Lipids neutral, detection

With a better idea of how to identify possible isobars at a given m/z value, a better characterization of the ions detected can be accomplished. The identification of the PLs for the tissue section analyzed is described in Table 12.3. As can be seen, there is a DHB cluster ion detected at every mass isolated (typically arising from a neutral loss of 137, 154, 155, or 176). Many of the ions isolated for tandem MS show three and even four lipid species. The three primary lipid classes detected in the positive ion mode were PC, PS, and PE. Cerebrosides were also detected, but were present at a much lower intensity due to the conditions employed (18). The primary reason for maintaining an isolation width of 1.5 for most experiments was that PLs are considered fragile ions in ion trap analysis (26, 31) and thus can be lost during isolation if the isolation width is not wide enough. 

Figure 5 Drawing of a thin-layer chromatogram of the neutral lipids from an extract of the digestive gland-gonad (DGG) complex of Biomphalaria glabraia snails. The silica gel G plate was developed in the first direction in hexane-diethyl ether (80 20) and in the second direction in hexane-diethyl ether-methanol (70 20 10). Lipids were detected by spraying the plate with 50% H2SO4 and then charring it at 150"C for 5 min. Reproduced from Ref. 97 with the permission of Pergamon Press, Ltd.

It is commonly known that lipids, carbohydrates, and glycolipids are present in the Golgi apparatus (27). The determination of the components that react with the ZIO mixture was carried out by removing each component from tissues before incubation in the ZIO mixture. After lipid extraction by acetone (14), chloroform-methanol (15), or propylene oxide (27), no osmium-zinc precipitates could be detected in structures that normally reacted with ZIO. Blumcke et al. (15) summarized the nature of the lipids that react with the ZIO mixture as follows lipids and lipoproteins of cell membranes, neutral fat droplets (41), and lipid globules of type II pneumocytes and alveolar macrophages were, however, not as electron dense as the normally reactive lamellae containing highly unsaturated fatty acids. 

The range of values for this enzyme corresponds to 0.0 to 1.5 ml. A//20 sodium hydroxide required to neutralize the fat acids released by 1 ml. of serum under controlled conditions.18 Since 0.05 ml. of AV20 sodium hydroxide solution should be easily detectable, this corresponds to at least a 30-fold range and is in line with the large range in the blood lipids which is known to be inter-individual (p. 58). Because of lack of interest in the question, apparently no investigation has been made regarding the constancy or lack of constancy of the lipases in the blood of specific individuals. 

Once several silica gel column fractions have been collected, the eluted fractions must be analyzed for the presence of lipids. Thin-layer chromatography on silica gel plates will be introduced in this experiment for the detection and identification of neutral lipids. 

Actually, solid-phase extraction is used not only as a rough preliminary fractionation procedure. Prieto et al. described the complete fractionation of the total lipids from wheat into eight neutral lipid, two glycolipid, and four phospholipid classes in addition to PC and LPC, TV-acyl PE and A-acyl LPE were detected (37). However, two separate stationary phases (silica and aminopropyl) as well as seven different mobile phases were needed. Moreover, 14% crosscontamination of PC and LPC was observed, and the recovery of the phospholipids was limited to about 85%. Hence, SPE is a rapid and efficient technique for preliminary fractionation, but loses its advantages if more complex separations are tried. 

Wanasundara et al. (1999) reported that neutral lipids (acylglycerols and fatty acids) constitute 96% of the total lipid in flaxseed, whereas polar lipids (glycolipids and phospholipids) account for 1.4%. Stenberg et al. (2005) observed similar findings except that less phospholipid was detected. Froment et al. (1999) discussed the effects of cultivar, location, and late harvest on phospholipid content. Neutral lipid fraction of flaxseed meal was 95-98% triacylglycerols (TAG) and thus accounts for the predominant lipid in flaxseed (Oomah et al., 1996). 

Even though our understanding of the possible types of lipid-protein interactions in membranes has developed only recently, it was evident to early investigators that neutral solvents per se were the most effective for isolation purposes. Perhaps the most widely used solvent extraction procedure for many years was that employing a mixture of ethanol-diethyl ether (usually 1 3, v/v). This technique involved extraction of a tissue with this solvent combination for several hours at 55-60°C (Bloor, 1928). However, as more refined techniques were developed for the detection and assay of lipids, it became evident that this solvent (and condition) could have a deleterious... 

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