Aspartyl phosphate

FIGURE 10.10 The reaction of tridated sodium borohydride with the aspartyl phosphate at the active site of Na, K -ATPase. Acid hydrolysis of the enzyme following phosphorylation and sodium borohydride treatment yields a tripeptide containing serine, homoserine (derived from the aspartyl-phosphate), and lysine as shown. The site of phosphorylation is Asp" in the large cytoplasmic domain of the ATPase. 

Based on a series of studies of the effect of organic solvent on the reaction of Ca-ATPase with Pj and ATP synthesis, De Meis et al. proposed that a different solvent structure in the phosphate microenvironment in Ej and E2 forms the basis for existence of high- and low-energy forms of the aspartyl phosphate [93]. Acyl phosphates have relatively low free energy of hydrolysis when the activity of water is reduced, due to the change of solvation energy. The covalently bound phosphate may also reside in a hydrophobic environment in E2P of Na,K-ATPase since increased partition of Pj into the site is observed in presence of organic solvent [6] in the same manner as in Ca-ATPase. 

The ER takes up Ca2+ using a sarco(endo)plasmic reticulum ATPase (SERCA) pump (Figure 11.5), which has the same topology with 10 transmembrane domains and the same mechanism of action, with an aspartyl phosphate intermediate, as the PMCA pump described above. 

This enzyme [EC 1.2.1.11] catalyzes the reaction of aspartate-4-semialdehyde with orthophosphate and NADP+ to produce 4-aspartyl phosphate and NADPH. 

Probably the most common and widespread control mechanisms in cells are allosteric inhibition and allosteric activation. These mechanisms are incorporated into metabolic pathways in many ways, the most frequent being feedback inhibition. This occurs when an end product of a metabolic sequence accumulates and turns off one or more enzymes needed for its own formation. It is often the first enzyme unique to the specific biosynthetic pathway for the product that is inhibited. When a cell makes two or more isoenzymes, only one of them may be inhibited by a particular product. For example, in Fig. 11-1 product P inhibits just one of the two isoenzymes that catalyzes conversion of A to B the other is controlled by an enzyme modification reaction. In bacteria such as E. coli, three isoenzymes, which are labeled I, II, and III in Fig. 11-3, convert aspartate to (3-aspartyl phosphate, the precursor to the end products threonine, isoleucine, methionine, and lysine. Each product inhibits only one of the isoenzymes as shown in the figure. 

Aspartate a-decarboxylase 753, 755 Aspartate p-decarboxylase 746 Aspartate racemase 741 Aspartic acid (Asp, D) 52, 53s biosynthesis 517 pXa value of 293, 487 Aspartic proteases 621-625 Aspartyl aminopeptidase 621 p-Aspartyl phosphate 539, 540s Assays of enzyme activity 456 Assembly core of virus shell 365 Assembly pathway... 

In many cases the amino acid pathway branches so that two or more amino acids are formed. Aspartate is the precursor of four other amino acids found in proteins Isoleucine, threonine, methionine, and lysine (see fig. 21.2). The first step in this overall pathway entails the conversion of aspartate to /3-aspartyl-phosphate by aspartokinase. One might imagine that all four of the amino acid end products of this pathway would act together to inhibit this enzyme. However, in E. coli a different solution has been found. In this bacterium there are three aspartokinases which appear to be parts of different multienzyme complexes leading to threonine and leucine for aspartokinase I, methionine for aspartokinase II and lysine for aspartokinase III. As might be expected threonine and isoleucine inhibit aspartokinase I,... 

FIGURE 3.4 The common pathway of the aspartate-derived amino acids in Corynebacteria. The mnemonic of the genes involved are shown in parentheses below the enzymes responsible for each step. Dotted lines indicate multiple enzymatic steps, and 16 is L-aspartic acid, 17 is L-aspartyl phosphate, 18 is L-aspartate semialdehyde, 19 is L-lysine, 20 is L-homoserine, 21 is L-isoleucine, 22 is L-threonine, and 23 is L-methionine. 

Since aspartyl phosphates have higher phosphorylating potentials than histidine phosphates, it was postulated that the [32P]polyP-phosphorylated Ca2+-ATPase could transfer the phosphate to a polyP chain as well as back to ADP. The capacity of the [32P]polyP phosphorylated Ca2+-ATPase to carry out these reactions was confirmed (Figure 22A,B), thus demonstrating that the CaATPase has all the enzymatic activities associated with polyphosphate kinases.129... 

Figure 13.3. Phosphoaspartate. Phosphoaspartate (also referred to as P-aspartyl phosphate) is a key intermediate in the reaction cycles of P-type ATPases.

An optimized protocol for the preparation of difluoromethylene phospho-nate (357) an analogue of (3-aspartyl phosphate based on the coupling of protected aspartic acid chloride (358) with difluoromethylphosphonate zinc reagent (359) has been described (Figure 59). ... 

The fluoromethylene and difluoromethylene linkages have also been incorporated into an aspartyl phosphate, providing the first synthetic inhibitors of aspartate semialdehyde dehydrogenase [136] as well as lysophosphatidic acid analogues, which increased the half-lives of analogues in cell culture [137],... 

Cox, R. J., Hadfield, A. T. and Mayo-Martin, M. B. (2001) Difluoromethylene analogues of aspartyl phosphate the first synthetic inhibitors of aspartate semi-aldehyde dehydrogenase. Chem. Commun., 1710-1711. 

The E2 state, formed subsequent to the release of Ca into the lumen and hydrolysis of aspartyl-phosphate, is considered to be the ground state of the enzyme. The cytoplasmic headpiece composed of the A, P, and N domains is compact, as M5 is bent towards Ml to bring the P-domain underneath the TGES loop of the A-domain... 

Aspartyl Phosphate + NADPH + H+ <=> Aspartic Semialdehyde + NADP+ + Pi (catalyzed by Aspartate Semialdehyde Dehydrogenase)... 

Aspartyl-phosphate is an intermediate in the conversion of aspartate to homoserine (see here) in the pathway leading to biosynthesis of threonine, isoleucine, and methionine. 

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