Objective: To observe the effect of 7 flavonoids on recombinant human protein kinase CK 2 holoenzyme activity and investigate their structure-activity relationship.
Methods: Recombinant human protein kinase CK 2 alpha' and beta subunits were mixed at equal molar ratio to reconstitute CK 2 holoenzyme. The CK 2 activity was assayed by detecting incorporation of (32)P of [gamma-(32)P]ATP into the substrate for the inhibitory effect by flavonoids and calculation of IC50 was performed according to probability unit (PROBIT) method.
Results: Myricetin, quercetin, morin, luteolin, kaempferol, apigenin, and chrysin were shown to obviously inhibit recombinant CK 2 holoenzyme activity in a concentration-dependent manner with IC50 values of 1.18, 0.51, 16.16, 0.86, 1.88, 1.72, and 13.63 micromol/L, respectively. Myricetin, quercetin, luteolin, kaempferol, and apigenin were more effective than DRB and A3, which were known as CK 2 inhibitors in vitro. Whereas morin and chrysin displayed a similar effect to DRB. Structure-activity study indicated that the major structural requirements for the potent inhibition of CK 2 by these flavonoids were hydroxyl group at position 6, 3' and 4'. Different from these requirements, absence of a hydroxyl group at position 3 did not modify their inhibitory potency, while addition of hydroxyl groups at positions 2' or 5' was detrimental to the inhibitory effect on CK 2.
Conclusion: The inhibitory effect of flavonoid on protein kinase CK 2 in vitro may be determined by the position of their hydroxyl groups.