Isolation and characterization of a cytosolic phospholipase a(2) from bovine adrenal-medulla
Faculty of Medicine and Health Sciences
Journal of neurochemistry. - Oxford
, p. 139-146
University of Antwerp
We have recently demonstrated that bovine adrenal medulla contains a soluble phospholipase A(2) (PLA(2)), which is localized in the cytosol. In the present study, this PLA(2) was purified 1,097-fold using sequential concanavalin A, hydrophobic interaction, anion exchange, gel filtration, and an additional anion exchange chromatography. The enzyme is activated over the range of 20-1,000 mu M Ca2+ and has a pH optimum near 8.0. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the protein has a molecular mass of 26 kDa and an isoelectric point of 4.6 as revealed by isoelectric focusing. The cytosolic PLA(2) is not inhibited by NaCl, and the enzymatic activity is stimulated at low concentrations of Triton X-100 (0.01%) and deoxycholate (1 mM) but inhibited at higher concentrations (0.1% and 3 mM, respectively) of these detergents. Furthermore, heat treatment (57 degrees C, 5 min) reduced the enzymatic activity by 80%, whereas glycerol (30%) increased the activity. p-Bromophenacylbromide, a frequently used irreversible inhibitor of type II PLA(2), has little effect until 100 mu M, and 2-10 mM dithiothreitol totally inactivated the enzyme. The purified PLA(2) displays a preference for phosphatidyl-choline as a substrate but hydrolyzes phospholipid substrates with arachidonic acid or linoleic acid esterified at the sn-2 position to the same extent. It is concluded that the chromaffin cell cytosolic PLA(2), which was isolated and characterized in this study, represents a type of PLA(2) that has not been formerly reported in chromaffin cells. Additional research on the chromaffin cell cytosolic PLA(2) will help to reveal whether the enzyme is important for exocytosis.