Abstract: AIMTo study the direct effect and kinetics of sodium quercetin-7,4′-disulphate (SQDS) on recombinant human protein kinase CK2 holoenzyme. METHODSThe recombinant human CK2 holoenzyme activity was assayed by detecting incorporation of ³²P of ［γ-³²P］ATP into the substrate in various conditions. RESULTSThe recombinant human CK2 was a second messenger (Ca²⁺, cAMP and cGMP) independent protein kinase. The characterization and function of the reconstituted holoenzyme were consistent with those of native CK2. SQDS was shown to strongly inhibit the holoenzyme activity of recombinant human protein kinase CK2 with an IC₅₀ of 4.4 μmol·L^-1, which was more effective than DRB and A3, known CK2 special inhibitors. Kinetic studies of SQDS on recombinant human CK2 showed: the inhibition was competitive with ATP and noncompetitive with casein. CONCLUSIONSQDS is a potent inhibitor of protein kinase CK2. This study provide experimental basis for the development of more effective inhibitors of CK2 and for clinical application of SQDS in the future.