Characterization of Bovine and Human Lactoferrins as Glycyrrhizin-Binding Proteins and Their Phosphorylation in Vitro by Casein Kinase II

Abstract

The binding ability of bovine and human lactoferrins (bLF and hLF; LFs) to a glycyrrhizin (GL)-affinity column and their phosphorylation by casein kinase II (CK-II) in vitro were biochemically investigated. It was found that (i) both bLF and hLF are GL-binding proteins; (ii) purified both proteins function as phosphate acceptors of CK-II; and (iii) this phosphorylation is completely inhibited by two polyphenol-containing anti-oxidant compounds (quercetin and epigallocatechin gallate) at 1 μM, whereas a glycyrrhetinic acid derivative (oGA) inhibits it at one tenth the concentration of GL. The DNA-binding affinity of hLF was reduced by GL in a dose dependent manner. However, no significant effect of the CK-II-mediated hLF phosphorylation on its DNA-binding affinity was detected. These results suggest that the GL-induced inhibition of the DNA-binding affinity and the CK-II-mediated phosphorylation of hLF may be closely correlated with the anti-inflammatory effect of GL in the human body.