Role of skin prick test and serological measurement of specific IgE in the diagnosis of occupational asthma resulting from exposure to vinyl sulphone reactive dyes

OBJECTIVES

Some patients with occupational asthma resulting from exposure to reactive dyes have skin reactivity to the causative dyes and specific IgE to reactive dyes have been found in these patients. However, the usefulness of skin prick tests (SPTs) and serological measurement of specific IgE in screening, diagnosis, and monitoring the occupational asthma resulting from exposure to reactive dyes have not yet been assessed. In this study, the clinical validation of SPTs and measurement of specific IgE to vinyl sulphone reactive dyes by enzyme linked immunosorbent assay (ELISA) was evaluated.

METHODS

42 Patients with occupational asthma from reactive dyes (true positive group) were enrolled. In these the causative reactive dye was confirmed by bronchial challenge test. 93 Asymptomatic factory workers with negative challenge to the reactive dye (true negative group) and 16 unexposed controls with negative challenge to the reactive dye were also enrolled. Skin prick tests were done with 10 mg/ml reactive dye in 0.4% phenol/0.9% saline. IgE specific to reactive dye conjugated to human serum albumin (HSA) was measured with enzyme linked immunosorbent assays (ELISAs).

RESULTS

None of the unexposed controls had a positive response to SPTs. The sensitivity (76.2% v 53.7%), specificity (91.4% v 86.0%), positive predictive value (80.0% v 62.9%), and negative predictive value (89.5% v 80.8%) of SPTs were higher than those of ELISAs. The mean weal size of reaction to reactive dye was weakly correlated with the ELISA optical density of IgE to reactive dye conjugate in patients with occupational asthma from reactive dyes (n=41, r=0.337, p<0.05). In four patients with occupational asthma from reactive dyes and eight control subjects exposed to reactive dye, IgE specific to reactive dye conjugated to HSA was detected with ELISA even though they showed negative skin reactivity. Six patients completely avoided the reactive dye for a mean (SD) 27.8 (10.3) months, IgE specific to reactive dyes decreased in all six patients (p<0.05) during this time.

CONCLUSIONS

Both SPTs and detection of IgE specific to reactive dye in serum samples could be valuable for screening, diagnosis, and monitoring occupational asthma resulting from exposure to reactive dyes. These two tests would complement each other.

Clinical application of computer-aided rapid prototyping for tooth transplantation

The maintenance of healthy periodontal ligament cells in the donor tooth is one of the most important factors for successful tooth transplantation. This is achieved by minimizing the extraoral time during the surgical procedure. If a duplicate form of donor tooth could be obtained before extraction, it would be possible to precontour the recipient alveolar bone compatible with the donor tooth, and thereby reduce the extra-oral time of the donor tooth. We obtained a three-dimensional image with the real dimensions of the donor tooth from a CT Highspeed Advantage, allowing a life-sized resin model of the tooth to be fabricated. From 22 clinical cases, we achieved an average total transplantation time of 7.7 min. The average distance between the transplanted root surface and the alveolar bone from 12 available cases was 0.87 mm at the mesial cervix, 0.91 mm at the mesial apex, 0.98 mm at the distal cervix and 1.16 mm at the distal apex on the postoperative radiographs. Clinical data indicate that computer-aided rapid prototyping may be of value in minimizing the extra-oral time and possible injury to transplanted tooth during the process of autotransplantation.

The alteration of gamma-aminobutyric acid-transaminase expression in the gerbil hippocampus induced by seizure

It is well established that GABA degradation may play a key role in epileptogenesis. However, whether or not the expression of GABA-transaminase (GABA-T), which catalyzes GABA degradation and participates in the neuronal metabolism via GABA shunt, changes chronologically after on-set of seizure remains to be clarified. To identify the change of GABA-T expression in seizure, GABA-T expression in the gerbil hippocampus, associated with different sequelae of spontaneous seizures, was investigated. The distribution pattern of GABA-T immunoreactive neurons in the hippocampus between the seizure-resistant and pre-seizure group of seizure sensitive gerbils was similar. Interestingly, at 30 min postictal, the enhancement of GABA-T immunoreactivity in the perikarya was apparently observed. This contrasted with the decline in GABA-T immunoreactivity in the granular and pyramidal layer. At 12-24 h postictal, GABA-T immunoreactivity in the hilar neurons had declined significantly. However, the GABA-T immunoreactivity in the granular layer increased. These findings suggest that in the gerbil, the alteration in GABA-T expressions may play an important role in the self-recovery mechanism from seizure attack via both GABA degradation and regulation of neuronal metabolism.

Glutathione S-transferase mu modulates the stress-activated signals by suppressing apoptosis signal-regulating kinase 1

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase that can activate the c-Jun N-terminal kinase and the p38 signaling pathways. It plays a critical role in cytokine- and stress-induced apoptosis. To further characterize the mechanism of the regulation of the ASK1 signal, we searched for ASK1-interacting proteins employing the yeast two-hybrid method. The yeast two-hybrid assay indicated that mouse glutathione S-transferase Mu 1-1 (mGSTM1-1), an enzyme involved in the metabolism of drugs and xenobiotics, interacted with ASK1. We subsequently confirmed that mGSTM1-1 physically associated with ASK1 both in vivo and in vitro. The in vitro binding assay indicated that the C-terminal portion of mGSTM1-1 and the N-terminal region of ASK1 were crucial for binding one another. Furthermore, mGSTM1-1 suppressed stress-stimulated ASK1 activity in cultured cells. mGSTM1-1 also blocked ASK1 oligomerization. The ASK1 inhibition by mGSTM1-1 occurred independently of the glutathione-conjugating activity of mGSTM1-1. Moreover, mGSTM1-1 repressed ASK1-dependent apoptotic cell death. Taken together, our findings suggest that mGSTM1-1 functions as an endogenous inhibitor of ASK1. This highlights a novel function for mGSTM1-1 insofar as mGSTM1-1 may modulate stress-mediated signals by repressing ASK1, and this activity occurs independently of its well-known catalytic activity in intracellular glutathione metabolism.

Identification of the modifying sites of mono-PEGylated salmon calcitonins by capillary electrophoresis and MALDI-TOF mass spectrometry

A capillary electrophoretic method (CE) was developed for the determination of the PEG-modification sites of three positional isomers of mono-PEG modified salmon calcitonins (mono-PEG-sCTs). Resistance to proteolytic degradation on the PEG modification sites resulted in different patterns of CE electropherograms for the tryptic digested mono-PEG-sCTs isomers, and the PEG modification sites were assigned accordingly. The PEG-modification sites were also confirmed directly by determining the molecular masses of the tryptic digested PEG-modified fragments of respective mono-PEG-sCT by the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry.

Research on annihilation of cancer cells by glass-ceramics for cancer treatment with external magnetic field. I. Preparation and cytotoxicity

Ferrimagnetic glass-ceramics were prepared as a heating mediator for hyperthermia in cancer treatment. We prepared glasses in the system 40Fe2O3-30CaO-30SiO2 and precipitated ferrimagnetic crystallites through controlled two-step heat treatment. To improve the heating capability of ferrimagnetic crystallites, i.e., magnetite, generation of other crystalline phases should be prohibited. The addition of each 1% of P2O5 and B2O3 led to lowering the crystallization temperature of magnetite, which was useful to suppress the other crystalline formation. The maximum nucleating and crystal growth rates were 20.47 x 10(6)/mm2 x s at 690 degrees C and 8.125 nm/min(0.5) at 940 degrees C, respectively. After nucleation at 690 degrees C for 60 min prior to crystal growth at 940 degrees C for 2 h, samples exhibited the following properties: crystallite size of 90.5 nm, the maximum volumetric fraction of 31.1%, and saturation magnetization of 100 emu/cm2. The coercive forces were ranged between 382.0 and 388.2 Oe in all heat-treatment conditions. As a result of a preclinical evaluation of biocompatibility by agar diffusion test with L929 cells, both as-quenched and heat-treated glasses could be biocompatible.

Hepatic capsular retraction: unusual finding of cavernous hemangioma

We report a case of hepatic giant hemangioma, which showed hepatic capsular retraction on CT and MRI. Pathologic examination revealed fibrosis combined with hemangioma, especially in a subcapsular location, which was responsible for the capsular retraction.

Brain succinic semialdehyde dehydrogenase: identification of reactive lysyl residues labeled with pyridoxal-5'-phosphate

An NAD+ dependent succinic semialdehyde dehydrogenase from bovine brain was inactivated by pyridoxal-5'- phosphate. Spectral evidence is presented to indicate that the inactivation proceeds through formation of a Schiff's base with amino groups of the enzyme. After NaBH(4) reduction of the pyridoxal-5'-phosphate inactivated enzyme, it was observed that 3.8 mol phosphopyridoxyl residues were incorporated/enzyme tetramer. The coenzyme, NAD+, protected the enzyme against inactivation by pyridoxal-5'-phosphate. The absorption spectrum of the reduced and dialyzed pyridoxal-5'-phosphate-inactivated enzyme showed a characteristic peak at 325 nm, which was absent in the spectrum of the native enzyme. The fluorescence spectrum of the pyridoxyl enzyme differs completely from that of the native enzyme. After tryptic digestion of the enzyme modified with pyridoxal-5'-phosphate followed by [3H]NaBH4 reduction, a radioactive peptide absorbing at 210 nm was isolated by reverse-phase HPLC. The sequences of the peptide containing the phosphopyridoxyllysine were clearly identical to sequences of other mammalian succinic semialdehyde dehydrogenase brain species including human. It is suggested that the catalytic function of succinic semialdehyde dehydrogenase is modulated by binding of pyridoxal-5'-phosphate to specific Lys(347) residue at or near the coenzyme-binding site of the protein.

Analysis of radiation workers' dose records in the Korean National Dose Registry

Data are presented on the externally received personal dose equivalent for radiation workers who used the Korea Radioisotope Association's personal monitoring and dose record keeping service since 1984, and provide initial statistics on Korean workers who have been exposed to ionising radiation in different occupations. The total number of workers registered during the period of 1984 to 1999 was 64,518. The number increased steadily and the accumulated dose also increased. The proportion of radiation workers by occupation was 38.4% for nuclear power plants, 20.3% for industrial organisations and 12.4% for non-destructive industry. The annual collective dose of radiation workers was 31.72 man.Sv in 1999. The mean annual dose by sex was 1.49 mSv for males and 0.56 mSv for females and the mean annual dose for a worker was 1.41 mSv with the highest mean dose being received by non-destructive industry (3.53 mSv). Very few workers (0.8%) received more than 20 mSv (2 rem) and only one more than 50 mSv, the legal limit for an annual dose increase. There has been a steady decline in the mean dose since 1984, showing a significant decrease in dose with time (p<0.001). The data showed that radiation protection in Korea was improving, though annual doses were still higher than other countries.

Efficient intracellular delivery of GFP by homeodomains of Drosophila Fushi-tarazu and Engrailed proteins

The 60 amino acid long homeodomain of Antennapedia (Antp), either alone or as a fusion protein with 30-40 amino acid long foreign polypeptides, has been reported to cross biological membranes by an energy- and receptor-protein-independent mechanism. Moreover, the 16 amino acid long third helix of the Antp homeodomain, so-called penetratin, possesses translocation properties when fused to fewer than 100 amino acids as well. These findings led us to study whether such a protein tansduction property is shared by other homeodomains. We report here that homeodomains of two homeoproteins, Fushi-tarazu and Engrailed, are able to transduce a 238 amino acid long green fluorescent protein into cultured cells as efficiently as other well-known protein transduction domains, such as an internal oligopeptide of Tat and penetratin. These findings suggest that such transduction activity of homeodomains might have some physiological roles and that it can be exploited for development of efficient transduction vectors for research use and protein therapy.

Comparative studies on the distribution of glutamate transporters in the retinae of the Mongolian gerbil and the rat

Glutamate is the major excitatory amino acid transmitter in vertebrate retinae. Glutamate transporters therefore play an important role in the precise control of glutamate concentration in the synaptic cleft by regulating extracellular glutamate concentration. In the present study, we performed an analysis of the expressions of three glutamate transporters in gerbil retina using immunohistochemistry. In the gerbil retina, excitatory amino acid carrier 1 and glutamate transporter 1 immunoreactivity was predominant in the ganglion cells but not amacrine or bipolar cells. Glutamate/aspartate transporter (GLAST) immunoreactivity was observed in the radial gliocytes of which the dense network of fine processes was localized in the inner and outer plexiform layers. GLAST immunoreactivity was also detected in astrocytes in the nerve fibre layer. These results demonstrate that three glutamate transporters show specific distributions in the gerbil retina and suggest that the glutamate re-uptake system in the gerbil retina may be different from that of the rat.

Oxidative modification and inactivation of Cu,Zn-superoxide dismutase by 2,2'-azobis(2-amidinopropane) dihydrochloride

We have investigated oxidative modification of human Cu, Zn-superoxide dismutase (SOD) by alkylperoxyl radicals and alkylperoxides. To generate free radicals, we used the hydrophilic azocompound, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). When Cu,Zn-SOD was incubated with AAPH, the enzyme activity was decreased gradually in a time-dependent manner. The oxidative damage to Cu,Zn-SOD by AAPH-derived radicals led to protein fragmentation which is associated with the inactivation of enzyme. Incubation with AAPH resulted in the release of copper ions from Cu,Zn-SOD and the generation of protein carbonyl derivatives. Catalase did not protect the fragmentation of Cu,Zn-SOD whereas azide, glutathione and a metal chelator, diethylenetriamine pentaacetic acid inhibited the protein fragmentation. When Cu,Zn-SOD that has been exposed to AAPH was subsequently analyzed by amino acid analysis, lysine, histidine, proline, and valine residues were particularly sensitive. It is suggested that oxidative damage of Cu,Zn-SOD by AAPH-derived radicals may induce the perturbation of cellular antioxidant defense systems and subsequently lead to the deleterious condition in cells.

Transduction of Cu,Zn-superoxide dismutase mediated by an HIV-1 Tat protein basic domain into mammalian cells

A human Cu,Zn-superoxide dismutase (Cu,Zn-SOD) gene was fused with a gene fragment encoding the nine amino acid transactivator of transcription (Tat) protein transduction domain (RKKRRQRRR) of HIV-1 in a bacterial expression vector to produce a genetic in-frame Tat-SOD fusion protein. The expressed and purified Tat-SOD fusion protein in Escherichia coli can enter HeLa cells in a time- and dose-dependent manner when added exogenously in a culture media. Denatured Tat-SOD protein was transduced much more efficiently into cells than were native proteins. Once inside the cells, transduced Tat-SOD protein was enzymatically active and stable for 24 h. The cell viability of HeLa cells treated with paraquat, an intracellular superoxide anion generator, was increased by transduced Tat-SOD. These lines of results suggest that the transduction of Tat-SOD fusion protein may be one of the ways to replenish the Cu,Zn-SOD in the various disorders related to this antioxidant enzyme.

Elevation of the gamma-aminobutyric acid transaminase expression in the gerbil CA1 area after ischemia-reperfusion damage

gamma-Aminobutyric acid-transaminase (GABA-T) plays an important role in the metabolism of GABA, particularly in the neurons or glial cells. The present study was undertaken to determine the alteration of GABA-T expression in the gerbil hippocampus after ischemia-reperfusion. In the sham, GABA-T(+) neurons were scattered in the hippocampus proper and dentate gyrus. The intensity of the GABA-T immunoreactivity had nearly disappeared in the interneurons at 12 h after ischemia. In contrast, 24 h post-ischemia the dramatic augmentation of GABA-T immunoreactivity in the pyramidal cells was observed in the CA1 area but not in the CA2 or CA3 areas. Forty-eight hours after ischemia-reperfusion, its immunoreactivity was preserved in the CA1 neurons. These results suggest that the over-expression of GABA-T in the CA1 area may be related to delayed neuronal death after ischemia-reperfusion insult.

Capsaicin inhibits platelet-activating factor-induced cytosolic Ca2+ rise and superoxide production

Platelet-activating factor (PAF) is an important participant in the inflammatory process. We studied the regulation of PAF activity by capsaicin in human promyelocytic leukemia HL-60 cells. Capsaicin inhibited PAF-induced superoxide production in a concentration-dependent manner. In addition to PAF, the fMLP- and extracellular ATP-induced superoxide productions were inhibited by capsaicin, whereas PMA-induced superoxide production was not affected. In the PAF-stimulated cytosolic Ca2+ increase, capsaicin inhibited in particular the sustained portion of the raised Ca2+ level without attenuation of the peak height. In the absence of extracellular Ca2+, the PAF-induced Ca2+ elevation was not inhibited by capsaicin because capsaicin only inhibited the Ca2+ influx from the extracellular space. In addition, capsaicin did not affect PAF-induced inositol 1,4,5-trisphosphate production, suggesting that phospholipase C activation by PAF is not affected by capsaicin. Store-operated Ca2+ entry (SOCE) induced by thapsigargin was inhibited by capsaicin in a concentration-dependent manner. This capsaicin effect was also observed on thapsigargin-induced Ba2+ and Mn2+ influx. Furthermore, capsaicin's inhibitory effect on the thapsigargin-induced Ca2+ rise overlapped with that of SK&F96365, an inhibitor of SOCE. Both capsaicin and SK&F96365 also inhibited PAF-induced cytosolic superoxide generation in HL-60 cells differentiated by all-trans-retinoic acid. Our data suggest that capsaicin exerts its anti-inflammatory effect by inhibiting SOCE elicited via PLC activation, which occurs upon PAF activation and results in the subsequent superoxide production.

Human brain GABA transaminase tissue distribution and molecular expression

Human brain gamma-aminobutyrate transaminase is differentially expressed in a tissue-specific manner. mRNA master dot-blot analysis for 50 different human tissues, including different brain regions and fetal tissues, provided a complete map of the tissue distribution. Genomic Southern analysis revealed that the gamma-aminobutyrate transaminase gene is a single copy, at least 15 kb in size. In addition, human brain gamma-aminobutyrate transaminase cDNA was expressed in Escherichia coli using a pGEX expression vector system. Catalytically active gamma-aminobutyrate transaminase was expressed in large quantities and the purified recombinant enzyme had kinetic parameters that were indistinguishable from those isolated from other mammalian brains. The human enzyme was inactivated by a well-known antiepileptic drug vigabatrin. Values of Ki and kinact were 1 mM and 0.35 min-1, respectively. Results from inactivation kinetics suggested that human gamma-aminobutyrate transaminase is more sensitive to the vigabatrin drug than the enzyme isolated from bovine brain.

Human pyridoxal kinase: overexpression and properties of the recombinant enzyme

Pyridoxal kinase catalyses the phosphorylation of the vitamin B6. A human brain pyridoxal kinase cDNA was isolated, and the recombinant enzyme was overexpressed in E. coli as a fusion protein with maltose binding protein (MBP). Pure pyridoxal kinase exhibits a molecular mass of about 40 kDa when examined by SDS-PAGE and FPLC gel filtration. The recombinant enzyme is a monomer endowed with catalytic activity, indicating that the native quaternary structure of pyridoxal kinase is not a prerequisite for catalytic function. Zn2+ is the most effective divalent cation in the phosphorylation of pyridoxal, and the human enzyme has maximum catalytic activity in the narrow pH range of 5.5-6.0. The Km values for two substrates pyridoxal and ATP are 97 microM and 12 microM, respectively. In addition, the unfolding processes of the recombinant enzyme were monitored by circular dichroism. The values of the free energy change of unfolding (AGo = 1.2 kcal x mol(-1) x K(-1)) and the midpoint transition (1 M) suggested that the enzyme is more stable than ovine pyridoxal kinase against denaturation by guanidine hydrochloride. Intrinsic fluorescence spectra of the human enzyme from red-edge excitation and fluorescence quenching experiments showed that the tryptophanyl residues are not completely exposed and more accessible to neutral acrylamide than to the negatively charged iodide. The first complete set of catalytic and structural properties of human pyridoxal kinase provide valuable information for further biochemical studies on this enzyme.

Anticonvulsant compounds from the wood of Caesalpinia sappan L

80% Aqueous MeOH extracts from the wood of Caesalpinia sappan, which showed remarkable anticonvulsant activity, were fractionated using EtOAc, n-BuOH, and H2O. Among them, the EtOAc fraction significantly inhibited the activities of two GABA degradative enzymes, succinic semialdehyde dehydrogenase (SSADH) and succinic semialdehyde reductase (SSAR). Repeated column chromatographies for the fraction guided by activity test led to the isolation of the two active principal components. Their chemical structures were determined to be sappanchalcone and brazilin based on spectral data. The pure compounds, sappanchalcone (1) and brazilin (2), inactivated the SSAR activities in a dose dependent manner, whereas SSADH was inhibited partially by sappanchalcone and not by brazilin.

Effect of iron state on crystallization and dissolution in Fe2O3-CaO-SiO2 glasses

The possibility of iron-containing glasses as thermoseeds for hyperthermia of bone tumor was reported previously. There is, however, no report about the effect of iron state on the crystallization of magnetite and the resultant properties. The iron states were determined by Mössbauer spectroscopy in Fe2O3-CaO-SiO2 system. It was found that the higher CaO content interrupts the crystallization of magnetite crystallites as well as the oxidation of iron, that is, the transformation from Fe3+ to Fe2+. A sample containing large amounts of Fe2+ showed the faster increment of temperature when the alternating magnetic field was applied. In order to use the thermoseed for a hyperthermia, we can say that the composition with low CaO content is most useful.

Truncated form of importin alpha identified in breast cancer cell inhibits nuclear import of p53

Disruption of the function of tumor suppressor proteins occasionally can be dependent on their subcellular localization. In about 40% of the breast cancer tissues, p53 is found in the cytoplasm as opposed to the nucleus, where it resides in normal breast cells. This means that the regulation of subcellular location of p53 is an important mechanism in controlling its function. The transport factors required for the nuclear export of p53 and the mechanisms of their nuclear export have been extensively characterized. However, little is known about the mechanism of nuclear import of p53. p53 contains putative nuclear localization signals (NLSs) which would interact with a nuclear transport factor, importin alpha. In this report we demonstrate that importin alpha binds to NLSI in p53 and mediates the nuclear import of p53. Reverse transcriptase-polymerase chain reaction and sequencing analyses showed that a truncated importin alpha deleted the region encoding the putative NLS-binding domain of p53, suggesting that it could not bind to NLSs of p53 proteins. Binding of importin alpha to p53 was confirmed by using yeast two-hybrid assay. When expressed in CHO-K1 cells, the truncated importin alpha predominantly localized to the cytoplasm. In truncated importin alpha expressing cells, p53 preferentially localized to cytoplasmic sites as well. A significant increase in the p21(waf1/cip1) mRNA level and induction of apoptosis were also observed in importin alpha overexpressing cells. These results strongly suggest that importin alpha functions as a component of the NLS receptor for p53 and mediates nuclear import of p53.

Identification of three novel mutations and a high frequency of the Arg778Leu mutation in Korean patients with Wilson disease

Four mutations--R778L, A874V, L1083F, and 2304delC--in the copper-transporting enzyme, P-type ATPase (ATP7B), were identified in Korean Patients with Wilson disease. Arg778Leu, the most frequently reported mutation of this enzyme, was found in six of eight unrelated patients studied, an allele frequency of 37.5%, which is considerably higher than those in other Asian populations. The novel single nucleotide deletion, 2304delC, was found in one patient. Since a mutation at cDNA nucleotide 2302 (2302insC) had been previously described, this region of the ATP7B gene may be susceptible to gene rearrangements causing Wilson disease.

Surface ultrastructure of Metagonimus takahashii metacercariae and adults

A scanning electron microscopic study was performed on the surface ultrastructure of metacercariae and adults of Metagonimus takahashii. Metacercariae were collected from the scale of crucian carp (Carassius auratus), and adult flukes were harvested 1-4 weeks after infection to rats. In excysted metacercariae, the oral sucker had type I (numerous) and type II (seven in total) sensory papillae. Tegumental spines were dense and digitated into 5-7 points on the surface anterior to the ventral sucker, but became sparse and less digitated posteriorly toward the end of the body. In adults, seven type II sensory papillae were characteristically arranged around the lip of the oral sucker, and on the inner side of the lip four small and two large type I sensory papillae were symmetrically seen on each side (12 in total). Tegumental spines on anterior two-thirds of the body, were digitated with 9-12 tips ventrally and 8-13 tips dorsally. Sperms entering into the Laurer's canal were observed. The results show that the surface ultrastructure of M. takahashii is generally similar to those of M. yokogawai and M. miyatai except for the digitation of tegumental spines.

Regulatory properties of glutamate dehydrogenase from Sulfolobus solfataricus

The purified glutamate dehydrogenase (GDH) from Sulfolobus solfataricus showed remarkable thermostability and retained 90-95% of the initial activity after incubation at -20 degrees C, 4 degrees C, and 25 degrees C for up to 6 months. Unlike mammalian GDHs, the activity of GDH from Sulfolobus solfataricus was not significantly affected by the presence of various allosteric effectors such as ADP, GTP, and leucine. Incubation of GDH with increasing concentration of o-phthalaldehyde resulted in a progressive decrease in enzyme activity, suggesting that the o-phthalaldehyde-modified lysine or cysteine is directly involved in catalysis. The inhibition was competitive with respect to both 2-oxoglutarate (Ki = 30 microM) and NADH (Ki = 100 microM), further supporting a possibility that the o-phthalaldehyde-modified residues may be directly involved at the catalytic site. The modification of GDH by the arginine-specific dicarbonyl reagent phenylglyoxal was also examined with the view that arginine residues might play a general role in the binding of coenzyme throughout the family of pyridine nucleotide-dependent dehydrogenases. The purified GDH was inactivated in a dose-dependent manner by phenylglyoxal. Either NADH or 2-oxoglutarate did not gave any protection against the inactivation caused by a phenylglyoxal. This result indicates that GDH saturated with NADH or 2-oxoglutarate is still open to attack by phenylglyoxal. Phenylglyoxal was an uncompetitive inhibitor (Ki = 5 microM) with respect to 2-oxoglutarate and a noncompetitive inhibitor (Ki = 6 microM) with respect to NADH. The above results suggests that the phenylglyoxal-modified arginine residues are not located at the catalytic site and the inactivation of GDH by phenylglyoxal might be due to a steric hindrance or a conformational change affected by the interaction of the enzyme with its inhibitor.

Fragmentation of human ceruloplasmin induced by hydrogen peroxide

We investigated the fragmentation of human ceruloplasmin induced by H2O2 to study its oxidative damage. When ceruloplasmin was incubated with H2O2, the frequency of the protein fragmentation increased in a proportion to the concentration of H2O2. It also increased in a time-dependent manner and was accompanied by gradual loss of the oxidase activity. Hydroxyl radical scavengers such as azide and mannitol inhibited the fragmentation of ceruloplasmin. The deoxyribose assay showed that hydroxyl radicals were generated in the reaction of ceruloplasmin with H2O2. Incubation of ceruloplasmin with H2O2 resulted in a time-dependent release of copper ions. The released copper ion may participate in a Fenton-like reaction to produce hydroxyl radical, which enhanced the fragmentation. The protection of the fragmentation by copper chelators such as diethylenetriaminepentaacetic acid and bathocuproine indicates a role for copper ion in the reaction. These results suggest that the fragmentation of ceruloplasmin induced by H2O2 is due to hydroxyl radicals formed by a copper-dependent Fenton-like reaction.