Lysophospholipase in Brain Synaptosomes
Lysophospholipids are catalytic products of phospholipase A1 and A2. Their physiological significance in modulating membrane functions has been well recognized on account of their detergent properties. Lysophospholipids in brain are normally maintained at a very low level because two enzymic mechanisms are responsible for their degradation: (1) via reacylation back to the membrane phospholipids, and (2) further degradation by lysophospholipase. The lysophospholipase in brain is present in the membranous as well as cytosolic fractions. In brain synaptosomes, this enzyme exhibited a pH optimum of 8.0. It is sensitive to inhibition by both taurocholate and deoxycholate, but low level of Triton X-100 can stimulate its activity. The enzyme does not depend on calcium for activity; however, most divalent metal ions were potent inhibitors of the enzyme. The lysophospholipase did not show obvious specificity with respect to substrates with different polar head groups, but it preferred hydrolysis of saturated and monounsaturated acyl groups than the polyunsaturated acyl groups. Results here have indicated the role of lysophospholipase in protecting neural membranes from damage due to lysophospholipid accumulation. The coupled action of phospholipases A1 and A2 and lysophospholipase may be the underlying factor leading to the enormous amount of free fatty acid increase in membrane during brain stimulation and ischemia.