SUCCINATE DEHYDROGENASE .2. EFFECT OF PHOSPHOLIPASES ON PARTICULATE AND SOLUBLE SUCCINATE DEHYDROGENASE

1. 1.|The activity of beef-heart succinate dehyrogenase (succinate:(acceptor) oxidoreductase, EC 1.3.99.1) in particulate preparations is not affected by phospholipase A (phosphatide acyl-hydrolase, EC 3.1.1.4) but is inhibited by the action of phospholipase C (phosphatidylcholine cholinephosphohydrolase EC 3.1.4.3), and of phospholipase D (phosphatidylcholine phosphatidohydrolase, EC 3.1.4.4). 2. 2.|Washing of the preparation treated with phospholipase does not relieve the inhibition. Succinate dehydrogenase solubilized and purified from particulate preparations digested with phospholipase C shows a much lower activity than controls purified from undigested starting material. 3. 3.|Phospholipid hydrolysis in the particle is nearly complete after treatment with phospholipase A and C and only partially complete after treatment with phospholipase D. 4. 4.|Side reactions of the phospholipase C preparation have no detectable influence under our experimental conditions. 5. 5.|Soluble succinate dehydrogenase is not affected by the action of phospholipases, even if phosphatides are added to the mixture before treatment with phospholipases. 6. 6.|Except for phosphorylcholine, the products of phospholipase-catalyzed reactions do not affect the activity of soluble succinate dehydrogenase. Phosphorylcholine is a moderate mixed-type inhibitor and is only partly responsible for the inhibition folowing treatment with phospholipase C. It is suggested that phospholipases alterate the particulate flavoprotein by disrupting phospholipid organization in the membrane. 7. 7.|The inhibition by 2-thenoyltrifluoroacetone of succinate dehydrogenase activity is strongly decreased after treatment of the particles with any phospholipase. © 1969.