In vitro inhibitory effects of bergenin and norbergenin on bovine adrenal tyrosine hydroxylase.

The aqueous extract of Mallotus japonicus (Euphorbiaceae) showed an inhibitory effect on bovine adrenal tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine. The present study was undertaken to investigate the effects of bergenin and norbergenin, constituents of the aqueous extract of Mallotus japonicus on bovine adrenal TH. Bergenin and norbergenin inhibited the TH activity by 29.0% and 53.4% at a concentration of 20 microg/mL, respectively, and exhibited noncompetitive inhibition of TH activity with the substrate l-tyrosine. The inhibition of TH activity and the inhibitory effect of norbergenin was more potent than that of bergenin. From these results, it is presumed that bergenin and norbergenin may be the active components of Mallotus japonicus in inhibiting TH, and these inhibitory effects may be partially responsible for the clinical use of Mallotus japonicus in treating peptic ulcer by reducing the availability of dopa/dopamine in vivo.