Hydrolysis of [3H,4C] Phosphatidylethanolamines by Acid Phospholipases A of Subcellular Fractions of Rat Spleen

Abstract
Rat spleen exhibits maximal phospholipase A activity at pH 4.5. This activity is due to a phospholipase A1 and a phospholipase A2. After injection of Triton WR 1339, rat spleens were fractionated by differential centrifugation. The mitochondria + lysosomes fraction was further fractionated on a sucrose gradient. Three lysosomal populations were individualized of which the heavier one was sedimented with mitochondria.With phosphatidylethanolamines as substrate, phospholipase A1 and A2 are present in similar ratio in all the subcellular fractions and in the three lysosomal populations.Rat spleen is about 1.3‐fold richer in phospholipase A1 than in phospholipase A2. The fraction from centrifugation at 1000×g for 10 min contains respectively 40% and 44% of the total phospholipases A1 and A2 activities, the mitochondria + lysosomes fraction only 28% and 26%. Free ribonucleoprotein particles have low phospholipases A1 and A2 activities.

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