Enzymatic characterization of the major phospholipase A(2) component of sea anemone (Aiptasia pallida) nematocyst venom

The purified beta phospholipase A(2) (PLA(2); EC 3.1.1.4) (PLA(2)) from sea anemone (Aiptasia pallida) nematocysts is larger and more labile than othe r known venom PLA(2)s. In common with all other known venoms and most secre tory PLA(2)s, the beta PLA(2) requires mM Ca2+ for optimal activity and is surface-activated by aggregated lipids such as mixed micelles of detergent and phospholipid. The beta PLA(2) exhibits an unusually steep and narrow pH optimum of activity at pH 7.7. The effects of changes in pH on the activit y of the enzyme suggest that the active site contains functional groups hav ing a pK's of about 7.0 and 8.0, The effects of temperature on beta PLA(2) activity show a marked decrease in the energy of activation above the pre-t ransition temperature, suggesting that the enzyme "melts" both fatty chains in order for catalysis to occur. (C) 2000 Elsevier Science Ltd. All rights reserved.