Nonenzymatic synthesis of glycerolipids catalyzed by imidazole

Biomimetic construction of phospholipid membranes by direct aminolysis ligations

Construction of artificial cells requires the development of straightforward methods for mimicking natural phospholipid membrane formation. Here we describe the use of direct aminolysis ligations to spontaneously generate biomimetic phospholipid membranes from water-soluble starting materials. Additionally, we explore the suitability of such biomimetic approaches for driving the in situ formation of native phospholipid membranes. Our studies suggest that non-enzymatic ligation reactions could have been important for the synthesis of phospholipid-like membranes during the origin of life, and might be harnessed as simplified methods to enable the generation of lipid compartments in artificial cells.

Cholinesterase-like organocatalysis by imidazole and imidazole-bearing molecules

Organocatalysis, which is mostly explored for its new potential industrial applications, also represents a chemical event involved in endogenous processes. In the present study, we provide the first evidence that imidazole and imidazole derivatives have cholinesterase-like properties since they can accelerate the hydrolysis of acetylthiocholine and propionylthiocholine in a concentration-dependent manner. The natural imidazole-containing molecules as L-histidine and histamine show a catalytic activity, comparable to that of imidazole itself, whereas synthetic molecules, as cimetidine and clonidine, were less active. In the experimental conditions used, the reaction progress curves were sigmoidal and the rational of such unexpected behavior as well as the mechanism of catalysis is discussed. Although indirectly, findings of the present study suggests that imidazolic compounds may interfere with the homeostasis of the cholinergic system in vivo.

Discovery and characterization of an Arabidopsis thaliana N-acylphosphatidylethanolamine synthase

N-Acylethanolamines (NAEs) are lipids involved in several physiological processes in animal and plant cells. In brain, NAEs are ligands of endocannabinoid receptors, which modulate various signaling pathways. In plant, NAEs regulate seed germination and root development, and they are involved in plant defense against pathogen attack. This signaling activity is started by an enzyme called N-acylphosphatidylethanolamine (NAPE) synthase. This catalyzes the N-acylation of phosphatidylethanolamine to form NAPE, which is most likely hydrolyzed by phospholipase D beta/gamma isoforms to generate NAE. This compound is further catabolized by fatty amide hydrolase. The genes encoding the enzymes involved in NAE metabolism are well characterized except for the NAPE synthase gene(s). By heterologous expression in Escherichia coli and overexpression in plants, we characterized an acyltransferase from Arabidopsis thaliana (At1g78690p) catalyzing the synthesis of lipids identified as NAPEs (two-dimensional TLC, phospholipase D hydrolysis assay, and electrospray ionization-tandem mass spectrometry analyses). The ability of free fatty acid and acyl-CoA to be used as acyl donor was compared in vitro with E. coli membranes and purified enzyme (obtained by immobilized metal ion affinity chromatography). In both cases, NAPE was synthesized only in the presence of acyl-CoA. beta-Glucuronidase promoter experiments revealed a strong expression in roots and young tissues of plants. Using yellow fluorescent protein fusion, we showed that the NAPE synthase is located in the plasmalemma of plant cells.

Mass spectrometric identification of molecular species of phosphatidylcholine and lysophosphatidylcholine extracted from shark liver

The profile and structural characterization of molecular species of phosphatidylcholine (PC) and lysophosphatidylcholine (LysoPC) from shark liver using liquid chromatographic/electrospray ionization mass spectrometry (LC-ESI/MS) and tandem mass spectrometry (MS/MS) are described for the first time in this paper. The presence of (i) a relatively high content of ether PC species, such as 1-O-alkyl- and 1-alk-1'-enyl-2-polyunsaturated PC species (about 20%), and (ii) a high percentage of docosahexaenoic acid (DHA)-containing LysoPC (about 27%) is the characteristic of this marine material. 1-Hexadecanoyl-2-docosahexaenoyl-PC (16:0/22:6; about 24%) and 1-docosahexaenoyl-2-hydroxyl-LysoPC (22:6; about 27%) are the two most abundant species in shark liver. The other polyunsaturated PC species including ether PC are tentatively identified as 1-heptadecanoyl-2-docosahexaenoyl-PC (17:0/22:6), 1-octadecyl-2-docosahexaenoyl-PC (alkyl-18:0/22:6), 1-hexadecyl-2-docosahexaenoyl-PC (alkyl-16:0/22:6), 1-octadecenyl-2-eicosapentaenoyl-PC (alkyl-18:1/20:5), 1-octadecenyl-2-eicosatetraenoyl-PC (alkyl-18:1/20:4), 1-hexadecyl-2-docosapentaenoyl-PC (alkyl-16:0/22:5), 1-(1 Z-hexadecenyl)-2-docosahexaenoyl-PC (alkenyl-16:0/22:6), and 1-octadecenoyl-2-docosahexaenoyl-PC (18:1/22:6). These results establish that high contents of ether DHA-PC and DHA-LysoPC species can be obtained from shark liver.