Regional distribution, ontogeny, purification, and characterization of the Ca2+-independent phospholipase A2 from rat brain

We purified an 80-kDa Ca 2+ -independent phospholipase A 2 (iPLA 2 ) from rat brain using octyl-Sepharose, ATP-agarose, and calmodulin-agarose column chromatography steps. This procedure gave a 30,000-fold purification and yielded 4 μg of a near-homogeneous iPLA 2 with a specific activity of 4.3 μmol/ min/mg. Peptide sequences of the rat brain iPLA 2 display considerable homology to sequences of the iPLA 2 from P388D 1 macrophages, Chinese hamster ovary cells, and human B lymphocytes. Under optimal conditions, the iPLA 2 revealed the following substrate preference toward the fatty acid chain in the sn-2 position of phosphatidylcholine: linoleoyl > palmitoyl > oleoyl > arachidonoyl. The rat brain iPLA 2 also showed a head group preference for choline ≥ ethanolamine » inositol. The iPLA 2 is inactivated when exposed to pure phospholipid vesicles. The only exception is vesicles composed of phosphatidylcholine and phosphatidylinositol 4,5-bisphosphate. Studies on the regional distribution and ontogeny of various phospholipase A 2 (PLA 2 ) types in rat brain indicate that the iPLA 2 is the dominant PLA 2 activity in the cytosolic fraction, whereas the group IIA secreted PLA 2 is the dominant activity in the particulate fraction. The activities of these two enzymes change during postnatal development.