Acyl phosphates phosphorylation

The most important type of acid anhydride in biochemistry is that between two molecules of phosphoric acid, as exemplified by the two terminal bonds of ATP (p. 67), but the pyrophosphate bond is not the only type of energy-rich bond as can be seen from Table XI. Mixed anhydrides of carboxylic and phosphoric acids (acyl-phosphates), phosphorylated enol groups (enolphosphates), phosphorylated guanidine groups (guanidine phosphates), compounds of sulphhydryl groups with phosphoric or carboxylic acids (thioesters or thiophosphates), all these types of compound are energy-rich. 

Like all anhydrides (Section 21.5), the mixed carboxylic-phosphoric anhydride is a reactive substrate in nucleophilic acyl (or phosphoryl) substitution reactions. Reaction of 1,3-bisphosphoglycerate with ADR occurs in step 7 by substitution on phosphorus, resulting in transfer of a phosphate group to ADP and giving ATP plus 3-phosphoglycerate. The process is catalyzed by phospho-gjvcerate kinase and requires Mg2+ as cofactor. Together, steps 6 and 7 accomplish the oxidation of an aldehyde to a carboxylic acid. 

The Ca transport ATPase of the surface membrane is a Ca -calmodulin-dependent enzyme of approximately 138-kDa mass that is structurally distinct from the sarcoplasmic reticulum Ca -ATPase, but shares with it some similarities in the mechanism of Ca translocation [2,3,34]. In both enzymes the Ca -dependent phosphorylation of an aspartyl-carboxyl-group by ATP leads to the formation of an acyl phosphate intermediate that provides the coupling between ATP hydrolysis and Ca translocation. 

When we investigate this substrate-level phosphorylation reaction in detail, we find it also involves a molecule of phosphate. Phosphate reacts initially with succinyl-CoA, converting the thioester into an acyl phosphate, which is, of course, a mixed anhydride (see Box 7.27). It is actually hydrolysis... 

This phosphotransferase [EC 2.7.2.1] catalyzes the thermodynamically favored phosphorylation of ADP to form ATP Aeq = [ATP][acetate]/ [acetyl phosphate] [ADP] = 3000). GDP is also an effective phosphoryl group acceptor. This enzyme is easily cold-denatured, and one must use glycerol to maintain full catalytic activity. Initial kinetic evidence, as well as borohydride reduction experiments, suggested the formation of an enzyme-bound acyl-phosphate intermediate, but later kinetic and stereochemicaT data indicate that the kinetic mechanism is sequential and that there is direct in-line phosphoryl transfer. Incidental generation of a metaphosphate anion during catalysis may explain the formation of an enzyme-bound acyl-phosphate. Acetate kinase is ideally suited for the regeneration of ATP or GTP from ADP or GDP, respectively. 

This enzyme [EC 2.7.1.61] catalyzes the reaction of an acyl phosphate with a hexose to produce an acid and hexose phosphate. If the sugar is D-glucose or D-man-nose, phosphorylation is on 06. If the sugar is D-fructose, phosphorylation is on 01 or 06. 

Acyl-phosphates can participate in so-called in-line phosphoryl transfer reactions, and depending on reaction conditions, acyl-phosphate compounds can form a metaphosphate anion ... 

Acyl-phosphates also display an unusual U -shaped pH profile for the rate of hydrolysis (see Fig. 1). This reflects the fact that acyl-phosphate compounds are susceptible to both acid- and base-catalyzed hydrolysis, and the shoulder at less acidic pH values reflects the slightly faster hydrolysis of the monoanion, compared to the dianion. Observation of a U -shape pH-rate profile for a previously uncharacterized phosphoryl-enzyme intermediate supports the inference that an acyl-phosphate has formed. 

A corresponding reaction of acetate ion with AJP is also catalyzed by a bivalent metal ion. The reaction probably results in the formation of an acyl phosphate, which has not been identified as such but has been identified by trapping of the product with hydroxylamine. The best catalyst is beryllium ion, which catalyzes optimally at molar ratios of 1 to 1 or less. Acetate ion is presumably the reactive species, since the pH optimum of the reaction is 5. It is concluded from the pH effects in this study and in the transphosphorylation reaction that a complex of the metal ion and nucleophile must occur. Since acetate ion is a monodentate ligand, the mechanism postulated for the phosphorylation reaction above cannot be completely applicable to this case (36). 

Napper, S. Delbaere, L.T.J. Waygood, E.B. The aspartyl replacement of the active site histidine in histidine-containing protein, HPr, of the Escherichia coli phosphoenolpyruvate sugar phosphotransferase system can accept and donate a phosphoryl group. Spontaneous dephosphorylation of acyl-phosphate autocatalyzes an internal cyclization. J. Biol. Chem., 274, 21776-21782 (1999)... 

Once orotate is formed, the ribose 5-phosphate side chain, provided once again by PRPP, is attached to yield orotidylate (Fig. 22-36). Orotidylate is then decarboxy-lated to uridylate, which is phosphorylated to UTP. CTP is formed from UTP by the action of cytidylate synthetase, by way of an acyl phosphate intermediate (consuming one ATP). The nitrogen donor is normally glutamine, although the cytidylate synthetases in many species can use NH4 directly. 

The problem of oxidative phosphorylation has been approached through model studies that utilize the phosphorylating potential of metaphosphate. In the mitrochondrial process inorganic phosphate and adenosine diphosphate are converted to adenosine triphosphate. Wieland, in a series of papers (e.g. ref. 31), has shown that a variety of thiolactones can activate inorganic phosphate in the presence of bromine for transfer to adenosine diphosphate (ADP). The intermediate may be an acyl phosphate or a sulfonium salt similar to that postulated by Higuchi and Gensch32 and by Lambeth and Lardy33, viz. 

The detection of minor amounts of monobenzyl phosphate, which presumably arise from hydrolysis of the monobenzyl acyl phosphate, is an example of the intramolecular migration of monoalkyl hydrogen phosphate. This process resembles the acid-catalyzed migration of a phosphoryl moiety adjacent to a vicinal hydroxyl function128-130, viz. 

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