Inhibitory Effect of Glycyrrhizin on the Phosphorylation

　　The physiological correlation between glycyrrhizin （GL） and high mobility group proteins 1 and 2 （HMG1/2） and the inhibitory effect of GL on their phosphorylation by three protein kinases （CK-I， CK-II and PKC） were investigated biochemically in vitro. It was found that GL binds directly to HMG1/2， because （i） HMG1/2 have a high affinity with a GL-affinity column； and （ii） GL induces the conformational changes in HMG1/2. Both purified HMG1/2 functioned as phosphate acceptors for these two protein kinases （CK-I and PKC）， but not phosphorylated by CK-II. Phosphorylation of HMG1/2 by two protein kinases （CK-I and PKC） was completely inhibited by a glycyrrhetinic acid derivative （oGA） at one-tenth the concentration of GL. Also， the DNA-binding abilities of HMG1/2 were reduced by GL in a dose-dependent manner. These results show that the binding of GL to HMG1/2 results in the inhibition of their physiological activities （DNA-binding ability and phosphorylation by PKC or CK-I） in vitro. The GL-induced inhibition of the physiological activities of HMG1/2 may be involved in the anti-inflammatory effect of GL in vivo.