Determination of Phospholipases, Lipases, and Lysophospholipases

Phospholipid metabolism in the central nervous system is regulated by a variety of enzymes whose substrate specificities, cellular localizations, and regulatory mechanisms are only beginning to be understood. In brain, different phospholipids turn over at different rates with respect to their cellular structure, location, and the membranes mvolved (Freysz et al., 1976; Miller et al., 1977; Porcellati, 1983; Porcellati et al., 1983; Farooqui and Horrocks, 1985). The degradation of membrane phospholipids is a stepwise process that is catalyzed by various phospholipases and lysophospholipases (van den Bosch, 1982; Dennis, 1983). Acylglycerols, although quantitatively minor components of mammalian brain tissue (Rowe, 1969; Cook, 1981; Kunze et al., 1984), are very active and important metabolically (Berridge, 1984; Boni and Rando, 1985; Williamson et al., 1985). They are hydrolyzed by lipases called acylglycerol acylhydrolases. Studies on the isolation and characterization of brain lipases, lysophospholipases, and phospholipases are complicated by two major problems. The activities of these enzymes are quite low when compared with other hydrolytic enzymes. Second, rapid and sensitive assay procedures for the determination of their enzymic activities have not been available.