Activities of phospholipases A and lysophospholipases in glycolytic and oxidative skeletal muscles in the rabbit

Abstract

Oxidative muscles contain more free fatty acids than glycolytic muscles, which could explain in part their higher sensitivity to oxidation. These fatty acids are partly the result of phospholipid hydrolysis catalysed by phospholipases A and lysophospholipases. Up to now, very little is known on the activities of these enzymes in skeletal muscles. This study deals with the activities of phospholipases A and lysophospholipases in five rabbit muscles covering a large range of metabolic types (oxidative Soleus and Semimembranosus proprius muscles, glycolytic Psoas major and Longissimus lumborum muscles and intermediate Gastrocnemius laterale muscle). The results showed that (a) phospholipases A and lysophospholipases had maximal activity at pH 8-9; (b) phospholipases A and lysophospholipases retained more than 50% of their maximal activity at pH 5.5-6, the ultimate pH of muscles; (c) lysophospholipases exhibited a higher activity than phospholipases A (4-7-fold higher in the oxidative muscles, 11-fold higher in the intermediate muscle and 18-23-fold higher in the glycolytic muscles); and (d) phospholipase A and lysophospholipase activities were higher in oxidative muscles than in glycolytic muscles (10-25-fold higher for phospholipases A and 4-5-fold higher for lysophospholipases). Thus oxidative muscles have a higher potential activity for post-mortem hydrolysis of phospholipids. © 2000 Society of Chemical Industry.