Abstract:

The inhibitory effects of oolong tea polyphenols, EGCG and EGCG3”Me on α-glucosidase were comparatively
investigated by enzyme kinetics and UV absorption spectroscopy, and the possible mechanisms involved were explored. The
results showed that oolong tea polyphenols, EGCG and EGCG3”Me all had inhibitory effects on the activity of α-glucosidase,
and the half inhibitory concentration (IC50) values were 0.178, 0.040 and 0.064 mg/mL, respectively. The Lineweaver-
Burk double reciprocal plot indicated that the inhibition type of oolong tea polyphenols and EGCG was non-competitive
inhibition, whereas EGCG3”Me was competitive inhibition. Furthermore, oolong tea polyphenols could induce a blueshift
in the UV absorption maximum of α-glucosidase, suggesting the possible change in enzyme conformation. The differences
in inhibitory effects and inhibition types between EGCG and EGCG3”Me may be due to their structural difference (the
hydroxyl group in EGCG substituted by methoxy group to form EGCG3”Me).

Key words: oolong tea polyphenols, (－)-epigallocatechin gallate (EGCG), epigallocatechin3-O-(3-O-methyl) gallate(EGCG3’’Me), α-glucosidase, UV absorption