INACTIVATION OF PHOSPHOLIPASE A(2) BY NATURALLY-OCCURRING BIFLAVONOID, OCHNAFLAVONE

Ochnaflavone, a medicinal herb product isolated from Lonicera japonica , strongly inhibited rat platelet phospholipase A(2) (IC50, about 3 mu M). Inactivation was concentration and pH dependent (maximum inactiva tion occurred between pH 9.0 and 10.0). Ochnaflavone inhibited the enz yme by a noncompetitive manner, with the apparent Ki value of 3 x 10(- 5) M. Reversibility was studied directly by dialysis method; the inhib ition was irreversible. In addition, the inhibitory activity of ochnaf lavone is rather specific against group II phospholipase A(2) than gro up I phospholipase A(2)(IC50, about 20 mu M). Addition of excess Ca2concentration up to 8mM did not antagonize the inhibitory activity of ochnaflavone. These results indicate that the inhibition of phospholip ase A(2) by ochnaflvone may result from direct interaction with the en zyme. (C) 1994 Academic Press, Inc.