Phospholipases bilayer

In studies with specific phospholipases the asymmetry in the composition of the lipid bilayer was also suggested [102,162]. The requirement of specific phospholipids, which are essential for enzyme activity, however, has not been established. For example, Saccomani et al. [102] demonstrated that readdition of various phospholipids, after phospholipase A2 treatment, results in a restoration of the K -ATPase activity. On the other hand, Nandi et al. [161] observed a restoration of the K -ATPase activity with addition of phosphatidylcholine and not with phosphatidyl-... 

MICELLAR SUBSTRATES. Phospholipids in micelles are frequently found to be more active substrates in lipolysis than those phospholipids residing in a lipid bilayer". Dennis first described the use of Triton X-100 to manipulate the amount of phospholipid per unit surface area of a micelle in a systematic analysis of the interfacial interactions of lipases with lipid micelles. Verger and Jain et al have presented cogent accounts of the kinetics of interfacial catalysis by phospholipases. The complexity of the problem is illustrated in the diagram shown in Fig. 2 showing how the enzyme in the aqueous phase can bind to the interface (designated by the asterisk) and then become activated. Once this is achieved, E catalyzes conversion of S to release P. ... 

Structure-Function Dissection and sequence analysis of phospholipases A2, 197, 201 cloning, expression, and purification of porcine pancreatic phospholipase A2 and mutants, 197, 214 preparation of antibodies to phospholipases A2, 197, 223 thermodynamics of phospholipase A2-ligand interactions, 197, 234 activation of phospholipase A2 on lipid bilayers, 197, 249 ... 

Dawson and I (Biochim. Biophys. Acta 59, 103, 1961) studied the interaction of two phospholipases with their common substrate, lecithin, and concluded that the enzyme must extend an active site ( masculine enzyme) into the planar lecithin monolayer or bilayer, respectively, in order to reach the ester bond. The phospholipase A2 from penicillin notaton required a net negative charge at the substrate surface, the a toxin from Cl. welchii, a positive one, to facilitate penetration. 

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... 

The cq receptors are activated not only by catecholamines but also by the hormones vasopressin and angiotensin n. Binding of these hormones to a, receptors induces a complex response that involves rapid hydrolysis of phosphatidylinositol derivatives and release of Ca2+ into die cytoplasm, and of diacylglycerols into the lipid bilayer of the membrane. The response is mediated by another G protein called Gq.27 1 275 When this G protein is activated it induces the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2), a normal minor component of the lipid bilayer, by phospholipase C (phosphoinositidase C).265,276 281... 

The diacylglycerols released by phospholipase C diffuse laterally through the bilayer and, together with the incoming Ca2+, activate protein kinases C. These kinases also require phosphatidylserine for their activity and phosphorylate serine and threonine side chains in a variety of proteins.329 330b They are stimulated by the released unsaturated diacylglycerols. In addition protein kinases C can be activated by phorbol esters, which are the best known tumor promoters (Box 11-D). The diacylglycerol requirement favors a function for these protein kinases in membranes. They also appear to cooperate with calmodulin to activate the Ca2+-dependent contraction of smooth muscle.330... 

The second cause may be due to steric hinderance of neighboring components within the myelin sheath. However, we found that digestion of trypsin or phospholipase C cannot alleviate the problem. In addition, hypotonic treatment of myelin which affects the integrity of the bilayer and also causes the splitting of the lamellae at the external apposition (19, 20), did not result in the oxidation of the cerebrosides. Even cerebrosides in liposomes made from pure phosphatidyl choline could not be oxidized. Incidentally, this finding also contradicts Linington and Rumsby who reported significant oxidation of cerebrosides in liposomes made from myelin lipids. 

Chifen AN, Forch R, Knoll W et al (2007) Attachment and phospholipase A2-induced lysis of phospholipid bilayer vesicles to plasmapolymerized maleic anhydride/Si02 multilayers. Langmuir 23 6294-6298... 

Stretch-activated proteins in animal cell membranes that are candidates for osmosensing activity include mechanosensitive ion channels and the membrane-localized enzyme phospholipase A2 (PLA2). The former proteins remain to be conclusively linked to osmosensing. Activity of PLA2 is sensitive to packing of the lipid bilayer of the cell and is responsive to osmotic changes, two attributes that mark it as a prime candidate for a stretch-activated sensor (Lehtonen and Kinnunen, 1995). 

Cifuentes, M.E., Delaney, T., and Rebecchi, M.J., 1994, D-rayo-Inositol 1,4,5-trisphosphate inhibits binding of phospholipase C-delta 1 to bilayer membranes. J. Biol. Chem. 269 1945-1948. 

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