Competition between cations and water for binding to phosphatidylcholines in organic solvents

Abstract

Cation binding to phosphatidylcholines in methanol is competitively inhibited by water. The binding of four water molecules per phosphatidylcholine prevents the binding of the

Thermodynamic model for micelle formation by phosphatidylcholines containing short-chain fatty acids. Correlations with physical-chemical data and the effects of concentration on the activity of phospholipase A2

“…Since the model was developed by combining two prototype micelles, i.e., DiC6 near the cmc represents micelle I and DiC8 represents micelle II, it is interesting to note that the conclusion that DiC6 micelle II is the substrate for phospholipase A2 is in accord with the general observation that DiC8 is the best substrate for this enzyme (de Haas et al, 1971;Wells, 1974a). Furthermore, Fmax for hydrolysis of DiC6 micelle II [(12-14) X 103 (qequiv/min)/mg] compares favorably to values for DiC8 under a variety of conditions [(5-15) X 103 (gequiv/min)/mg] (Misiorowski & Wells, 1973;Wells, 1974a). That the DiC6 micelle II and DiCs have approximately the same kinetic constants for hydrolysis by phospholipase A2 suggests the optimal interfacial structure is approximately independent of chain length.…”

How do ions contribute to brine-hydrophobic hydrocarbon Interfaces? An in silico study

“…of CaCl 2 solution indicates the presence of calcium ions around the toluene molecules. This might be due to the fairly strong hydration shell of Ca 2+ [61,62], which ties that ion to water molecules covering the surface of toluene molecules at the interface. The stronger interface affinity of Ca 2+ than Na + could also be interpreted on the basis of cation-p interaction, i.e., the favoring association of cations with bare plane of aromatic rings [57].…”

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

“…These results can be taken to support the 'substrate theory' of PLA2 activation at the CMC [4][5][6][7][8][9][10][11] as they reflect changes in the conformation of phospholipids due to incorporation of the lipid into a mixed micelle. The observed changes in the lipid conformation influencing the action of PLA2 also seem to be in line with our earlier model developed on the basis of results from a distinctly different experimental approach [20,21].…”

“…However, the zymogen of pancreatic PLA2 is not activated at interfaces [3]. The most feasible explanations for the interfacial activation are: (i) the substrate theory which assumes substrate molecules to be in interfaces in a conformation different from that in monomolecular solutions and resulting in an enhanced PLA2 activity [4][5][6][7] or alternatively, assumes the dehydration of interfacial substrate to be responsible for the interfacial activation [8][9][10][11] and (ii) the enzyme theory which assumes a conformational change in the enzyme molecule upon adsorption to the interface [3,12,13]. These models are not mutually exclusive.…”