Sphingomyelin chemistry

Other interfacial chemistries are found in juxtamem-brane domains of certain proteins that show a preferential interaction with specific lipids in their head group region. Important lipids involved in these interactions include the polyphosphate phosphatidylinositol lipids, cholesterol, gangliosides, and sphingomyelin. Interfacial chemistries play a role in the formation of microdomains and can determine the effective concentration of certain amphiphilic drugs in different membranes or even in different leaflets of the same membrane. 

The different varieties of orthophosphoric monoesters and diesters which are present in all living species are exceedingly numerous. Biologically important monoesters include the mononucleotides such as, for example, adenylic acid (adenosine monophosphate, AMP), inosinic acid, vitamin Bg and many phosphorylated proteins, for example, milk caseins. Biologically important diesters include the phospholipids (e.g. lecithin and phosphatidyl inositol), plasmalogens, sphingomyelins, cyclic nucleotide monophosphates (e.g. cyclic AMP), some teichoic acids, vitamin Bj2 and of course the immensely important nucleic acids (polynucleotides) (Chapters 10 and 11). The great stability of diesters is an essential feature of the chemistry of polynucleotides. 

Although our present knowledge of the chemistry and metabolism of sphingomyelin has not provided an answer to the pathogenesis of Niemann-Pick disease, the known facts will briefly be summarized with the hope that they will prepare the reader for further developments in the field of lipoidoses. 

The chemistry of ROS has been studied by several laboratories, and recently reviewed by Daemen (1973). Over 90% of the protein is rhodopsin, a photosensitive glycoprotein of molecular weight around 35,000, which is imbedded in a lipid bilayer. Phospholipids make up about 96% of the lipids of cattle ROS and cholesterol is the major component of the neutral lipid fraction. Phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) are the major phospholipids in all species examined, with phosphatidyl serine (PS), phosphatidyl inositol (PI), and sphingomyelin (SPh) present in lesser amounts (Anderson and Maude, 1972). Detailed analysis of the photoreceptor membranes of vertebrate species ranging from frogs to humans have revealed a fairly constant phospholipid class and protein composition (Basinger and Anderson, unpublished). 

Hannun, YA (1994) The sphingomyelin cycle and the second messenger function of ceramide. Journal of Biological Chemistry, 269, 3125-3128. 

Luherto, C, Yoo, DS, Suidan, HS, Bartoli, GM and Hannun, YA (2000) Differential effects of sphingomyelin hydrolysis and resynthesis on the activation of NF-kappa B in normal and SV40-transformed human fibroblasts. Journal of Biological Chemistry, 275,14760-14766. 

Okazaki, T, Bell, RM and Hannun, YA (1989) Sphingomyelin turnover induced by vitamin D3 in HL-60 cells. Role in cell differentiation. Journal of Biological Chemistry, 264, 19076-19080. 

Alkyl-2-acetyl-sn-glycerophosphorylcholine or "platelet-activating factor" (commonly abbreviated to PAF) is present in minute concentrations in platelets and certain other cells, yet exerts profound physiological effects. Its chemistry and biochemistry have been reviewed [353,866]. It is such a polar molecule that HPLC in the adsorption mode is required for its isolation. As the author and others [107,168] have reviewed these methods in some detail. It need only be mentioned here as an example that It elutes between sphingomyelin and lysophosphatidylcholine from a column of silica gel with a gradient of hexane-isopropanol-water in which the water content is increased [110]. No existing method is sufficiently sensitive to demonstrate the... 

Sphingomyelins are encountered in another aspect of clinical chemistry, that of lecithin-sphingomyelin ratios (qv). 

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