Phosphate esters, biosynthesis

Phosphatidates (anions of the phosphatidic acids), the simplest phospholipids, are phosphate esters of diacylglycerol. They are important intermediates in the biosynthesis of fats and phospholipids (see p. 170). Phosphatidates can also be released from phospholipids by phospholipases. 

Acid dye method for the analysis of thiamin, 18A, 73 electrophoretic separation and fluorometric determination of thiamin and its phosphate esters, 18A, 91 catalytic polarography in the study of the reactions of thiamin and thiamin derivatives, 18A, 93 preparation of thiamin derivatives and analogs, 18A, 141 preparation of the mono- and pyrophosphate esters of 2-methyl-4-amino-5-hydroxymethylpyrimidine for thiamin biosynthesis, 18A, 162 formation of the pyrophosphate ester of 2-methyl-4-amino-5-hydroxymethylpyrimidine by enzymes from brewers yeast in thiamin biosynthesis, 18A, 203 resolution, reconstitution, and other methods for the study of binding of thiamin pyrophos-... 

Elimination usually involves loss of a proton together with a nucleophilic group such as -OH, -NH3+, phosphate, or pyrophosphate. However, as in Eq. 13-18, step c, electrophilic groups such as -COO-can replace the proton. Another example is the conversion of mevalonic acid-5-pyrophosphate to isopentenyl pyrophosphate (Eq. 13-19) This is a key reaction in the biosynthesis of isoprenoid compounds such as cholesterol and vitamin A (Chapter 22). The phosphate ester formed in step a is a probable intermediate and the reaction probably involves a carbo-cationic intermediate generated by the loss of phosphate prior to the decarboxylation. 

Among activated forms of amino acids, mixed anhydrides with inorganic phosphate or phosphate esters require a special discussion because they are universally involved in peptide biosynthesis through the ribosomal and non-ribosomal pathways. These mixed anhydrides have stimulated studies in prebiotic chemistry very early in the history of this field. Amino acyl adenylates 18c have been shown to polymerize in solution [159,160] and in the presence of clays [139]. However, their participation as major activated amino acid species to the prebiotic formation of peptides from amino acids is unlikely for at least two reasons. Firstly, amino acid adenylates that have a significant lifetime in aqueous solution become very unstable as soon as either CO2 or bicarbonate is present at millimolar concentration [137]. Lacey and coworkers [161] were therefore conduced to consider that CO2 was absent in the primitive atmosphere for aminoacyl adenylate to have a sufficient lifetime and then to allow for the emergence of the modern process of amino acid activation and of the translation apparatus. But this proposition is unlikely, as shown by the analysis of geological records in favor of CO2 contents in the atmosphere higher than present levels [128]. It is also in contradiction with most studies of the evolution of the atmosphere of telluric planets [30,32], Secondly, there is no prebiotic pathway available for adenylate formation and ATP proved to be inefficient in this reaction [162]. 

When such strains as E. coli 83-24, which are blocked after shikimic acid, were grown on minimal medium plus aromatic supplement, they accumulated 400-800 mg. of shikimic acid per liter, together with variable amounts of shikimate 5-phosphate. Since no mutants that are blocked between shikimic acid and its phosphorylated form were found, it was considered that the phosphate ester is not on the main path of biosynthesis. As will be pointed out later, enzymic studies showed that shikimate 5-phosphate is actually an intermediate between shikimate and the aromatic compounds. It would appear, therefore, that the block in such strains as E. coli 83-24 is probably immediately after shikimate 5-phosphate. With filtrates from this organism, methods were developed for the isolation of pure shikimate and for its stepwise degradation. ... 

While the biosynthesis of phosphate esters is common in intermediary metabolism, the conjugation of foreign compounds with phosphate is encountered only rarely in vertebrate species (3,7,28). Indeed, to date, insects appear to be the only major group of organisms that utilize this pathway to any significant extent in the metabolism of foreign compounds (3,6,7). 

The biosynthesis of threonine from aspartate involves formation of the four metabolic intermediates illustrated in Fig. 2. The /3-carboxyl group of aspartate is first activated by formation of an acylphosphate, and this reaction is followed by two reductive steps resulting in the synthesis of homoserine. After formation of a C4 phosphate ester of homoserine, threonine is synthesized by a complex rearrangement which entails formation of the terminal methyl group and transfer of the oxygen atom from C-4 to form a hydroxyl group at C-3. 

Metabolism employs phosphorus compounds in many ways. Phosphate esters are central to information storage, serve as the currency for energy exchange, and contribute to membrane fluidity. They are important intermediates in carbohydrate metabolism, in formation of nucleotides and their assembly into RNA and DNA, and in steroid fabrication and protein lipidation through the isoprenoid biosynthesis pathways. They hold key roles in cell signaling processes, including G-protein... 

Although the P content of natural wood is very low, some phosphate esters are presumably present since they are involved in the biosynthesis of lignin. Wood ash is comparatively rich in the two fertilizer elements, phosphorus and potassium ... 

Dolichol is related to vitamin A (10.66a), the phosphate ester of which may also be involved in glycosyl transfer reactions in the body (Chapter 11). Polyprenol pyrophosphates are involved in the biosynthesis of rubber, gutta-percha and other terpenes (Chapter 11.5). 

Acyl carrier protein, ACP a small, acidic, heat-stable globular protein which is part of the fatty acid synthesizing complex in . coli and other bacteria, yeast and plants. It carries the fatty acid chain during biosynthesis of the latter. The ACP from E. coii contains 77 amino acids (M, 8,847), and the primary structure is known. Sulfiir-containing amino adds are absent, but a molecule of phosphopantetheine (which possesses -SH) is linked to the protein via a phosphate ester to the hydroxyl of serine 36. All ac l residues formed during fatty acid biosynthesis are bound as thioesters to the SH of this prosthetic group. The M, of isolated ACP lie between 8,600 (Clostridium butyrkum) and 16,000 (yeast). 

Xanthosine phosphates phosphate esters of xanthosine, or xanthine nucleotides Xanthosine S"-monophosphate, XMP, xandudylU mid, xanthylic acid, M, 364.22 is an intermediate of Pu e biosynthesis (see). 

An example of elimination from such a phosphate ester, important in the biosynthesis of aromatic amino acids (Chapter 12), involves not only the loss of water but also the simultaneous migration of a carbon-carbon double bond. This kind of elimination is referred to as conjugate elimination (or 1,4-eUmination). 

The conversion of histidinol phosphate to histidine requires removal of the phosphate group free histidinol was the first precursor of histidine established in genetic studies. The hydrolysis of histidinol phosphate is catalyzed by a phosphatase that has recently been purified by Ames from Neurospora extracts. This enzyme is active with histidinol phosphate as a substrate, but has very little, if any, activity with a number of phosphate esters, including the other imidazole compounds involved in histidine biosynthesis. At least one less specific phosphatase occurs in Neurospora histidinol phosphate is also hydrolyzed nonspecifically, but the activity of the nonspecific hydrolytic enzyme is slow compared with the specific histidinol phosphatase. The nonspecific reaction may account for the slow growth of mutants deficient in the specific enzyme. The specific enzyme is quite insensitive to beryllium and chelating agents, which inhibit nonspecific phosphate hydrolysis. 

In addition two compounds which appear to be the phosphate esters of I and II have also been obtained. These results have led Ames and C 0-workers to postulate a scheme for the biosynthesis of histidine in which the phosphate esters of I, 11, and III were assumed to be the direct sequential intermediates of histidine from an unknown carbohydrate. The occurrence of a trihydroxypropyl side chain in the first compound in... 

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