Subcellular distribution and some properties of acid phospholipase A1 in rat testis

The activity of phospholipase A was studied in homogenates, and mitochondria and lysosome-enriched fractions of rat testis. Using testicular homogenates and Triton X-100, phospholipase A1 activity with pH optima at 3.0 and 7.0 and phospholipase A2 activity with a pH optimum at 6.5 were observed. With optimum pH at 3.0, phospholipase A1 was further studied, identified and characterized by using 1-acyl-2-[1-(14)C]1 oleoyl-sn-glycero-3-phosphocholine as substrate in mitochondria and lysosome-enriched fractions. Acid phospholipase A1 activity was inhibited by Ca2+ and EDTA. The enzyme activity was greatly stimulated by Triton X-100, not inhibited by sulfhydryl reagents and DIFP, and relatively heat stable at 65 degrees C. Acid phospholipase A1 activity had properties similar to other phospholipases of lysosomal origin: subcellular distribution, metal independence and acid pH optimum and was mainly localized in mitochondria and lysosome-enriched fraction suggesting a lysosomal origin.