Cerebroside

Product-ion ESI-MS spectra of protonated SM species only display a fragment ion at m/z 184, corresponding to phosphocholine, after low-energy CID. The low-abundant fragment ions, corresponding to the loss of fatty acids present in the product-ion spectra of protonated PC species, are absent in the case of SM species. This is due to a fact that the amide bond in SM species is more stable than the ester bond in PC species. 

SM species can readily form anion adducts in the negative-ion mode. Product-ion ESI-MS spectra of anion adducts of SM species after low-energy CID only display a [M-15] fragment ion, corresponding to the loss of a methyl group [14]. 

In the positive-ion mode, cerebroside (HexCer) species including both GluCer and GalCer can be readily ionized as their proton or alkaline adducts (i.e., [M-I-XJ+, X=H, 

depending on the availability and affinity of the small cation(s) [12, 16, 17]. The fragmentation pattern of alkaline-adducted HexCer species yield three types 

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CiaH3 7N02,CH3-[CH2],2-CH CH.CH(0H). CH(NH2>-CH20H. a base, forming part of the molecules of sphingomyelins and the cerebrosides, from which it splits off on hydrolysis. It crystallizes in needles from ether. 

Cerebrosides are found in the brain and in the myelin sheath of nerve tissue The structure of the cerebroside phrenosine is... 

FIGURE 8.13 The structure of a cerebroside. Note the sphiugosiue backbone. 

Component of the myelin sheath surrounding the axons of nerve cells. Additional compounds of the myelin sheath are phospholipids, cholesterol, cerebrosides, and specific keratins. The myelin sheath constitutes an isolating barrier during electrophysiological axonal signaling. 

The glycosphingolipids (GSLs) are sugar-containing lipids built on a backbone of ceramide they include galactosyl- and glucosylceramide (cerebrosides) and the gangliosides. Their structures are described in Chapter 14. They are mainly located in the plasma membranes of cells. 

Cerebrosides, snlfatides, gangliosides, and other glycolipids appear as yellow spots cholesterol appears as a light red spot... 

Sphingolipids (ceramids, sphingomyelin, cerebrosides, sulfatides, gangliosides) and lipids with secondary amines produce blue spots on a white backgound (CAUTION benzidine is a carcinogen)... 

Phosphatidyl Glycerol Phosphatidyl Inositol Cerebrosides Gangliosides... 

D-Galactose H HO HO H HOH2 C—C—C—C—C—CHO HO H H HO widespread in plants lactose ovomucoid cerebrosides albumin gland of snail frog and toad spawn beef lung... 

Because membranes components participate in nearly every cell activity their structures are also dynamic and far from the equilibrium states that are most readily understood in biophysical terms. Newly synthesized bilayer lipids are initially associated with endoplasmic reticulum (Ch.3) whereas phospholipids initially insert into the cytoplasmic leaflet while cholesterol and sphingolipids insert into the luminal endoplasmic reticulum (ER) leaflet. Glycosylation of ceramides occurs as they transit the Golgi compartments, forming cerebrosides and gangliosides in the luminal leaflet. Thus, unlike model systems, the leaflets of ER membranes are asymmetric by virtue of their mode of biosynthesis. 

Central nervous system myelin is enriched in certain lipids. Table 4-1 lists the composition of bovine, rat, and human myelin compared to bovine and human white matter, human gray matter, and rat whole brain [1] (see Ch. 3). While there are no absolutely myelin-specific lipids, cerebroside (galactosyl ceramide) is the most typical of myelin. With the exception of early development,... 

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