Inactivation of phospholipase A2 by naturally occurring biflavonoid ochnaflavone

초록

Ochnaflavone, a medicinal herb product isolated from Lonicera japonica, strongly inhibited rat platelet phospholipase A<inf>2</inf> (IC<inf>50</inf>, about 3 μM). Inactivation was concentration and pH dependent (maximum inactivation occurred between pH 9.0 and 10.0) Ochnaflavone inhibited the enzyme by a noncompetitive manner, with the apparent Ki value of 3 x 10-5 M. Reversibility was studied directly by dialysis method; the inhibition was irreversible. In addition, the inhibitory activity of ochnaflavone is rather specific against group II phospholipase A<inf>2</inf> than group I phospholipase A<inf>2</inf> (IC<inf>50</inf>, about 20 μM). Addition of excess Ca2+ concentration up to 8 mM did not antagonize the inhibitory activity of ochnaflavone. These results indicate that the inhibition of phospholipase A<inf>2</inf> by ochnaflavone may result from direct interaction with the enzyme. © 1994 Academic Press, Inc.