An integrated microfluidic device for influenza and other genetic analyses

An integrated microfluidic device capable of performing a variety of genetic assays has been developed as a step towards building systems for widespread dissemination. The device integrates fluidic and thermal components such as heaters, temperature sensors, and addressable valves to control two nanoliter reactors in series followed by an electrophoretic separation. This combination of components is suitable for a variety of genetic analyses. As an example, we have successfully identified sequence-specific hemagglutinin A subtype for the A/LA/1/87 strain of influenza virus. The device uses a compact design and mass production technologies, making it an attractive platform for a variety of widely disseminated applications.

Disruption of the structure of the Golgi apparatus and the function of the secretory pathway by mutants G93A and G85R of Cu, Zn superoxide dismutase (SOD1) of familial amyotrophic lateral sclerosis

The Golgi apparatus of motor neurons (GA) is fragmented in sporadic amyotrophic lateral sclerosis (ALS), in familial ALS with SOD1 mutations, and in mice that express SOD1G93A of familial ALS, in which it was detected months before paralysis. In paralyzed transgenic mice expressing SOD1G93A or SOD1G85R, mutant proteins aggregated not only in the cytoplasm of motor neurons, but also in astrocytes and oligodendrocytes. Furthermore, aggregation of the G85R protein damaged astrocytes and was associated with rapidly progressing disease. In order to gain insight into the functional state of the fragmented GA, we examined the effects of S0D1 mutants G93A and G85R in Chinese Hamster Ovary Cells (CHO). In contrast to cells expressing the wt and G93A, the G85R expressers had no SOD1 activity. However, cells expressing both mutants, and to a lesser degree the wt, showed decreased survival, fragmentation of the GA, and dysfunction of the secretory pathway, which was assessed by measuring the amount of cell surface co-expressed CD4, a glycoprotein processed through the GA. The G93A and wt proteins were partially recovered in detergent insoluble fractions; while the recovery of G85R was minimal. Both mutants showed equal reductions of cell survival and function of the secretory pathway, in comparison to the wt and cells expressing mutant alsin, a protein found in rare cases of fALS. These results are consistent with the conclusion that the two SOD1 mutants, by an unknown mechanism, promote the dispersion of the GA and the dysfunction of the secretory pathway. This and other in vitro models of mutant SOD1 toxicity may prove useful in the elucidation of pathogenetic mechanisms.

Protein glycation: creation of catalytic sites for free radical generation

In a glycation reaction, alpha-dicarbonyl compounds such as deoxyglucosone, methylglyoxal, and glyoxal are more reactive than the parent sugars with respect to their ability to react with amino groups of proteins to form inter- and intramolecular cross-links of proteins, stable end products called advanced Maillard products or advanced end products (AGEs). The AGEs, which are irreversibly formed, accumulate with aging, atherosclerosis, and diabetes mellitus, and are especially associated with long-lived proteins such as collagens, lens crystallins, and nerve proteins. It was suggested that the formation of AGEs not only modifies protein properites but also induces biological damage in vivo. In this report, we summerize results obtained from our studies for (1) identifying the structure of the cross-linked radical species formed in the model system-the reaction between alpha-dicarbonyl methylglyoxal with amino acids, and (2) the reactivity of the radical center of the protein created by the similar reaction. These results indicate that glycation of protein generates active centers for catalyzing one-electron oxidation-reduction reactions. This active center, which exhibits enzyme-like character, is suggested to be the cross-linked Schiff-based radical cation of the protein. It mimics the characteristics of the metal-catalyzed oxidation system. These results together indicate that glycated proteins accumulated in vivo provide stable active sites for catalyzing the formation of free redicals.

A co-operative study: clinical characteristics of 334 Korean patients with moyamoya disease treated at neurosurgical institutes (1976-1994). The Korean Society for Cerebrovascular Disease

A co-operative study was conducted to determine the clinical characteristics of patients with moyamoya disease who were diagnosed and treated at neurosurgical institutes in Korea before 1995. Twenty-six hospitals contributed 505 cases and among them, the clinical characteristics of 334 patients with definite moyamoya disease were evaluated. The number of patients began to increase from the late 1980s, and after that approximately 20 patients were treated each year. There were two age peaks: from six to 15 and from 31 to 40 years of age. Haemorrhagic manifestations occurred in approximately 43% of the patients. The major clinical manifestations were haemorrhage in adults (62.4%) and ischaemia in children (61.2%). Overall 54.5% of the patients experienced decreased consciousness levels, mainly due to intracranial haemorrhage or cerebral infarction. In the patients with ischemic manifestations, the adult patients were more likely to have cerebral infarction than the pediatric patients (80% vs. 39%) and the pediatric patients were more likely to have TIA (61% vs. 25%). Thirty eight percent of the patients underwent bypass surgery and 53% of these procedures were performed bilaterally. Treatment policies, including indications for bypass surgery and commonly used drugs, were somewhat different according to the institution. Overall favorable outcome was 73%, and the most significant factor affecting poor outcome was haemorrhagic manifestation. This article describes the characteristics of 334 patients with moyamoya disease, who were diagnosed and treated at neurosurgical institutes in Korea before 1995.

Enzyme-like activity of glycated cross-linked proteins in free radical generation

The structure and property of cross-linked amino acids and proteins produced by a three- carbon alpha-dicarbonyl methylglyoxal in glycation reaction were investigated. Our results showed that these reactions generated yellow fluorescent products and several free radical species. From the reaction with alanine, three types of free radicals were identified by EPR spectroscopy: 1) the cross-linked radical cation, methylglyoxal diaklylimine cation radical; 2) the methylglyoxal radical anion as the counterion; 3) the superoxide radical anion produced only in the presence of oxygen. Glycation of bovine serum albumin by methylglyoxal also generated the protein-bound, cross-linked free radical, probably the cation radical of the cross-linked Schiff base as observed with alanine. The glycated protein reduced ferricytochrome c to ferrocytochrome c in the absence of oxygen or added metal ions. This reduction of cytochrome c was accompanied by a large increase in the amplitude of the electron paramagnetic resonance signal originated from the protein-bound free radical. In addition, the glycated protein catalyzed the oxidation of ascorbate in the presence of oxygen while the protein-free radical signal disappeared. These results indicate that glycation of protein generates active centers for catalyzing one-electron oxidation-reduction reactions. This active center, which exhibits enzyme-like character, was suggested to be the cross-linked Schiff base/the cross-linked Schiff base radical cation of the protein. It mimics the characteristics of metal-catalyzed oxidation system. These results together indicate that glycated proteins accumulated in vivo provide stable active-sites for catalyzing the formation of free radicals.

Transcriptional activation of the human manganese superoxide dismutase gene mediated by tetradecanoylphorbol acetate

Transcriptional activation of human manganese superoxide dismutase (MnSOD) mRNA induced by a phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), was examined to identify the responsive transcriptional regulator. The effect of various deletions and mutations within the 5'-flanking region of the human MnSOD gene promoter was evaluated using the luciferase reporter system in A549 human lung carcinoma cells. Deletion of a region between -1292 and -1202 nucleotides upstream of the transcription start site abolished TPA-responsive induction, whereas deletion of the putative binding sequence for NF-kappaB or AP-1 did not. The region between -1292 and -1202 contains a cAMP-responsive element-like sequence, TGACGTCT, which we identified as the manganese superoxide dismutase TPA-responsive element, MSTRE. Site-specific mutation of the MSTRE abolished the TPA-responsive induction, validating the critical role of this sequence. We detected specific MSTRE activity from nuclear extracts and demonstrated by antibody supershift assay that this activity is closely related to CREB-1/ATF-1. TPA treatment rapidly induced phosphorylation of the CREB-1/ATF-1-like factor via the protein kinase C pathway. These results led us to conclude that the human MnSOD gene having the promoter construct used in this study is induced by TPA via activation of a CREB-1/ATF-1-like factor and not via either NF-kappaB or AP-1. In addition, we found that this induction was blocked by inhibitors of flavoproteins and NADPH oxidases, indicating involvement of enhanced generation of superoxide radical anion as an upstream signal.

Roles of superoxide radical anion in signal transduction mediated by reversible regulation of protein-tyrosine phosphatase 1B

Growth factors induce intracellular production of reactive oxygen species in non-phagocytic cells and elevation of their phosphorylated protein tyrosine level. The latter can be achieved by activating protein-tyrosine kinases and/or inactivating protein-tyrosine phosphatases (PTPs). A highly abundant PTP, PTP-1B, is known to be inactivated by oxidation of its catalytic site Cys-215. We show that O-(2) is kinetically more efficient and chemically more specific oxidant than H(2)O(2) for inactivating PTP-1B. The second-order rate constant for the O-(2)- and H(2)O(2)-mediated inactivation is 334 +/- 45 M(-1) s(-1) and 42.8 +/- 3.8 M(-1) s(-1), respectively. PTP-1B oxidized by H(2)O(2) exhibits significantly more oxidized methionine residues and shows a lower degree of reversibility. The initial oxidative product, the Cys-215 sulfenic derivative, can easily be oxidized further to its irreversible sulfinic and sulfonic derivatives. This step is prevented by glutathionylation of the sulfenic derivative to form a S-glutathionylated PTP-1B, which can be reactivated by dithiothreitol or thioltransferase. Thus, a signal transduction mechanism mediated by the O-(2) and the participation of glutathione is proposed for the regulation of PTP-1B. This mechanism is supported by the in vivo demonstration that glutathionylated PTP-1B at Cys-215 is formed in A431 cells when they were treated with epidermal growth factor.

Enhanced free radical generation of FALS-associated Cu,Zn-SOD mutants

Familial amyotrophic lateral sclerosis (FALS) is an inherited disorder of motor neurons, which is associated with missense mutations in the Cu,Zn-superoxide dismutase (Cu,Zn-SOD) gene. Mice from the G93A transgenic line were reported to develop a syndrome of FALS. The fact that the symptoms occurred against a background of normal mouse Cu,Zn-SOD activity suggests that dominant, gain-of-function mutations in SOD play a role in the pathogenesis of FALS. We investigated the nature of this gain-of-function of FALS mutants. We have previously reported that Cu,Zn-SOD has the free radical-generating function in addition to normal dismutation activity. These two enzymic activities were compared by using mutants (G93A and A4V) and the wild-type Cu,Zn-SOD prepared by recombinant method. Our results showed that the wild-type, G93A, and A4V enzymes have identical dismutation activity. However, the free radical-generating function of the G93A and A4V mutants, as measured by the spin trapping and EPR method, is enhanced relative to that of the wild-type enzyme (wild type < G93A < A4V), particularly at lower H(2)O(2) concentrations. This is due to the decrease in the K(m) value for H(2)O(2), wild-type > G93A > A4V. The catalytic activity to generate free radicals is correlated to the clinical severity of the disorder induced by these mutant enzymes. Furthermore, we found that intact FALS mutants failed to enhance tyrosine nitration. Together our results indicate that the amyotrophic lateral sclerosis symptoms are not caused by the reduction of Cu,Zn-SOD dismutation activity with the mutant enzymes; rather, it is induced in part by enhancement of the free radical-generating function.

Regulation of PTP1B via glutathionylation of the active site cysteine 215

The reversible regulation of protein tyrosine phosphatase is an important mechanism in processing signal transduction and regulating cell cycle. Recent reports have shown that the active site cysteine residue, Cys215, can be reversibly oxidized to a cysteine sulfenic derivative (Denu and Tanner, 1998; Lee et al., 1998). We propose an additional modification that has implications for the in vivo regulation of protein tyrosine phosphatase 1B (PTP1B, EC 3.1.3.48): the glutathionylation of Cys215 to a mixed protein disulfide. Treatment of PTP1B with diamide and reduced glutathione or with only glutathione disulfide (GSSG) results in a modification detected by mass spectrometry in which the cysteine residues are oxidized to mixed disulfides with glutathione. The activity is recovered by the addition of dithiothreitol, presumably by reducing the cysteine disulfides. In addition, inactivated PTP1B is reactivated enzymatically by the glutathione-specific dethiolase enzyme thioltransferase (glutaredoxin), indicating that the inactivated form of the phosphatase is a glutathionyl mixed disulfide. The cysteine sulfenic derivative can easily oxidize to its irreversible sulfinic and sulfonic forms and hinder the regulatory efficiency if it is not converted to a more stable and reversible end product such as a glutathionyl derivative. Glutathionylation of the cysteine sulfenic derivative will prevent the enzyme from further oxidation to its irreversible forms, and constitutes an efficient regulatory mechanism.

Oxidation-reduction properties of methylglyoxal-modified protein in relation to free radical generation

Oxidation-reduction properties of methylglyoxal-modified protein in relation to free radical generation were investigated. Glycation of bovine serum albumin by methylglyoxal generated the protein-bound free radical, probably the cation radical of the cross-linked Schiff base, as observed in the reaction of methylglyoxal with L-alanine (Yim, H.-S., Kang, S.-O., Hah, Y. C., Chock, P. B., and Yim, M. B. (1995) J. Biol. Chem. 270, 28228-28233) or with Nalpha-acetyl-L-lysine. The glycated bovine serum albumin showed increased electrophoretic mobility suggesting that the basic residues, such as lysine, were modified by methylglyoxal. The glycated protein reduced ferricytochrome c to ferrocytochrome c in the absence of oxygen or added metal ions. This reduction of cytochrome c was accompanied by a large increase in the amplitude of the electron paramagnetic resonance signal originated from the protein-bound free radical. In addition, the glycated protein catalyzed the oxidation of ascorbate in the presence of oxygen, whereas the protein free radical signal disappeared. These results indicate that glycation of protein generates active centers for catalyzing one-electron oxidation-reduction reactions. This active center, which exhibits enzyme-like characteristic, was suggested to be the cross-linked Schiff base/the cross-linked Schiff base radical cation of the protein. It mimics the characteristics of the metal-catalyzed oxidation system. The glycated bovine serum albumin cross-linked further to the cytochrome c in the absence of methylglyoxal. The cross-linked cytochrome c maintains its oxidation-reduction properties. These results together indicate that glycated proteins accumulated in vivo provide stable active sites for catalyzing the formation of free radicals.

Reactivity of the flavin semiquinone of nitric oxide synthase in the oxygenation of arginine to NG-hydroxyarginine, the first step of nitric oxide synthesis

Nitric oxide synthase (NOS) is a heme protein that catalyzes the oxygenation of L-arginine in the presence of NADPH to form nitric oxide, L-citrulline and NADP+, and proceeds via two partial reactions: 1) L-Arginine --> NG-hydroxy-L-arginine 2) NG-Hydroxy-L-arginine --> L-citrulline + nitric oxide Calmodulin, FAD, FMN and tetrahydrobiopterin are required for both reactions. Reactions 1 and 2 require the input of 2 and 1 electron equivalents, respectively. Under normal multiple turnover conditions, these electrons are ultimately derived from NADPH. We previously reported that NOS contains an endogenous reductant that, in the absence of NADPH, can support the single-turnover oxygenation of L-arginine to NG-hydroxy-L-arginine and a relatively small amount of L-citrulline [Campos, K. L., Giovanelli, J., and Kaufman, S. (1995) J. Biol. Chem. 270, 1721-1728]. This reductant has now been identified as the stable flavin semiquinone free radical (FSQ). Its oxidation appears to be coupled to the formation of NG-hydroxy-L-arginine and L-citrulline. The rate of FSQ oxidation is two orders of magnitude slower than the flux of electrons from NADPH through NOS during normal turnover of the enzyme, indicating that FSQ is not the proximal electron donor for heme under these conditions.

A familial amyotrophic lateral sclerosis-associated A4V Cu, Zn-superoxide dismutase mutant has a lower Km for hydrogen peroxide. Correlation between clinical severity and the Km value

Point mutations of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) have been linked to familial amyotrophic lateral sclerosis (FALS). We reported that Cu,Zn-SOD can catalyze free radical generation and a FALS mutant, G93A, exhibits an enhanced free radical-generating activity, while its dismutation activity is identical to that of the wild-type enzyme (Yim, M. B., Kang, J.-H., Yim, H.-S., Kwak, H.-S., Chock, P. B., and Stadtman, E. R. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 5709-5714). The A4V mutation is both the most commonly detected of FALS-associated SOD1 mutations and among the most clinically severe (Rosen, D. R., Bowling, A. C., Patterson, D., Usdin, T. B., Sapp, P., Mezey, E., McKenna-Yasek, D., O'Regan, J. P., Rahmani, Z., Ferrante, R. J., Brownstein, M. J., Kowall, N. W., Beal, M. F., Horvitz, H. R., and Brown, R. H., Jr. (1994) Hum. Mol. Genet. 3, 981-987). We cloned the cDNA for the FALS A4V mutant, overexpressed the protein in Sf9 insect cells, purified the protein, and studied its enzymic activities. Our results show that the mutant and wild-type enzymes contain one copper ion per subunit and have identical dismutation activities. However, the free radical-generating activity of the mutant, as measured by the spin trapping method at low H2O2 concentration, is enhanced relative to that of the wild-type and G93A enzyme (wild-type < G93A < A4V). This is due to the decrease in the Km value for H2O2, wild-type > G93A > A4V, while the kcat is identical for these enzymes. Thus, the FALS symptoms are not associated with the reduction in the dismutation activity of the mutant enzyme. The fact that the A4V mutant has the lowest Km for H2O2 is correlated to the clinical severity observed with the A4V patients, if FALS is associated with a differential gain of the free radical-generating function of the Cu,Zn-SOD mutant.

A gain-of-function of an amyotrophic lateral sclerosis-associated Cu,Zn-superoxide dismutase mutant: An enhancement of free radical formation due to a decrease in Km for hydrogen peroxide

Cu,Zn-superoxide dismutase (SOD) is known to be a locus of mutation in familial amyotrophic lateral sclerosis (FALS). Transgenic mice that express a mutant Cu,Zn-SOD, Gly-93--> Ala (G93A), have been shown to develop amyotrophic lateral sclerosis (ALS) symptoms. We cloned the FALS mutant, G93A, and wild-type cDNA of human Cu,Zn-SOD, overexpressed them in Sf9 insect cells, purified the proteins, and studied their enzymic activities for catalyzing the dismutation of superoxide anions and the generation of free radicals with H2O2 as substrate. Our results showed that both enzymes contain one copper ion per subunit and have identical dismutation activity. However, the free radical-generating function of the G93A mutant, as measured by the spin trapping method, is enhanced relative to that of the wild-type enzyme, particularly at lower H2O2 concentrations. This is due to a small, but reproducible, decrease in the value of Km for H2O2 for the G93A mutant, while the kcat is identical for both enzymes. Thus, the ALS symptoms observed in G93A transgenic mice are not caused by the reduction of Cu,Zn-SOD activity with the mutant enzyme; rather, it is induced by a gain-of-function, an enhancement of the free radical-generating function. This is consistent with the x-ray crystallographic studies showing the active channel of the FALS mutant is slightly larger than that of the wild-type enzyme; thus, it is more accessible to H2O2. This gain-of-function, in part, may provide an explanation for the association between ALS and Cu,Zn-SOD mutants.

Peroxynitrite disables the tyrosine phosphorylation regulatory mechanism: Lymphocyte-specific tyrosine kinase fails to phosphorylate nitrated cdc2(6-20)NH2 peptide

To determine if nitration of tyrosine residues by peroxynitrite (PN), which can be generated endogenously, can disrupt the phosphorylation of tyrosine residues in proteins involved in cell signaling networks, we studied the effect of PN-promoted nitration of tyrosine residues in a pentadecameric peptide, cdc2(6-20)NH2, on the ability of the peptide to be phosphorylated. cdc2(6-20)NH2 corresponds to the tyrosine phosphorylation site of p34cdc2 kinase, which is phosphorylated by lck kinase (lymphocyte-specific tyrosine kinase, p56lck). PN nitrates both Tyr-15 and Tyr-19 of the peptide in phosphate buffer (pH 7.5) at 37 degrees C. Nitration of Tyr-15. which is the phosphorylated amino acid residue, inhibits completely the phosphorylation of the peptide. The nitration reaction is enhanced by either Fe(III)EDTA or Cu(II)-Zn(II)-superoxide dismutase (Cu,Zn-SOD). The kinetic data are consistent with the view that reactions of Fe(111)EDTA or Cu,Zn-SOD with the cis form of PN yield complexes in which PN decomposes more slowly to form N02+, the nitrating agent. Thus, the nitration efficiency of PN is enhanced. These results are discussed from the point of view that PN-promoted nitration will result in permanent impairment of cyclic cascades that control signal transduction processes and regulate cell cycles.

Peroxynitrite-mediated nitration of tyrosine residues in Escherichia coli glutamine synthetase mimics adenylylation: relevance to signal transduction

Treatment of Escherichia coli glutamine synthetase (GS) with peroxynitrite leads to nitration of some tyrosine residues and conversion of some methionine residues to methionine sulfoxide (MSOX) residues. Nitration, but not MSOX formation, is stimulated by Fe-EDTA. In the absence of Fe-EDTA, nitration of only one tyrosine residue per subunit of unadenylylated GS leads to changes in divalent cation requirement, pH-activity profile, affinity for ADP, and susceptibility to feedback inhibition by end products (tryptophan, AMP, CTP), whereas nitration of one tyrosine residue per subunit in the adenylylated GS leads to complete loss of catalytic activity. In the presence of Fe-EDTA, nitration is a more random process: nitration of five to six tyrosine residues per subunit is needed to convert unadenylylated GS to the adenylylated configuration. These results and the fact that nitration of tyrosine residues is an irreversible process serve notice that the regulatory function of proteins that undergo phosphorylation or adenylylation in signal transduction cascades might be seriously compromised by peroxynitrite-promoted nitration.

Free radicals generated during the glycation reaction of amino acids by methylglyoxal. A model study of protein-cross-linked free radicals

The formation of alpha-dicarbonyl compounds seems to be an important step for cross-linking proteins in the glycation or Maillard reaction. To elucidate the mechanism for the cross-linking reaction, we studied the reaction between a three-carbon alpha-dicarbonyl compound, methylglyoxal, and amino acids. Our results showed that this reaction generated yellow fluorescent products as formed in some glycated proteins. In addition, three types of free radical species were also produced, and their structures were determined by EPR spectroscopy. These free radicals are 1) the cross-linked radical cation, 2) the methylglyoxal radical anion as the counterion, and 3) the superoxide radical anion produced only in the presence of oxygen. The generation of the cross-linked radical cations and the methylglyoxal radical anions does not require metal ions or oxygens. These results indicate that dicarbonyl compounds cross-link free amino groups of protein by forming Schiff bases, which donate electrons directly to dicarbonyl compounds to form the cross-linked radical cations and the methylglyoxal radical anions. Oxygen can accept an electron from the radical anion to generate a superoxide radical anion, which can initiate damaging chain reactions. Time course studies suggest that the cross-linked radical cation is a precursor of yellow fluorescent glycation end products.

Endogenous intracellular glutathionyl radicals are generated in neuroblastoma cells under hydrogen peroxide oxidative stress

We report the detection of endogenous intracellular glutathionyl (GS.) radicals in the intact neuroblastoma cell line NCB-20 under oxidative stress. Spin-trapping and electron paramagnetic resonance (EPR) spectroscopic methods were used for monitoring the radicals. The cells incubated with the spin trap 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) were challenged with H2O2 generated by the enzymic reaction of glucose/glucose oxidase. These cells exhibit the EPR spectrum of the GS. radical adduct of DMPO (DMPO-.SG) without exogenous reduced glutathione (GSH). The identity of this radical adduct was confirmed by observing hyperfine coupling constants identical to previously reported values in in vitro studies, which utilized known enzymic reactions, such as horseradish peroxidase and Cu/Zn superoxide dismutase, with GSH and H2O2 as substrates. The formation of the GS. radicals required viable cells and continuous biosynthesis of GSH. No significant effect on the resonance amplitude by the addition of a membrane-impermeable paramagnetic broadening agent indicated that these radicals were located inside the intact cell. N-Acetyl-L-cysteine (NAC)-treated cells produced NAC-derived free radicals (NAC.) in place of GS. radicals. The time course studies showed that DMPO-.SG formation exhibited a large increase in its concentration after a lag period, whereas DMPO-NAC. formation from NAC-treated cells did not show this sudden increase. These results were discussed in terms of the limit of antioxidant enzyme defenses in cells and the potential role of the GS. radical burst in activation of the transcription nuclear factor NF-kappa B in response to oxidative stress.

Surgery for seizure-related structural lesions of the brain with intraoperative acute recording(ECoG) and functional mapping

Epilepsy surgery has been demonstrated to be an effective alternative treatment for intractable partial or localization related epilepsy. Primary intracranial neoplasms and other structural lesions of the brain are important etiological factors in patients with partial seizure disorders. A neuroimaging identified lesion in patients with seizures, not necessarily medically refractory, may also be an indication for surgery in selected patients. Twelve patients operated on under local or general anesthesia for resection surgery underwent intraoperative recording(electrocorticogram) and/or functional mapping by electrical stimulation or somatosensory evoked potentials-(SSEPs) for identification of the secondary epileptogenic area and/or functional area; 2 meningiomas, 5 astrocytomas, 1 gangliocytoma, 1 abscess, 1 small AVM, 1 cysticercosis and one gliosis by previous intracerebral hemorrhage with middle cerebral artery(MCA) aneurysm. Among these, additional corticectomy or anterior temporal lobectomy was performed in eleven patients. All the patients did well after surgery with good outcomes as seizure free in nine(75%) out of 12 patients with 11.9 months of follow-up period, without any neurological deficits. Intraoperative recording and functional mapping of adjacent areas of the structural lesions of the brain are useful in surgery and can guide the extent of further resection.

On the protective mechanism of the thiol-specific antioxidant enzyme against the oxidative damage of biomacromolecules

A thiol-specific antioxidant enzyme (TSA), which provides protection against the inactivation of other enzymes by the thiol/Fe(III)/oxygen system, was previously isolated and cloned. We investigated the mechanism by which TSA protects biomolecules from oxidative damage caused by the thiol-containing oxidation system using the spin trapping method with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Thiyl radicals from dithiothreitol (.DTT) were produced by horseradish peroxidase/H2O2 under aerobic and anaerobic conditions and by the Fe(III)/oxygen system. The formation of DMPO-.DTT radical adducts were inhibited by TSA regardless of the thiyl radical-generating conditions used. The active mutant C170S also quenched the signals of the radical adduct, whereas the inactive mutant C47S did not exert any effect. It was also found that C170S has a higher rate at the initial stage of the reaction than that of the native enzyme, although C170S failed to remove DMPO-.DTT radical adducts completely. These results indicate that only active TSA can catalyze the removal of thiyl radicals, and cysteine 47 is required for this activity. In addition, thiyl radicals react with oxygen to generate unidentified thiylperoxy species. Fe.EDTA reacts with this species to generate a reactive radical that can abstract hydrogen atom from ethanol to produce a hydroxyethyl radical. This reactive thiyl-oxygen radical is believed to be responsible for causing deleterious effects on biomolecules. Together, our data indicate that TSA protects biomolecules from oxidative damage by catalyzing the removal of thiyl radicals before they generate more reactive radicals. However, presently we cannot rule out the possibility that TSA can also use other thiol-containing species as substrates.

Enzyme function of copper, zinc superoxide dismutase as a free radical generator

The peroxidative activity of Cu,Zn-containing superoxide dismutase (Cu, Zn-SOD) was studied by using a chromogen, 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) which reacts with .OH radicals to form ABTS+, and the spin traps, N-tert-butyl-alpha-phenylnitrone (PBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The formation of ABTS+. in this study required both active Cu,Zn-SOD and H2O2 and followed first order kinetics with respect to SOD and H2O2. However, it showed a binding isotherm with ABTS that yielded a dissociation constant of ABTS-enzyme as Kd = 7.1 +/- 0.5 microM. The Kd values for DMPO and PBN were obtained as 0.63 and 11 mM, respectively, by competition reactions. A radical scavenger, formate anion, inhibits the formation of ABTS+., whereas ethanol does not. The results together indicate that DMPO and anionic scavengers have easy access inside the positively charged active channel of Cu,Zn-SOD and are thus in a position to intercept the newly formed .OH radicals. PBN and ethanol, however, stay outside of the channel and are not able to compete with ABTS for .OH radicals. We trapped free radicals, which were produced in the presence of free radical scavengers, with PBN. The formation curve of PBN-hydroxyethyl radical adduct observed in the presence of ethanol indicated that the enzyme became inactivated in a relatively short period. In contrast, in the presence of anionic scavenger formate, formyl radicals were produced catalytically, and the enzyme activity was protected by the formate against H2O2 inactivation. Thus Cu,Zn-SOD behaves as an enzyme that catalyzes the formation of free radicals using anionic scavengers and H2O2 as substrates.

Copper, zinc superoxide dismutase catalyzes hydroxyl radical production from hydrogen peroxide

Cu,Zn superoxide dismutase (Cu,Zn-SOD; EC 1.15.1.1) is known to be inhibited slowly by H2O2. Using EPR and the spin traps 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN), we have shown that Cu,Zn-SOD catalyzes the formation of "free" .OH radicals from H2O2 in pH 7.6 bicarbonate buffer. Supporting evidence includes the following: (i) H2O2 and active Cu,Zn-SOD are required to yield significant signals from spin-trap-OH adducts. (ii) With O2-., Cu,Zn-SOD causes the appearance of intense resonance signals due to DMPO-OH adducts. These signals were inhibited strongly by catalase. (iii) With H2O2, Cu,Zn-SOD, and DMPO, radical scavengers formate and azide, but not ethanol, decrease DMPO-OH signals while causing new intense signals due to their corresponding DMPO-radical adducts. Failure of ethanol to quench DMPO-OH signals is discussed in light of the positively charged active channel of the enzyme. (iv) With PBN as a spin trap, ethanol quenches .OH radical signals and yields PBN-trapped hydroxyethyl radical signals. (v) Mn-SOD does not catalyze "free" .OH radical formation and it also exerts no effect on the signals of DMPO-OH adducts when added together with the Cu,Zn-SOD. The capacity of Cu,Zn-SOD to generate "free" .OH radicals from H2O2 may in part explain the biological damage associated with elevated intracellular SOD activity.

Manganese(II) catalyzes the bicarbonate-dependent oxidation of amino acids by hydrogen peroxide and the amino acid-facilitated dismutation of hydrogen peroxide

In bicarbonate/CO2 buffer, Mn(II) and Fe(II) catalyze the oxidation of amino acids by H2O2 and the dismutation of H2O2. As the Mn(II)/Fe(II) ratio is increased, the yield of carbonyl compounds per mole of leucine oxidized is essentially constant, but the ratio of alpha-ketoisocaproate to isovaleraldehyde formed increases, and the fraction of H2O2 converted to O2 increases. In the absence of Fe(II), the rate of Mn(II)-catalyzed leucine oxidation is directly proportional to the H2O2, Mn(II), and amino acid concentrations and is proportional to the square of the HCO3- concentration. The rate of Mn(II)-catalyzed O2 production in the presence of 50 mM alanine or leucine is about 4-fold the rate observed in the absence of amino acids and accounts for about half of the H2O2 consumed; the other half of the H2O2 is consumed in the oxidation of the amino acids. In contrast, O2 production is increased nearly 18-fold by the presence of alpha-methylalanine and accounts for about 90% of the H2O2 consumed. The data are consistent with the view that H2O2 decomposition is an inner sphere (cage-like) process catalyzed by a Mn coordination complex of the composition Mn(II), amino acid, (HCO3-)2. Oxidation of the amino acid in this complex most likely proceeds by a free radical mechanism involving hydrogen abstraction from the alpha-carbon as a critical step. The results demonstrate that at physiological concentrations of HCO3- and CO2, Mn(II) is able to facilitate Fenton-type reactions.

Manganese(II)-bicarbonate-mediated catalytic activity for hydrogen peroxide dismutation and amino acid oxidation: detection of free radical intermediates

To examine the structural identities of reactive free radicals and the mechanism of the oxidative modification of proteins, we used EPR and spin-trapping methods to investigate the oxidation of amino acids by H2O2 as well as the decomposition of H2O2 itself catalyzed by Mn(II) ions. Superoxide and hydroxyl radicals (O2-. and OH.) were trapped by a spin trap, 5,5-dimethyl-1-pyrroline-1-oxide (DMPO), in a reaction mixture containing Mn(II) and H2O2 in bicarbonate/CO2 buffer. When Hepes was used in place of bicarbonate buffer, superoxide radical was not observed, indicating the importance of bicarbonate buffer. With addition of L-leucine to a similar reaction mixture, a leucine-derived radical that replaced the DMPO-superoxide adduct was detected in the absence and presence of DMPO. Using various isotope-enriched L-leucines, we successfully identified this radical as a hydronitroxide, -OOC(R)CHNHO.. The data are consistent with the formation of a transient "caged" OH. in the inner coordination sphere of Mn(II). This caged OH. is likely to undergo an intramolecular hydrogen-atom abstraction from the Mn-bound H2O2 or amino acid. Two reaction schemes are proposed to account for the experimental results shown here and in the preceding papers.

Neutral metal-bound water is the base catalyst in liver alcohol dehydrogenase

The catalytic role of the active site metal-water complex in horse liver alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) is investigated on the basis of a comparative analysis of the pH dependence of steady-state kinetic parameters of the native and active-site-specific Co2+-reconstituted enzyme and on the basis of assignment of the coordination environment of the Co2+ by electron paramagnetic resonance methods. The pH dependence of the kinetic parameters for the oxidation of benzyl alcohol reveals two ionizations (pK1 approximately equal to 6.7; pK2 approximately equal to 10.6) that govern kcat and belong to the ternary enzyme-NAD+-alcohol complex and two ionizations (pK1' approximately equal to 7.5; pK2' approximately equal to 8.9) that govern kcat/Km and belong to the binary enzyme-NAD+ complex. The ionizations pK2 and pK2' decrease by 0.5-1 pK alpha unit upon replacement of the active site Zn2+ by Co2+. A similar metal ion dependence of pK2 and pK2' is observed for the oxidation of 2-propanol. We attribute these ionizations to a metal-bound water molecule. The zero-field splitting energy of the Co2+ in the binary enzyme-NADH complex and the ternary enzyme-NADH-CF3CH2OH complex is approximately equal to 22 cm-1, indicative of a pentacoordinate species. Binding of a water molecule to the metal ion as the fifth ligand in the ternary enzyme-NADH-CF3CH2OH complex is confirmed on the basis of magnetic interactions of H2(17)O with Co2+. The results indicate that the active site metal ion in catalytically competent ternary enzyme-coenzyme-substrate complexes is pentacoordinate and is ligated by a neutral water molecule in the physiological pH range. We suggest that the neutral metal-bound water molecule serves as the base catalyst for proton abstraction in alcohol oxidation.

Coordination environment of the active-site metal ion of liver alcohol dehydrogenase

The coordination environment of the catalytically active metal ion of horse liver alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) has been investigated by electron paramagnetic resonance (EPR) methods with use of the active-site-specific Co2+-reconstituted enzyme. The EPR absorption spectrum of the metal-substituted enzyme is characteristic of a rhombically distorted environment. The spectrum of the enzyme--NAD+ complex shows approximate axial symmetry of the metal ion site, indicating that binding of the coenzyme induces a structural alteration in the active-site region. This environment is not significantly altered further by binding of the competitive inhibitor pyrazole. To assign the coordination number of the active-site metal ion, the zero-field splitting was determined on the basis of the temperature dependence of the spin--lattice relaxation of the Co2+ ion. The zero-field splitting energies are approximately 9 cm-1 for the free Co2+-reconstituted enzyme and approximately 46 and approximately 47 cm-1 for the enzyme--NAD+ and enzyme--NAD+--pyrazole complex, respectively. On the basis of studies of structurally defined small molecule complexes, these values are compatible with a tetracoordinate metal ion in the active site of the free enzyme but a pentacoordinate metal ion in the binary enzyme--NAD+ complex and in the ternary enzyme--NAD+--inhibitor complex and, therefore, presumably also in the catalytically active ternary enzyme--NAD+--alcohol complex formed in the course of alcohol oxidation.