Bonds acyl phosphate

Allylic phosphates are used for carbonylation in the presence of amines under pressure. Carbonylation of diethyl neryl phosphate (389) affords ethyl homonerate (390), maintaining the geometric integrity of the double bond[244]. The carbonylation of allyl phosphate in the presence of the imine 392 affords the /3-lactam 393. The reaction may be explained by the formation of the ketene 391 from the acyl phosphate, and its stereoselective (2 + 2] cycloaddition to the imine 392 to give the /3-lactam 393(247],... 

Closely related to the carboxylic acids and nitriles discussed in the previous chapter are the carboxylic acid derivatives, compounds in which an acyl group is bonded to an electronegative atom or substituent that can net as a leaving group in a substitution reaction. Many kinds of acid derivatives are known, but we ll be concerned primarily with four of the more common ones acid halides, acid anhydrides, esters, and amides. Esters and amides are common in both laboratory and biological chemistry, while acid halides and acid anhydrides are used only in the laboratory. Thioesters and acyl phosphates are encountered primarily in biological chemistry. Note the structural similarity between acid anhydrides and acy) phosphates. 

Acyl phosphate (Section 21.8) A functional group with an acyl group bonded to a phosphate, RC02P032- or RC02P03R -. 

An enzymatic reaction intermediate formed by phospho-ryl transfer to a carboxyl group on an enzyme. Acyl-phosphates are structurally analogous to acid anhydrides (R—CO —O —CO—R ), and they are thermodynamically less stable than either of the two phosphoanhydride bonds in ATP. This is evident by the fact that the acetate kinase reaction (ADP + acetyl-phosphate = ATP + acetate) favors ATP formation with an equilibrium constant of about 3,000. Acetyl-phosphate can be chemically synthesized by reacting orthophosphate with acetic anhydride. 

The initial concentrations of (ECa) and (EGTA) are usually v 10 pM and 5 mM, respectively. Under these conditions 12 kJ/mol become available when one mol of calcium ions is removed from the protein. This is scarcely sufficient for the formation of a sizeable fraction of a phosphoenzyme with an acyl phosphate bond. 

Another three-carbon compound, 1,3-bisphospho-glycerate (Fig. 13—4), contains an anhydride bond between the carboxyl group at C-l and phosphoric acid. Hydrolysis of this acyl phosphate is accompanied by a large, negative, standard free-energy change (AG ° =... 

In Lipmann s original scheme group Y was visualized as adding to a carbon-carbon double bond to initiate the sequence. Isotopic exchange reactions ruled out the possibility that either ADP or P might serve as Y, but it was attractive to think that a bound phosphate ion, e.g., in a phospholipid or coenzyme, could be involved. Y B of Fig. 18-12 would be similar in reactivity to an acyl phosphate or thio-ester. However, whatever the nature of Y B, part of group Y would be left attached to B after the transfer of Y to X. For example, if Y were Y OH... 

The active site for this reaction lies in a domain formed by the aminoterminal third of CPS. This domain forms a structure, called an ATP-grasp fold, that surrounds ATP and holds it in an orientation suitable for nucleophilic attack at the Y phosphoryl group. Proteins containing ATP-grasp folds catalyze the formation of carbon-nitrogen bonds through acyl-phosphate intermediates and are widely used in nucleotide biosynthesis. In the final step catalyzed by carbamoyl phosphate synthetase, carbamic acid is phosphorylated by another molecule of ATP to form carbamoyl phosphate. 

For example, a number of studies have been made on the metal ion-catalyzed hydrolyses of acetyl phosphate and acetyl phenyl phosphate, " but the role of the metal ion in these processes remains uncertain. Investigations of catalysis by exchange labile metal ions e.g. Ca" and Mg") have yielded conflicting results and both the nature and distribution of the kinetically significant species, as well as the positions of bond cleavage, have yet to be determined unequivocally. Chelation, charge neutralization and attack by metal-bound hydroxide have variously been proposed as important factors in acyl phosphate hydrolysis. 

Glutathione (8.20) y-glutamylcysteinylglycine, is biosynthesised in a stepwise manner from the A -terminus but not by the ribosomal route. Instead, each peptide bond is formed under the control of a specific enzyme, glutamyl-cysteine synthetase and glutathione synthetase, respectively, with ATP as a substrate to form an acyl phosphate as an unsymmetrical anhydride. Reduced glutathione (GSH) with a thiol... 

The hydrolytic lability of the phosphoenzyme intermediate prevented its isolation in an active form however, the P-labeled phosphoenzyme could be isolated in good yield in a denatured form by precipitation of the protein with acid at low temperature in the presence of a P-labeled substrate 74). Further chemical analysis indicated that the intermediate is an acyl phosphate, with the phosphoryl group bonded to an enzymic carboxyl group (76). 

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