Hydrolytic action of phospholipase A2 in monolayers in the phase transition region: direct observation of enzyme domain formation using fluorescence microscopy

[20] Giant vesicles, laurdan, and two-photon fluorescence microscopy: Evidence of lipid lateral separation in bilayers

“…The equilibration of fatty acid and lysolipid into the soluble phase creates structural stress on the outer leaflet of the membrane, where sPLA2 initially has access and begins active lipid hydrolysis. Given the partition coefficients for myristoyl-lysophosphatidylcholine (0.5 x 106) 76 and myristic acid (2.6 × 106),78the products would be expected to partition into the aqueous phase. In contrast, bulk solution measurements with large/medium/small unilamellar vesicles are usually performed at lipid concentrations of > 100 #M, where a significant fraction of the products would be expected to remain in the bilayer.…”

Protein-mediated surface structuring in biomembranes

“…A "dynamic" type of protein-induced surface structuring is mediated by the action of phospholipases (10,41). All phosphohydrolytic enzymes, usually a kind of amphitropic proteins producing lipid second messengers, are currently thought to be involved in some sort of membrane signal transduction process (42,43).…”

“…It is well documented that the activity and kinetics of lipases and phospholipases (mostly those of the A 2 and C types) are correlated with the existence of lateral membrane defects and structural domain microheterogeneity (41,46,47), coexistence of bilayer and non-bilayer phases (48,49) and with the presence of non-substrate lipids or proteins in the interface (21,39). Lipid mixing-demixing processes and concomitant structuring of segregated domains with different lipid composition or phase state profoundly influence the pre-catalytic and catalytic steps of the enzymatic reactions (10,41,45,49).…”

“…Lipid mixing-demixing processes and concomitant structuring of segregated domains with different lipid composition or phase state profoundly influence the pre-catalytic and catalytic steps of the enzymatic reactions (10,41,45,49). A common structural element in all of these factors is the existence of lateral and/or transverse packing defects and interface tensions introduced by changes of lipid composition, anisotropic interactions, phase coexistence and connectivity of the domain lattice (10,21,41,45,49).…”

“…Lipid mixing-demixing processes and concomitant structuring of segregated domains with different lipid composition or phase state profoundly influence the pre-catalytic and catalytic steps of the enzymatic reactions (10,41,45,49). A common structural element in all of these factors is the existence of lateral and/or transverse packing defects and interface tensions introduced by changes of lipid composition, anisotropic interactions, phase coexistence and connectivity of the domain lattice (10,21,41,45,49). Within this context, critical amounts of non-substrate lipids or proteins that may induce or disrupt specific surface super-structuring (10,45,47) over ranges that exceed the local intermolecular interactions become important membraneregulating factors, and some of the topological variations may be induced by the phosphohydrolytic enzymes themselves.…”