Phosphocholine head group

It should be noted here that the synthesis of sphingomyelin, the lipid whose synthesis and breakdown are most intricately involved in the process of apoptosis, is dependent on the presence of PC, since the final step in SM synthesis involves the exchange of the phosphocholine head group from PC to ceramide (see Eigure 1). Theoretically, therefore, inhibition of PC synthesis may lead to an inhibition of SM generation and an accumulation of pro-apoptotic ceramides. On the other hand, an increased breakdown of SM by SMases as frequently observed in apoptotic cells, was shown to increase the conversion of PC to anti-apoptotic DAG (Sillence and Allan, 1998, for anti-apoptotic action of DAG see below). 

Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following membrane lipids, name the components that serve as the hydrophobic and hydrophilic units (a) phos-phatidylethanolamine (b) sphingomyelin (c) galactosyl-cerebroside (d) ganglioside (e) cholesterol. 

D3g-dodecylphosphocholine (DPC) micelles were used to provide a lipid environment. This molecule, which possesses a phosphocholine head group and a single Ci2 hydrocarbon chain, mimics the phospholipid component of lipoprotein surface monolayers. About 40 DPC molecules form a micelle which has molecular weight of about 16 kDa. Thus, the apoLp-IH/DPC (1 1 protein/micelle) complex... 

Both PC and SM contain a phosphocholine head group, which makes the molecules zwitterionic and largely dictates their ionization and fragmentation behavior. PC and SM readily form [M+H]+ ions which upon CAD yield an abundant phosphocholine fragment with m/z 184 (cf. Table 1) and can thus be selectively detected by scanning for parents of this ion. In the presence of different salts, PC and SM form both cation and anion adducts, which may be utilized for the elucidation of the fatty acids present in the molecules [19,29,34,44,45]. In case of SM, also a fragment indicative of the long-chain base is found [45]. 

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