733 ± 660.60 |
| Caffeic acid (2) | N/A | 0.02 | 41.03 ± 3.54 (227.74 ± 19.65 µM) | 132.00 ± 24.50 | 2810 ± 874.6 |
| Catechin (3) | N/A | 0.40 | 143.30 ± 2.74 (493.70 ± 9.44 µM) | 382.40 ± 7.03 | 471.00 ± 26.43 |
| Cinnamic acid (4) | 943.58 ± 8.10 | N/A | N/A | 16.82 ± 0.37 | 269.90 ± 46.26 |
| Ferulic acid (5) | > 1500 | N/A | N/A | N/A | N/A |
| 4-Hydroxybenzoic acid (6) | 1868 ± 9.34 | N/A | N/A | 35.00 ± 1.84 | 267.20 ± 46.26 |
| Isoquercitrin (7) | > 646.42 | N/A | N/Ag | N/A | N/A |
| Luteolin (8) | N/A | N/A | N/A | 10.73 ± 1.01 | 232.10 ± 64.97 |
| p-Coumaric acid (9) | 152.58 ± 7.01 | N/A | N/A | 17.71 ± 0.66 | 254.00 ± 29.91 |
| n-Propyl gallate (10) | 534.87 ± 5.09 | N/A | N/A | N/A | N/A |
| Quercetin (11) | > 992.60 | N/A | N/A | 20.56 ± 1.72 | 110.80 ± 33.67 |
| Rosmarinic acid (12) | 7.33 ± 3.33 | N/A | N/A | N/A | N/A |
| Syringic acid (13) | > 1514 | N/A | N/A | 19.72 ± 1.01 | 401.10 ± 57.86 |
| Vanillic acid (14) | > 1784 | N/A | N/A | N/A | N/A |
| Vitexin (15) | > 693.83 | N/A | N/A | N/A | N/A |
| Kojic acidh | 14.79 ± 7.88 | N/A | N/A | N/A | N/A |
aAbsolute IC50 value, the concentration exhibiting 50% inhibition of the enzyme’s activity.
bDetermined as the enzyme rate of the sample divided by the enzyme rate of the vehicle control.
cRelative EC50 value, the concentration of the sample exhibiting 50% of its maximal response.
dVmax (maximum enzyme velocity).
eKm (michaelis constant—concentration of the sample where the enzyme reaches half of its Vmax).
fSubstrate.
gNot applicable/none active.
hPositive control.