Phospholipases A1 and A2 in bovine thyroid.

In both supernatant and sediment of thyroid tissue homogenate phospholipase and lysophospholipase activities were demonstrated. In the supernatant, using 1-acyl-2[1-14C]linoleoyl-sn-glycero-3-phosphorocholine in the presence of sodium taurocholate, phospholipase A1 activity with pH optima at 3.6 and 4.8 and phospholipase A2 activity with pH optima at 3.6 and 5.7 were found. The sediment showed mainly phospholipase A2 activity with a pH optimum at pH 6.5. Lysophospholipase activity (optimum pH 7--8), USING 1-[9,10-(3)H]stearyl-sn-glycero-3-phosphorocholine as a substrate was present in both supernatant and sediment. Enzyme assays performed on subcellular fractions suggest the soluble phospholipases to be of lysosomal origin and the solubilized phospholipase A2 activity of homogenate sediment to be of microsomal origin. Incubations with 3H-14C mixed labelled phosphatidylcholine further confirmed the above observations.