Action of phospholipase A2 on unmodified phosphatidylcholine bilayers: Organizational defects are preferred sites of action

Abstract

The hydrolytic action of the bee venom phospholipase A2 on phosphatidylcholine bilayers is studied under a variety of conditions that introduce alterations in the packing, such as those induced by sonication, gel to liquid crystalline phase transition, and osmotic shock. Two phases of hydrolysis could be resolved under a wide range of experimental conditions. With the various forms of the bilayers one observes only a partial hydrolysis of the total available substrate during the first phase. However, the fraction of the substrate hydrolyzed in the first phase changes with the form of the available substrate, with the amount of the enzyme added, with the temperature, with the phase transition characteristics of the substrate, and by the sonication of the substrate. The second phase of hydrolysis is generally observed when a certain concentration of the products has been produced during the first phase of hydrolysis. These obervations are interpreted to suggest that the bee venom phospholipase A2 preferentially catalyzes hydrolysis of the substrate available at or near the defects in the organization of the substrate in the bilayers.

Synergy by Secretory Phospholipase A2 and Glutamate on Inducing Cell Death and Sustained Arachidonic Acid Metabolic Changes in Primary Cortical Neuronal Cultures

“…Also, nerve growth factor, a regulator of mast cell function, has been reported to potentiate sPLA 2 -induced histamine release (65). These observations suggest that sPLA 2 actively hydrolyzes lipids in disorganized membrane areas (66). Further studies combining lower, nontoxic concentrations of Glu and mammalian sPLA 2 type II, present together with Glu in synaptic vesicles (23), may further elucidate the involvement of both agonists in AA mobilization during glutamatergic synaptic activity.…”

Phospholipase A2 at the bilayer interface

“…As shown in Figure 6, these curves have a latency period which changes with thermotropic and isothermal phase transition characteristics of the substrate bilayer. 1~12.34, 35 The latency period is not observed if the products of hydrolysis are present in the vesicles. Such a kinetic behavior is best explained in w b+r--+ terms of a product-dependent shift in the E to E* Binding of PLAB to DTPC vesicles is not observed at, below, or above the phase transition temperature, nor is it seen in bilayers containing neutral amphiphiles.…”

Characterization of Phospholipase Activity of the Pseudomonas aeruginosa Type III Cytotoxin, ExoU

“…Unfortunately, in those studies, lysoPC was presented to rExoU as micelles, while the PC substrate was contained in DPPC gelphase vesicles (11). Most PLA 2 enzymes have high activity in bilayers around the melting temperatures of substrates and only weakly hydrolyze phospholipids from gel-phase bilayers (8,19), contributing to the minimal phospholipase activities reported. The ability of rExoU to hydrolyze lysoPC is not surprising, given that cPLA 2 hydrolyzes 1-palmitoyl-2-lysoPC and patatin cleaves monoacylglycerol and monoacylglycolphosphocholines (2,10,13).…”

“…rExoU substrate specificity was quantified by using honeybee phospholipase A 2 (PLA 2 ) as a positive control (19,21). rExoU hydrolyzed radiolabeled POPC at a level equivalent to 141% of that hydrolyzed by honeybee PLA 2 ( Table 2)…”