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

Oxidative muscles contain more free fatty acids than glycolytic muscles, wh ich could explain in part their higher sensitivity to oxidation. These fatt y acids are partly the result of phospholipid hydrolysis catalysed by phosp holipases 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 muscle s covering a large range of metabolic types (oxidative Soleus and Semimembr anosus proprius muscles, glycolytic Psoas major and Longissimus lumborum mu scles and intermediate Gastrocnemius laterale muscle). The results showed t hat (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) lysopho spholipases exhibited a higher activity than phospholipases A (4-7-fold hig her 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 glyco lytic muscles (10-25-fold higher for phospholipases A and 4-5-fold higher f or lysophospholipases). Thus oxidative muscles have a higher potential acti vity for post-mortem hydrolysis of phospholipids. (C) 2000 Society of Chemi cal Industry.