Glutamate 5-phosphate

This enzyme [EC 2.7.2.11], also known as glutamate 5-kinase, catalyzes the reaction of ATP with L-glutamate to produce ADP and L-glutamate 5-phosphate, which is rapidly converted in aqueous solutions to 5-oxoproline and orthophosphate. 

ATP -I- N-acetyl-L-glutamate = ADP -I- N-acetyl-L-glutamate 5-phosphate (<2> random bi-bi mechanism [8] <3> mechanism [9] <6> enzyme has to interact stoichiometrically with acetylglutamate synthase in order to be active [10,12])... 

The direct reduction of glutamate 5-phosphate (Scheme 12.3) with the nicotinamide adenine diphosphate (NADPH)/NADP+-dependent glutamate-5-semialde-hyde dehydrogenase (EC 1.2.1.41) as shown in Scheme 12.5 produces glutamate 5-semialdehyde. The aldehyde spontaneously undergoes cyclization to (5)-3,4-dihydro-2//-pyrrole-2-carboxylate, which is then reduced to L-proline (Pro, P).The reduction is accomplished again with the phosphorylated nicotinamide adenine dinucleotide being oxidized while in the presence of the enzyme pyrroline-5-car-boxylate reductase (EC 1.5.1.2). 

Scheme 12.5. The formation of glutamate 5-semialdehyde from glutamate 5-phosphate and its conversion to L-proline (Pro, P). EC numbers and some graphic materials provided in this scheme have been taken from appropriate links in a URL starting with http // www.chem.qmul.ac.uk/iubmb/enzyme/.

Show the full mechanism for the formation of glutamine by reaction of glutamate 5-phosphate with ammonia, and compare that full mechanism to the abbreviated mechanism shown in Figure 20.12 to see the difference. 

Review Section 16.8, and show the mechanism of the partial reduction of glutamate 5-phosphate with NADH to give glutamate 5-semialdehyde. 

MTX MCC mPEG MA NFX PEO PCS PECs PLA PBLA PLG PPO PEG PCL PBLG PBS PGA Methotrexate Crystalline cellulose Monomethoxypoly(ethylene glycol) Maleic acid Norfloxacin Polyethylene oxide) Photon correlation spectroscopy Poly(electrolyte complexes) Poly(L-lactic acid) Poly( 3-benzyl-L-aspartate) Poly (lactide- co -glycolide) Polypropylene oxide) Polyethylene glycol) Poly(e-caprolactone) Poly(y-benzyl-L-glutamate) Phosphate buffered saline Poly(glycolic acid)... 

The high sensitivity of these systems results from the cyclic conversion of a "shuttle" molecule by two enzymes. In each cycle one diffusible species is formed, which transfers the chemical signal to a transducer. In analogy to metabolic cycles the shuttle molecule flips between its reduced and oxidized or phosphorylated and dephosphorylated state (2). The cyclic reactions are catalyzed by appropriate pairs of enzymes, such as oxidases/dehydrogenases. The shuttle can be any analyte for which such a pair can be constructed, e.g. lactate glutamate, phosphate, ATP or NAD(P)H (3-11). 

The 7 glutamyl phosphate formed m this step is a mixed anhydride of glutamic acid and phosphoric acid It is activated toward nucleophilic acyl substitution and gives glutamine when attacked by ammonia... 

In E. coli GTP cyclohydrolase catalyzes the conversion of GTP (33) into 7,8-dihydroneoptetin triphosphate (34) via a three-step sequence. Hydrolysis of the triphosphate group of (34) is achieved by a nonspecific pyrophosphatase to afford dihydroneopterin (35) (65). The free alcohol (36) is obtained by the removal of residual phosphate by an unknown phosphomonoesterase. The dihydroneoptetin undergoes a retro-aldol reaction with the elimination of a hydroxy acetaldehyde moiety. Addition of a pyrophosphate group affords hydroxymethyl-7,8-dihydroptetin pyrophosphate (37). Dihydropteroate synthase catalyzes the condensation of hydroxymethyl-7,8-dihydropteroate pyrophosphate with PABA to furnish 7,8-dihydropteroate (38). Finally, L-glutamic acid is condensed with 7,8-dihydropteroate in the presence of dihydrofolate synthetase. 

FIGURE 14.22 Glutamate aspartate aminotransferase, an enzyme conforming to a double-displacement bisnbstrate mechanism. Glutamate aspartate aminotransferase is a pyridoxal phosphate-dependent enzyme. The pyridoxal serves as the —NH, acceptor from glntamate to form pyridoxamine. Pyridoxamine is then the amino donor to oxaloacetate to form asparate and regenerate the pyridoxal coenzyme form. (The pyridoxamine enzyme is the E form.)... 

Most amino acids lose their nitrogen atom by a transamination reaction in which the -NH2 group of the amino acid changes places with the keto group of ct-ketoglutarate. The products are a new a-keto acid plus glutamate. The overall process occurs in two parts, is catalyzed by aminotransferase enzymes, and involves participation of the coenzyme pyridoxal phosphate (PLP), a derivative of pyridoxine (vitamin UJ. Different aminotransferases differ in their specificity for amino acids, but the mechanism remains the same. 

The nitrogen source in the medium is the amino add glutamate. There are several cations K Mn2, Cn2, Zn2, Mg2, Co2, Fe2, Ca2 Mo6. Phosphate (POi") is the major anionic component. Fumaric add is a TCA cycle intermediate and may improve metabolic balance through the catabolic pathways and oxidation through the TCA cyde. Peptone may improve growth through the provision of growth factors (amino acids, vitamins, nudeotides). 

Pyridoxamine phosphate serves as a coenzyme of transaminases, e.g., lysyl oxidase (collagen biosynthesis), serine hydroxymethyl transferase (Cl-metabolism), S-aminolevulinate synthase (porphyrin biosynthesis), glycogen phosphoiylase (mobilization of glycogen), aspartate aminotransferase (transamination), alanine aminotransferase (transamination), kynureninase (biosynthesis of niacin), glutamate decarboxylase (biosynthesis of GABA), tyrosine decarboxylase (biosynthesis of tyramine), serine dehydratase ((3-elimination), cystathionine 3-synthase (metabolism of methionine), and cystathionine y-lyase (y-elimination). 

In salt substitutes, the metallic or bitter taste of potassium chloride is often masked by other ingredients, such as the amino acid L-lysine, tricalcium phosphate, citric acid, and glutamic acid. 

In subsequent experiments (66), this locked substrate was used to obtain evidence for the hypothesis (67) that enzyme-bound y-glutamyl phosphate 14 is an intermediate in the enzyme-catalyzed reaction. All attempts to isolate this acyl phosphate 14 have failed (66), presumably because of the marked tendency of this intermediate to cyclize to pyrrolidonecarboxyUc acid, 15, and to hydrolyze to glutamic acid. 

Figure 7-4. Ping-pong mechanism for transamination. E—CHO and E—CHjNHj represent the enzyme-pyridoxal phosphate and enzyme-pyridoxamine complexes, respectively. (Ala, alanine Pyr, pyruvate KG, a-ketoglutarate Glu, glutamate).

The activity of carbamoyl phosphate synthase I is determined by A -acetylglutamate, whose steady-state level is dictated by its rate of synthesis from acetyl-CoA and glutamate and its rate of hydrolysis to acetate and glutamate. These reactions are catalyzed by A -acetylglu-tamate synthase and A -acetylglutamate hydrolase, respectively. Major changes in diet can increase the concentrations of individual urea cycle enzymes 10-fold to 20-fold. Starvation, for example, elevates enzyme levels, presumably to cope with the increased production... 

Figure 30-12. Intermediates in tyrosine catabolism. Carbons are numbered to emphasize their ultimate fate. (a-KG, a-ketoglutarate Glu, glutamate PLP, pyridoxal phosphate.) Circled numerals represent the probable sites of the metabolic defects in type II tyrosinemia neonatal tyrosinemia alkaptonuria and 0 type I tyrosinemia, or tyrosinosis.

C14-0083. Although the ATP-ADP reaction is the principal energy shuttle in metabolic pathways, many other examples of coupled reactions exist. For example, the glutamic acid-glutamine reaction discussed in the text can couple with the acetyl phosphate reaction shown in Example 14-10. Write the balanced equation for the coupled reaction operating in the direction of overall spontaneity and calculate A G ° for the overall process. 

Fig. 8.1 Biosynthesis of peptidoglycan. The large circles represent A -acetylglucosamine orN-acetylmuramic acid to the latter is linked initially a pentapeptide chain comprising L-alanine, D-glutamic acid and meso-diaminopiraelic acid (small circles) terminating in two D-alanine residues (small, darker circles). The lipid molecule is undecaprenyl phosphate. In the initial (cytoplasm) stage where inhibition by the antibiotic D-cycloserine is shown, two molecules of Dalanine (small circles) are converted by an isomerase to the D-forms (small, darker circles), alter which a ligase joins the two D-alanines together to produce a D-alanyl-D-alanine dipeptide.

---