Evidence for the control of the action of phospholipases A by the physical state of the substrate

A model for the molecular mechanism of interfacial activation of phospholipase A2 supporting the substrate theory

“…The dipyrene phospholipids diPBPC and PBPHPC were chosen due to their ability to form intramolecular excimer [39] in addition to the intermolecular excimer and due to their different pyrene fatty acyl chains at the sn-2 position. We previously concluded that changes in intramolecular excimer formation can reflect changes in the conformation of dipyrene phospholipids [19,20,40]. If the model of the extended and kinked conformations of these pyrene phospholipids below and above CMC, respectively, were to be operative, a decrement in the rate of intrarnolecular pyrene excimer formation of diPBPC above CMC would be observed due to the non-alignment of the pyrene moieties at the end of the fatty acyl chains in the kinked conformation ( fig.2).…”

“…Changes in the very high Ie/Im observed in the presence of submicellar cholate suggested the formation of premicellar molecular aggregates by both pyrene phospholipids [42]. Therefore, changes in Ie/Im are likely to be due to changes in both inter-and intramolecular excimer formation rates [19,20,[38][39][40]. When the premicellar pyrene phospholipid aggregates disappear at CMC and pyrenephosphocholine molecules were distributed to mixed micelles by increasing cholate concentrations a decrement in 1=/lol should be seen.…”

“…PLA2 activities were determined with a Kontron SFM 23 spectrofluorometer as described [19,25,26]. The substrate was prepared by drying 10/zg pyrenephosphocholine with a gentle stream of nitrogen.…”

“…phospholipases A1 and A2 can be reciprocally regulated by changing the physical state of the substrate and proposed a model for conformational changes occurring in phospholipid molecules [19,20]. In our earlier study, however, liposomal and monolayer membranes were used to characterize electrostatically [21] induced alterations in substrate phospholipids and in PLA2 activities [19,20].…”

“…In our earlier study, however, liposomal and monolayer membranes were used to characterize electrostatically [21] induced alterations in substrate phospholipids and in PLA2 activities [19,20]. Therefore, the direct relevance of these results to the elucidation of the mechanism underlying PLA2 activation at the CMC is questionable as changes in the degree of substrate deprotonation were involved [21].…”