Table 3: Kinetic Parameters of Gallic Acid and Its Alkyl Esters for Superoxide Anion Generation by Xanthine Oxidasea)

Gallates Tested IC50µM)b) For Xanthine-Binding (µM)
KI KIS
Gallic acid (1) 2.6± 0.3 1.5± 0.2 2.9± 0.3
C1 (2) 7.4± 0.5 5.7± 0.4 8.0± 0.6
C3 (3) 6.4± 1.0c) 4.5± 0.5 6.8± 0.7
C6 (4) 5.2± 0.2c) 3.8± 0.4 5.3± 0.6
C8 (5) 4.5± 0.5c) 3.9± 0.2 4.7± 0.2
C10 (7) 3.9± 1.1c) 2.5± 0.6 4.8± 1.0
C12 (9) 3.6± 0.2c) 1.8± 0.2 4.4± 0.2
Menthyl(14) 4.9± 1.3c) 2.6± 0.4 4.9± 0.8
Bornyl(15) 6.4± 1.0c) 4.5± 0.3 6.3± 0.4

a) Xanthine oxidase reaction was carried out at 0-200µM xanthine in the presence of 0.0, 0.5, 1.0 and 2.0 µM of gallic acid or alkyl gallates under air atmosphere. Values were expressed as mean ± SD obtained from more than three separate experiments.
b) IC50values were indicated at 200 µM xanthine.
c) The value was estimated.