Aspartate oxidation

The second electron shuttle system, called the malate-aspartate shuttle, is shown in Figure 21.34. Oxaloacetate is reduced in the cytosol, acquiring the electrons of NADH (which is oxidized to NAD ). Malate is transported across the inner membrane, where it is reoxidized by malate dehydrogenase, converting NAD to NADH in the matrix. This mitochondrial NADH readily enters the electron transport chain. The oxaloacetate produced in this reaction cannot cross the inner membrane and must be transaminated to form aspartate, which can be transported across the membrane to the cytosolic side. Transamination in the cytosol recycles aspartate back to oxaloacetate. In contrast to the glycerol phosphate shuttle, the malate-aspartate cycle is reversible, and it operates as shown in Figure 21.34 only if the NADH/NAD ratio in the cytosol is higher than the ratio in the matrix. Because this shuttle produces NADH in the matrix, the full 2.5 ATPs per NADH are recovered. 

Because the 2 NADH formed in glycolysis are transported by the glycerol phosphate shuttle in this case, they each yield only 1.5 ATP, as already described. On the other hand, if these 2 NADH take part in the malate-aspartate shuttle, each yields 2.5 ATP, giving a total (in this case) of 32 ATP formed per glucose oxidized. Most of the ATP—26 out of 30 or 28 out of 32—is produced by oxidative phosphorylation only 4 ATP molecules result from direct synthesis during glycolysis and the TCA cycle. 

Oxidation of 2 molecules each of isocitrate, n-ketoglutarate, and malate yields 6 NADH Oxidation of 2 molecules of succinate yields 2 [FADHg] Oxidative phosphorylation (mitochondria) 2 NADH from glycolysis yield 1.5 ATP each if NADH is oxidized by glycerol-phosphate shuttle 2.5 ATP by malate-aspartate shuttle + 3 + 5... 

Fig. 3. Cation-exchange chromatography of protein standards. Column poly(aspartic acid) Vydac (10 pm), 20 x 0.46 cm. Sample 25 pi containing 12.5 pg of ovalbumin and 25 pg each of the other proteins in the weak buffer. Flow rate 1 ml/min. Weak buffer 0.05 mol/1 potassium phosphate, pH 6.0. Strong buffer same +0.6 mol/1 sodium chloride Elution 80-min linear gradient, 0-100% strong buffer. Peaks a = ovalbumin, b = bacitracin, c = myoglobin, d = chymotrypsinogen A, e = cytochrom C (reduced), / = ribonuclease A, g = cytochrome C (oxidised), h = lysozyme. The cytochrome C peaks were identified by oxidation with potassium ferricyanide and reduction with sodium dithionite [47]...

Grb-2 facilitates the transduction of an extracellular stimulus to an intracellular signaling pathway, (b) The adaptor protein PSD-95 associates through one of its three PDZ domains with the N-methyl-D-aspartic acid (NMDA) receptor. Another PDZ domain associates with a PDZ domain from neuronal nitric oxide synthase (nNOS). Through its interaction with PSD-95, nNOS is localized to the NMDA receptor. Stimulation by glutamate induces an influx of calcium, which activates nNOS, resulting in the production of nitric oxide. 

The metabolism of amino acids is complex and is described in standard text books. These are usually converted by aminotransferases to the corresponding 2-oxoacids which are partly oxidized in the matrix of muscle mitochondria and partly exported to the liver. Glutamate and aspartate yield 2-oxoglutarate and oxaloacetate, respectively, which enter the citrate cycle directly, and other 2-... 

In the published synthesis the ozonolysis is performed on the protected product (9) and aldehyde (10) isolated before oxidation, hydrolysis and decarboxylation give aspartic acid. 

Co(lII) perchlorate oxidations of succinic, aspartic, maleic and fumaric acids all obey the rate expression ... 

Metalloenzymes with non-heme di-iron centers in which the two irons are bridged by an oxide (or a hydroxide) and carboxylate ligands (glutamate or aspartate) constitute an important class of enzymes. Two of these enzymes, methane monooxygenase (MMO) and ribonucleotide reductase (RNR) have very similar di-iron active sites, located in the subunits MMOH and R2 respectively. Despite their structural similarity, these metal centers catalyze very different chemical reactions. We have studied the enzymatic mechanisms of these enzymes to understand what determines their catalytic activity [24, 25, 39-41]. 

Langsetmo K, Fuchs JA, Woodward C (1991) The conserved, buried aspartic acid in oxidized Escherichia coli thioredoxin has a pKa of 7.5. its titration produces a related shift in global stability Biochemistry 30 7603-7609. 

Fedele, E., Varnier, G., Ansaldo, M.A., Raiteri, M. Nicotine administration stimulates the in vivo N-methyl-D-aspartate receptor/nitric oxide/cyclic GMP pathway in rat hippocampus through glutamate release. Br. J. Pharmacol. 125 1042, 1998. 

A number of P-chirogenic diaminophosphine oxides (DIAPHOXs) 275 derived from aspartic acid were prepared via hydrolysis of triaminophosphine intermediate 274, generated in a fully diastereoselective reaction of triamines 273 with phosphorus trichloride (Scheme 65) [102, 103],... 

H. Yokoyama, N. Mori, N. Kasai, T. Matsue, I. Uchida, N. Kobayashi, N. Tsuchihashi, T. Yoshimura, M. Hiramatsu, and S.I. Niwa, Direct and continuous monitoring of intrahippocampal nitric oxide (NO) by an NO sensor in freely moving rat after N-methyl-D-aspartic acid injection. Denki Kagaku 63, 1167-1170 (1995). 

Figures 11(a) and 11(b) [112] show the variation of Ni-Ge-P deposition rate and Ge content as a function of aspartic acid and Ge(IV) concentration, respectively. A relatively low P content, ca. 1-2 at%, was observed in the case of films exhibiting a high concentration of Ge (> 18 at%). Like other members of its class, which includes molybdate and tungstate, Ge(IY) behaves a soft base according to the hard and soft acids and bases theory (HSAB) originated by Pearson [113, 114], capable of strong adsorption, or displaying inhibitor-like behavior, on soft acid metal surfaces. In weakly acidic solution, uncomplexed Ge(IV) most probably exists as the hydrated oxide, or Ge(OH)4, which, due to acid-base reactions, may be more accurately represented as [Gc(OH)4 nO ] ".

The other shuttle is the malate-aspartate shuttle. The advantage of this shuttle is that it gives you 3 ATPs for the oxidation of each cytoplasmic NADH. In red muscle, heart, and brain tissues the malate-aspartate shuttle is the major pathway for shuttling electrons into mitochondria. In white muscle, the a-glycerol phosphate shuttle predominates (Fig. 14-2). 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

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