Characterization of a novel phospholipase A2 activity in human brain.

Phospholipases A2 (PLA2) are a family of enzymes that catalyze the removal of fatty acid residues from phosphoglycerides. The enzyme is postulated to be involved in several human brain disorders, although little is known regarding the status of PLA2 activity in human CNS. We therefore have characterized some aspects of the PLA2 activity present in the temporal cortex of human brain. More PLA2 activity was found in the membrane (particulate) fraction than in the cytosolic fraction. The enzyme could be solubilized from particulate material using 1 M potassium chloride, and was capable of hydrolyzing choline phosphoglyceride (CPG) and ethanolamine phosphoglyceride (EPG), with a preference (approximately eightfold) for EPG over CPG. When the solubilized particulate enzyme was subjected to gel filtration chromatography, PLA2 activity eluted in a high molecular mass fraction (approximately 180 kDa). PLA2 activity was weakly stimulated by dithiothreitol, strongly stimulated by millimolar concentrations of calcium ions, and inhibited by brief heat treatment at 57 degrees C, bromophenacyl bromide, the arachidonic acid derivative AACOCF3, gamma-linolenoyl amide, and N-methyl gamma-linolenoyl amide. Thus, whereas the human brain enzyme(s) characterized in our study displays some of the characteristics of previously characterized PLA2s, it differs in several key features.