Phosphatidylserine , metabolic roles

Pyridoxal phosphate has a clear role in lipid metabolism as the coenzyme for the decarboxylation of phosphatidylserine, leading to the formation of phosphatidylethanolamine, and then phosphatidylcholine (Section 14.2.1), and membrane lipids from vitamin Bg-deficient animals are low in phosphatidylcholine (She et al., 1995). It also has a role, less well defined, in the metabolism of polyunsaturated fatty acids vitamin Bg deficiency results in reduced activity of A desaturase and impairs the synthesis of eicosapentanoic and docosahexanoic acids (Tsuge et al., 2000). 

The simplest topic covered in this chapter is that of choline, a compound with a 2-carbon backbone, which occurs in the diet and in the body mainly in the form of the structural lipid phosphatidylcholine. Choline is an issue in the metabolism of other lipids, namely, of phosphatidylserine, phosphatidylethanola-mine, and sphingomyelin. Phosphatidylino-sitol is a lipid that has received enormous attention from cell biologists because of its role in transmitting signals within the cell. Sphingomyelin is a structmal lipid in the plasma membrane, but it has received increased attention because of its role in regulating the growth, differentiation, and death of cells. 

Pyruvoyl cofactor is derived from the posttranslational modification of an internal amino acid residue, and it does not equilibrate with exogenous pyruvate. Enzymes that possess this cofactor play an important role in the metabolism of biologically important amines from bacterial and eukaryotic sources. These enzymes include aspartate decarboxylase, arginine decarboxylase," phosphatidylserine decarboxylase, . S-adenosylmethionine decarboxylase, histidine decarboxylase, glycine reductase, and proline reductase. ... 

Phosphatidylinositol is uncommon in bacteria and is found in a few Gram-positive species only. In actinomycetes and a few other bacteria mannosides of phosphatidylinositol may be present. Other glycerophospholipids such as phosphatidic acid and phosphatidylserine have a widespread occurrence in bacteria but only in small amounts. Both of these lipids play an important role as metabolic intermediates (Finnerty, 1978 Raetz, 1978). 

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