Inactivation of phospholipase A2 by naturally occurring biflavonoid, ochnaflavone.
Ochnaflavone, a medicinal herb product isolated from Lonicera japonica, strongly inhibited rat platelet phospholipase A2 (IC50, about 3 microM). 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 A2 than group I phospholipase A2 (IC50, about 20 microM). 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 A2 by ochnaflavone may result from direct interaction with the enzyme.
Chang
H W
HW
College of Pharmacy, Yeungnam University, Gyongsan, Korea.
Baek
S H
SH
Chung
K W
KW
Son
K H
KH
Kim
H P
HP
Kang
S S
SS
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology; D005419:Flavonoids / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D010741:Phospholipases A / Q000037:antagonists & inhibitors*; D054467:Phospholipases A2; D010946:Plants, Medicinal / Q000737:chemistry; D051381:Rats; D013379:Substrate Specificity
D005419:Flavonoids; C090940:ochnaflavone; D010741:Phospholipases A; D054467:Phospholipases A2