Lipid, analysis water activity

Conductivity, in water activity measurement, 67-70 Confocal laser scanning microscopy to characterize lipid crystals, 575-579 description of, 575, 577 Conjugated dienes and trienes, determination of, 515-517 Conjugated linoleic acid (CLA), fatty acid analysis, 437-438, 445-446 Convection oven, gravimetric measurement of water, 7-8, 10-11... 

Cubic phases are also unique in their ability to accommodate proteins as compared to other lipid-water phases. A wide range of globular proteins with molecular weights 5,000-150,000 are known to form cubic phases when mixed with lipids and water. So far few single ternary lipid-protein-water phase diagrams have been completely determined [7], [13] one system that has been looked at is that of monoolein-water-lysoz5one. Protein incorporation results in increased water swelling, and all three phases, Cp, Cd and CG/ occur. The protein molecules are located in the water channel systems and retain their native structure. This has been proved by thermal analysis of the phase, and measurements of enzymatic activity [7]. 

Lipid extraction and analysis — Skin specimens were homogenized in distilled water and precipitated with 10% perchloric acid. The precipitates were washed with 2% perchloric acid and distilled water and then extracted twice with chloroform-methanol (2 1 v/v). Extracts were pooled and analysed by chromatography on precoated thin layer plates (20 x 20 cm) of silica gel 60 (Merck, A.G. Darmstadt, Germany) after activation at 110 °C for 30 minutes. Lipid analysis was performed as described by Summerly and Woodbury". Plates were developed firstly in hexane-benzene (1 1, v/v) and secondly in the same dimension with petroleum ether (b.p. 60-80 °C)-diethyl ether-acetic acid (80 20 1, by vol). 

Second, P-gp differs from other transporters in that it recognizes its substrates when dissolved in the lipid membrane [52], and not when dissolved in aqueous solution. The site of recognition and binding has been shown to be located in the membrane leaflet facing the cytosol [53, 54], This implies that the membrane concentration of the substrate, Csm, determines activation [57]. Since the nature of a molecular interaction is strongly influenced by the solvent, the lipid membrane must be taken into account as the solvent for the SAR analysis of P-gp. Under certain conditions, the effect of additional solvents or excipients (used to apply hydrophobic substrates or inhibitors) on the lipid membrane and/or on the transporter must also be considered. Lipophilicity of substrates has long been known to play an important role in P-gp-substrate interactions nevertheless, the correlation of the octanol/water partition coefficients with the concentration of half-maximum... 

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

Petunia leaves are typically coated with a sticky exudate, and it was of interest to determine if this exudate contained any of the insect-inhibitory steroids. We subjected fresh leaves to an initial five minute soak in water followed by a one minute dip in chloroform with gentle agitation. This chloroform extract contained nonpolar surface lipids and substances tentatively identified as carbohydrate esters (ca 1 % of fresh wt.), but no biologically active materials were shown to be present by HPLC analysis. Further workup of the solvent-washed leaves by grinding with additional chloroform then yielded the usual quantities of active materials, showing that the insect-inhibitory components were definitely neither part of the exudate nor of the leaf surface coating. 

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