Organic serine phosphate groups

Phospholipid Polar lipids containing a diglyceride and a phosphate group bound to different organic compounds such as choline, ethanolamine, serine, and inositol. Phospholipids play a major role in cell membranes and act as emulsifiers in the food industry. Lecithin (phosphatidyl choline) is the most common phospholipid. 

Phospholipids containing phosphatidyl, inositol, lecithin, serine, and ethanolamine (Stevenson 1986) are the second most abundant identifiable form of organic P in the upper layer of the subsurface. These groups contain glycerol, fatty acids, and phosphate (Sims and Pierzjinski 2005). The P in the structure is a diester, which is more susceptible to degradation in soils than monoesters. 

Comprehensive Biological Catalysis—a Mechanistic Reference Volume has recently been published. The fiiU contents list (approximate number of references in parentheses) is as follows S-adenosylmethionine-dependent methyltransferases (110) prenyl transfer and the enzymes of terpenoid and steroid biosynthesis (330) glycosyl transfer (800) mechanism of folate-requiring enzymes in one-carbon metabohsm (260) hydride and alkyl group shifts in the reactions of aldehydes and ketones (150) phosphoenolpyruvate as an electrophile carboxyvinyl transfer reactions (140) physical organic chemistry of acyl transfer reactions (220) catalytic mechanisms of the aspartic proteinases (90) the serine proteinases (135) cysteine proteinases (350) zinc proteinases (200) esterases and lipases (160) reactions of carbon at the carbon dioxide level of oxidation (390) transfer of the POj group (230) phosphate diesterases and triesterases (160) ribozymes (70) catalysis of tRNA aminoacylation by class I and class II aminoacyl-tRNA synthetases (220) thio-disulfide exchange of divalent sulfirr (150) and sulfotransferases (50). 

Cysteine synthesis is a primary component of sulfur metabolism. The carbon skeleton of cysteine is derived from serine (Figure 14.7). In animals the sulfhydryl group is transferred from methionine by way of the intermediate molecule homocysteine. (Plants and some bacteria obtain the sulfhydryl group by reduction of SOj to S2 as H2S. A few organisms use H2S directly from the environment.) Both enzymes involved in the conversion of serine to cysteine (cystathionine synthase and y-cystathionase) require pyridoxal phosphate. 

Extension to insecticides of the idea that receptors could occur on enzymes was made soon after the end of the Second World War, when organic phosphates began to be used for their inhibition of AChase in insects. The hydroxy-group of serine in this enzyme was pinpointed as the receptor site for organophosphate insecticides (Section 13.3). 

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