CHARACTERIZATION OF A NOVEL PHOSPHOLIPASE A(2) ACTIVITY IN HUMAN BRAIN

Phospholipases A(2) (PLA(2)) 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 l ittle is known regarding the status of PLA(2) activity in human CNS. W e therefore have characterized some aspects of the PLA(2) activity pre sent in the temporal cortex of human brain. More PLA(2) activity was f ound in the membrane (particulate) fraction than in the cytosolic frac tion. The enzyme could be solubilized from particulate material using 1 M potassium chloride, and was capable of hydrolyzing choline phospho glyceride (CPG) and ethanolamine phosphoglyceride (EPG), with a prefer ence (approximately eightfold) for EPG over CPG. When the solubilized particulate enzyme was subjected to gel filtration chromatography, PLA (2) activity eluted in a high molecular mass fraction (similar to 180 kDa). PLA(2) activity was weakly stimulated by dithiothreitol, strongl y stimulated by millimolar concentrations of calcium ions, and inhibit ed by brief heat treatment at 57 degrees C, bromophenacyl bromide, the arachidonic acid derivative AACOCF(3), 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 pr eviously characterized PLA(2)s, it differs in several key features.