Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0344329 (collapse)
 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The chemical and kinetic mechanisms of purified aspartate-beta-semialdehyde dehydrogenase from Escherichia coli have been determined. The kinetic mechanism of the enzyme, determined from initial velocity, product and dead end inhibition studies, is a random preferred order sequential mechanism. For the reaction examined in the phosphorylating direction L-aspartate-beta-semialdehyde binds preferentially to the E-NADP-Pi complex, and there is random release of the products L-beta-aspartyl phosphate and NADPH. Substrate inhibition is displayed by both Pi and NADP. Inhibition patterns versus the other substrates suggest that Pi inhibits by binding to the phosphate subsite in the NADP binding site, and the substrate inhibition by NADP results from the formation of a dead end E-beta-aspartyl phosphate-NADP complex. The chemical mechanism of the enzyme has been examined by pH profile and chemical modification studies. The proposed mechanism involves the attack of an active site cysteine sulfhydryl on the carbonyl carbon of aspartate-beta-semialdehyde, with general acid assistance by an enzyme lysine amino group. The resulting thiohemiacetal is oxidized by NADP to a thioester, with subsequent attack by the dianion of enzyme bound phosphate. The collapse of the resulting tetrahedral intermediate leads to the acyl-phosphate product and liberation of the active site cysteine.
 ...
PMID:Chemical and kinetic mechanisms of aspartate-beta-semialdehyde dehydrogenase from Escherichia coli. 167 60

Isolated rat hepatocytes were incubated with ATP to induce high intracellular free Ca2+ concentrations as determined with the Quin-2 method. Immediately after addition of ATP, the intracellular concentration of Ca2+ rose from 200 nM to more than 2.5 microM. It stayed at this value during the first 1/2 h; the rise was absolutely dependent on extracellular Ca2+. After the first 1/2 h the Ca2+ concentration decreased to 1-2 microM (5-10 times the control value). These high intracellular free Ca2+ concentrations did not lead to an immediate loss of cell viability. Only after 2 h of incubation a substantial number of cells lost viability. This was preceded by a decrease in cellular NADH (greater than 40%) and accompanied by a sharp increase in the intracellular Ca2+ concentration. Under these conditions the NADPH concentration was not affected. Cellular GSH was decreased to 30% of the initial value, but no lipid peroxidation or protein-thiol depletion was observed. Intracellular ATP, ADP and AMP were increased in the presence of extracellular ATP. Ca2+-dependent proteases seemed not to be involved in cell death. These observations are consistent with a collapse of mitochondrial functions as a final trigger of cell death.
 ...
PMID:Prolonged high intracellular free calcium concentrations induced by ATP are not immediately cytotoxic in isolated rat hepatocytes. Changes in biochemical parameters implicated in cell toxicity. 259 7

The subcellular distribution of the Na+/H+ antiporter in renal proximal tubule cells was studied with differential and density gradient centrifugation. Enzyme markers for basolateral membranes [Na+/K+)-ATPase), brush border membranes (maltase), and a variety of intracellular organelles (NADPH cytochrome c reductase, thiamine pyrophosphatase, acid phosphatase, and succinate cytochrome c reductase) were simultaneously assayed in sucrose density gradients. Basolateral membranes (median rho = 1.150) were well separated from brush border membranes (median rho = 1.165) by this technique. Markers for other cellular organelles had intermediate or bimodal distributions. To determine the cellular location of the Na+/H+ antiporter, Na+-dependent collapse of preformed pH gradients was assayed in the sucrose density gradient fractions using acridine orange. Na+/H+ antiporter activity paralleled the distribution of the brush border membrane fractions; activity in the peak basolateral membrane fraction was less than 5% of that in the peak brush border fraction. To determine whether antiporter activity was potentially detectable in all cell fractions, nigericin was added to each fraction and K+/H+ exchange was assayed with acridine orange. Activity was present in all sucrose density gradient fractions. In addition, there was no alteration in Na+/H+ exchange activity measured in brush border membranes after mixing with cell sol or basolateral membranes, showing that neither inhibitors nor activators of the Na+/H+ antiporter were present in any of the cell fractions. These controls confirmed the finding that Na+/H+ antiporter activity was absent from basolateral membranes. The presence of the Na+/H+ antiporter in brush border membranes and its absence from basolateral membranes is consistent with its playing an important role in the vectorial transport of H+ from blood to tubular lumen in the renal proximal tubule.
 ...
PMID:Asymmetric distribution of the Na+/H+ antiporter in the renal proximal tubule epithelial cell. 631 99

Homogeneous bovine heart mitochondrial transhydrogenase was reconstituted into K+-loaded phosphatidylcholine liposomes. Transhydrogenase-catalyzed reduction of 3-acetylpyridine adenine dinucleotide by NADPH was stimulated severalfold when valinomycin was added to collapse the developing membrane potential. A rapid and extensive quenching of the fluorescence of the pH probe, 9-aminoacridine, under these conditions indicates that transhydrogenation is coupled to the acidification of the vesicle interior. A corresponding uptake of protons from the medium is demonstrated by electrode measurements that indicate 1 or less proton is translocated for each hydride ion equivalent transferred between the substrates.
 ...
PMID:A direct demonstration of proton translocation coupled to transhydrogenation in reconstituted vesicles. 735 61

Exogenous NADPH oxidation by purified mitochondria from both potato tuber and Arum maculatum spadix was completely and irreversibly inhibited by sub-micromolar diphenyleneiodonium (DPI), while exogenous NADH oxidation was inhibited to only a small degree. Addition of DPI caused the collapse of the membrane potential generated by NADPH oxidation, while the potential generated by NADH was unaffected. We conclude that there are two distinct enzymes on the outer surface of the inner membrane of plant mitochondria, one specific for NADH, the other relatively specific for NADPH, with both enzymes linked to the electron transport chain.
 ...
PMID:Direct evidence for the presence of two external NAD(P)H dehydrogenases coupled to the electron transport chain in plant mitochondria. 758 89

In order to investigate the relationship between nitric oxide-mediated regulation of mitochondrial function and excitotoxicity, the role of mitochondrial ATP synthesis and intracellular redox status on the mode of neuronal cell death was studied. Brief (5 min) glutamate (100 microM) receptor stimulation in primary cortical neurons collapsed the mitochondrial membrane potential (psi(m)) and transiently (30 min) inhibited mitochondrial ATP synthesis, causing early (1 h) necrosis or delayed (24 h) apoptosis. The transient inhibition of ATP synthesis was paralleled to a loss of NADH, which was fully recovered shortly after the insult. In contrast, NADPH and the GSH/GSSG ratio were maintained, but progressively decreased thereafter. Twenty-four hours after glutamate treatment, ATP was depleted, a phenomenon associated with a persistent inhibition of mitochondrial succinate-cytochrome c reductase activity and delayed necrosis. Blockade of either nitric oxide synthase (NOS) activity or the mitochondrial permeability transition (MPT) pore prevented psi(m) collapse, the transient inhibition of mitochondrial ATP synthesis, early necrosis and delayed apoptosis. However, blockade of NOS activity, but not the MPT pore, prevented the inhibition of succinate-cytochrome c reductase activity and delayed ATP depletion and necrosis. From these results, we suggest that glutamate receptor-mediated NOS activation would trigger MPT pore opening and transient inhibition of ATP synthesis leading to apoptosis in a neuronal subpopulation, whereas other groups of neurons would undergo oxidative stress and persistent inhibition of ATP synthesis leading to necrosis.
 ...
PMID:A transient inhibition of mitochondrial ATP synthesis by nitric oxide synthase activation triggered apoptosis in primary cortical neurons. 1129 30

The redox state of mitochondrial pyridine nucleotides is known to be important for structural integrity of mitochondria. In this work, we observed a biphasic oxidation of endogenous NAD(P)H in rat liver mitochondria induced by tert-butylhydroperoxide. Nearly 85% of mitochondrial NAD(P)H was rapidly oxidized during the first phase. The second phase of NAD(P)H oxidation was retarded for several minutes, appearing after the inner membrane potential collapse and mitochondria swelling. It was characterized by disturbance of ATP synthesis and dramatic permeabilization of the inner membrane to pyridine nucleotides. The second phase was completely prevented by 0.5 microM cyclosporin A or 0.2 mM EGTA or was significantly delayed by 25 microM butylhydroxytoluene or trifluoperazine. The obtained data suggest that the second phase resulted from oxidation of the remaining NADH via the outer membrane electron transport system of permeabilized mitochondria, leading to further oxidation of the remaining NADPH in a transhydrogenase reaction.
 ...
PMID:Biphasic oxidation of mitochondrial NAD(P)H. 1182 79

In order to investigate the potential neuroprotective role played by glucose metabolism during brain oxygen deprivation, the susceptibility of cultured neurones and astrocytes to 1 h of oxygen deprivation (hypoxia) or oxygen and glucose deprivation (OGD) was examined. OGD, but not hypoxia, promotes dihydrorhodamine 123 and glutathione oxidation in neurones but not in astrocytes reflecting free radical generation in the former cells. A specific loss of mitochondrial complex-I activity, mitochondrial membrane potential collapse, ATP depletion and necrosis occurred in the OGD neurones, but not in the OGD astrocytes. Furthermore, superoxide anion but not nitric oxide formation was responsible for these effects. OGD decreased neuronal but not astrocytic NADPH concentrations; this was not observed in hypoxia and was independent of superoxide or nitric oxide formation. These results suggest that glucose metabolism would supply NADPH, through the pentose-phosphate pathway, aimed at preventing oxidative stress, mitochondrial damage and neurotoxicity during oxygen deprivation to neural cells.
 ...
PMID:Oxygen and glucose deprivation induces mitochondrial dysfunction and oxidative stress in neurones but not in astrocytes in primary culture. 1206 68

The NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase (2-KPCC) is the terminal enzyme in a metabolic pathway that results in the conversion of propylene to the central metabolite acetoacetate in Xanthobacter autotrophicus Py2. This enzyme is an FAD-containing enzyme that is a member of the NADPH:disulfide oxidoreductase (DSOR) family of enzymes that include glutathione reductase, dihydrolipoamide dehydrogenase, trypanothione reductase, thioredoxin reductase, and mercuric reductase. In contrast to the prototypical reactions catalyzed by members of the DSOR family, the NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase catalyzes the reductive cleavage of the thioether linkage of 2-ketopropyl-coenzyme M, and the subsequent carboxylation of the ketopropyl cleavage product, yielding the products acetoacetate and free coenzyme M. The structure of 2-KPCC reveals a unique active site in comparison to those of other members of the DSOR family of enzymes and demonstrates how the enzyme architecture has been adapted for the more sophisticated biochemical reaction. In addition, comparison of the structures in the native state and in the presence of bound substrate indicates the binding of the substrate 2-ketopropyl-coenzyme M induces a conformational change resulting in the collapse of the substrate access channel. The encapsulation of the substrate in this manner is reminiscent of the conformational changes observed in the well-characterized CO2-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxidase (Rubisco).
 ...
PMID:Structural basis for CO2 fixation by a novel member of the disulfide oxidoreductase family of enzymes, 2-ketopropyl-coenzyme M oxidoreductase/carboxylase. 1239 15

Previously we showed that 10 muM glyoxal compromised hepatocyte resistance to hydrogen peroxide (H(2)O(2)) by increasing glutathione (GSH) and NADPH oxidation and decreasing mitochondrial membrane potential (MMP) before cytotoxicity ensued. Since transition metal-catalyzed oxidation of ascorbate (Asc) has been shown to result in the generation of both glyoxal and H(2)O(2), we hypothesized that glyoxal formation during this process compromises hepatocyte resistance to H(2)O(2). We used isolated rat hepatocytes and incubated them with Asc/copper and measured cytotoxicity, glyoxal levels, H(2)O(2), GSH levels, and MMP. To investigate the role of Asc/copper on glyoxal-BSA adducts, we measured the appearance of advanced glycation end-products (AGE) in the presence and absence of catalase or aminoguanidine (AG). Asc/copper increased glyoxal and H(2)O(2) formation. Hepatocyte GSH levels were decreased and cytotoxicity ensued after a collapse of the hepatocyte MMP. Glyoxal traps protected hepatocytes against Asc/copper-induced cytotoxicity. In cell-free studies with BSA, incubation with Asc and copper resulted in glyoxal-hydroimidazolone formation, which was decreased by both AG and catalase. To the best of our knowledge, this is the first study that illustrates the importance of glyoxal production by transition metal-catalyzed Asc autoxidation. Understanding this mechanism of toxicity could lead to the development of novel copper chelating drug therapies to treat diabetic complications.
 ...
PMID:Copper-catalyzed ascorbate oxidation results in glyoxal/AGE formation and cytotoxicity. 1739 Mar 97


1 2 Next >>