Lipids have not traditionally been considered likely candidates for catalyzing reactions in biological systems. However, there is significant evidence that aggregates of amphiphilic compounds are capable of catalyzing reactions in synthetic organic chemistry. Here we demonstrate the potential for the hydrophobic region of a lipid bilayer to provide an environment suitable for catalysis by means of a lipozyme, or lipid aggregate capable of speeding up a chemical reaction. By bringing organic molecules into the non-polar or hydrophobic region of a lipid bilayer, reactions can be catalyzed by collections of small, nonpolar or amphiphilic molecules. We demonstrate this concept by the ester hydrolysis of calcein-AM to produce a fluorescent product, which is a widely used assay for esterase activity in cells. The reaction was first carried out in a two phase octanol-water system with the organic phase containing the cationic amphiphiles cetyltrimethylammonium bromide (CTAB) or octadecylamine. The octanol was then replaced with DOPC added to the water in the form of vesicles, where the reaction was also found to be carried out. The reaction was monitored using quantitative fluorescence which revealed catalytic turnover numbers on a scale of 10−4s−1 for each system, which is comparable to some slow enzymes. The reaction product was characterized by 1H-NMR measurements which were consistent with ester hydrolysis. The implications of thinking about lipid aggregates as catalytic entities are discussed in the context of biochemistry, pharmacology and synthetic biology.

The fine structure of Apricot pectin polysaccharides is discussed from both literature and recent work we have performed. Structural characterization utilized 1D and 2D homo- and hetero-nuclear NMR spectroscopy including results from High Performance Size Exclusion Chromatography (HP-SEC), HP Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD) and FTIR spectroscopy. The purified pectin fraction (F1AP) was found to be composed of D-galacturonic acid, L-rhamnose, D-arabinose and D-galactose in a 1.0 : 0.1 : 0.36 : 0.12 molar ratio, respectively, which is consistent with a pectin RG-1 branched with arabinogalactan side chain polysaccharides, and has a weight-average molecular weight of approximately 1588.2 kDa. The slope of the hydrodynamic radius versus the molar mass was 0.57, indicating the presence of coil conformations. The results from HPAEC-PAD, HPSEC and NMR spectroscopy (1H, 13C, zTOCSY, HSQC, HSQCTOXY and HMBC) demonstrated that F1AP fine fraction F1AP1, derived from original F1AP, has a backbone of (1→4)-linked -D-galacturonic acid and -L-rhamnopyranosyl residues branched with arabinogalactan of multiply glycosidic linkages of T- α-Araf, 3-α-Araf, 5-α-Araf, T- α -Arap, 2- α-Arap side chains, having methyl and acetylated groups, and has high molecular weights (1945 kDa). While the other F1A6 fraction consists predominately of an HG region of pectin polysaccharides with low molecular weights (117.5 kDa), less aggregated. The F1AP1 polysaccharide was highly viscous and its hydrodynamic radius was 64,3 nm. The exponent b of Rh-Mw (conformation plot) was determined to be 0.48, indicating a compact flexible coil conformation of the macromolecule in solution. However, the F1AP6 fraction of apricot fruits belong to backbone of repeats units of [-(1→4)-α-D-GalpA-1]n – both HG and partly contents RG-II polysaccharides, bearing heterosugar sidechains, including α-Ara, α -Rha and β-Gal residues and adopt more stiffness rod like conformation.