Measurement of total nitric oxide metabolite (NO(x)(-)) levels in vivo

The measurement of the total level of nitric oxide (NO) metabolite (NO(x)(-)) by microdialysis has recently been used to assess the production of NO in the in vivo brain [D. Luo, S. Knezevich, S.R. Vincent, N-Methyl-D-aspartate-induced nitric oxide release: an in vivo microdialysis study, Neuroscience, 57 (1993), 897-900; K. Ohta, N. Arai, M. Shibata, J. Hamada, S. Komatsumoto, K. Shimazu, Y. Fukuuchi, A novel in vivo system for consecutive measurement of brain nitric oxide production combined with the microdialysis technique, Neurosci. Lett., 176 (1994), 165-168; K. Shintani, S. Kanba, T. Nakai, K. Sato, G. Yagi, R. Kato, M. Arai, Measurement by in vivo microdialysis of nitric oxide release in the rat cerebellum, J. Psychiatr. Neurosci., 3 (1994), 217-221; H. Togashi, K. Mori, K. Ueno, M. Matsumoto, N. Suda, H. Saito, M. Yoshika, Consecutive evaluation of nitric oxide production after transient cerebral ischemia in the rat hippocampus using in vivo brain microdialysis, Neurosci. Lett., 240 (1998), 53-57]. Although several methods are available for detecting NO(x)(-) levels in dialysates, these methods are either not sensitive enough or require expensive experimental equipment. The method described herein provides a convenient and sensitive procedure for determining NO(x)(-) levels in dialysates. This method is useful for the in vivo study of NO production from various brain regions in various pathological conditions, and can be applied to other tissues.

Relationship between the conserved alpha subunit arginine 107 and effects of phosphate on the activity and stability of Vibrio harveyi luciferase

The Arg107 of the alpha subunit is a conserved residue for all known bacterial luciferases. The phosphate moiety of the reduced flavin mononucleotide (FMNH(2)) side chain has been hypothesized to be anchored at this site (A. J. Fisher, F. M. Raushel, T. O. Baldwin, and I. Rayment Biochemistry 34, 6581-6586, 1995). Mutations of alphaArg107 of the Vibrio harveyi luciferase to alanine, serine, and glutamate were carried out to test such a hypothesis. These variants were characterized and compared with the wild-type luciferase with respect to their K(m) for decanal, FMNH(2), and reduced riboflavin in both low- (0.01 or 0.05 M) and high- (0.3 M) phosphate buffers at pH 7.0. Results are consistent with the hypothesized binding of the FMNH(2) phosphate group by alphaArg107. Moreover, the alphaArg107 residue was apparently important in the expression of the luciferase maximal activity and aldehyde binding. Phosphate ion is also known to have other effects on luciferase stability. We compared the three luciferase variants with the native enzyme with respect to the decay rate of the FMN 4a-hydroperoxide intermediate II, and rates of inactivation by trypsin digestion, modification by N-ethylmaleimide, and heat treatment in low- and high-phosphate buffers. On the basis of patterns of the phosphate effects, alphaArg107 appeared to be important to the enhancement of luciferase stability against trypsin proteolysis at high phosphate but was not involved in regulating the intermediate II decay or sensitivity to N-ethylmaleimide modification. Differential effects of mutations on luciferase thermal stability were observed. It is uncertain whether alphaArg107 is involved in the enhanced thermal stability of the native luciferase in high phosphate buffer.

[Sub-cloning and preliminary sequence analysis of the gene encoding of a cefoperazone hydrolyzing beta-lactamase isolated from Escherichia coli]

Escherichia coli HX88108, which is resistant to cefoperazone(CPZ), was isolated from a severely infected patient. We studied genetical basis of beta-lactamase produced in E. coli HX88108 by pFL25, one of the recombinant plasmid of pFC. Largescale pFL25 plasmid was extracted, purified, and cleaved with restriction endonuclease EcoR I, Sal I, Pvu I, then subcloned into vector pUC19 as 1.9 kb, 0.9 kb, 0.65 kb fragments respectively. Recomminant plasmids were selected by alpha-complementation and determined by restriction endonuclease analysis. DNA sequencing was performed by the dideoxy polymerase chain termination method. Partial nucleotide sequence(1-78 nucleotide position) of the gene was found to be highly homologous (97%) with the gene coding for TEM-52 extended spectrum beta-lactamase of K. pneumonise, suggesting that the beta-lactamase coded by the cefoperazone resistant gene might be derived from TEM-type beta-lactamase.

The contributions of voltage- and time-dependent potassium conductances to the electroretinogram in rabbits

The electroretinogram (ERG) is generated by light-induced electrical activity in retinal cells. Since potassium ions and potassium conductances play a major role in determining the membrane potential of cells, changes in these are expected to affect the amplitude and pattern of the ERG. We recorded the ERG responses and the isolated P-III waves of rabbits after intraocular injections of specific blockers for potassium channels. 4-aminopyridine (4-AP) did not cause any noticeable changes in the ERG while tetraethylammonium chloride (TEA) induced time-dependent effects. Short-term (1-2 h) effects were expressed as significant augmentation of the b-wave with little change in the a-wave. At longer periods of follow-up, the a-wave increased in amplitude while the b-wave decreased. TEA augmented the amplitude of the isolated P-III wave. These effects of TEA can be explained by TEA-induced depolarization of the photoreceptors. Cesium ions and barium ions induced substantial augmentation of the b-wave. Barium but not cesium ions reduced the isolated P-III component of the ERG probably by blocking the potassium channels in the Müller cells. The augmentation of the b-wave by both barium or cesium ions is inconsistent with the Müller cells hypothesis for the ERG b-wave.

Sepsis facilitates brain serotonin activity and impairs learning ability in rats

Sepsis often provokes various neurological disorders. Because many neurologic symptoms are caused by changes in neurotransmissions, we investigated the relationship between behavioral alterations and changes in activities of the monoaminergic systems in rats. Sepsis was induced by cecal ligation and puncture. A step-through passive avoidance test was used for the behavioral evaluation. Passive avoidance retention in animals subjected to learning immediately before the septic or sham operation was examined after 24 or 48 h. Retention performance in animals subjected to learning 24 h after the operation was also examined after a further 24 h. Plasma concentrations of amino acids were determined 24 h after the operation. The activities of the brain monoaminergic systems were evaluated by ratios of metabolites to monoamines. Marked damage was found in the septic rats in the blood analysis 24 h after the operation. The plasma concentrations of tyrosine and arginine in the septic rats were decreased to 69% and 70% of those in the sham-operated animals, respectively. Retention performance was impaired in the septic rats when they were subjected to learning 24 h after the operation, but it was not impaired when animals were subjected to learning before the septic operation. The brain concentration of serotonin was increased in the cerebral cortex, striatum, and hippocampus 48 h after the septic operation, but not after 24 h. The concentration of 5-hydroxyindoleacetic acid, a metabolite of serotonin, was increased in the above three regions both 24 and 48 h after the operation, but not in the hypothalamus. Facilitation of the serotonergic activity in the telencephalon and hippocampus is suggested to be involved in the impairment of learning ability in sepsis.

[A study on porins of Escherichia coli HX88108]

To investigate the relationship between porins deficiency and the resistance of Escherichia coli HX88108. The porins of Escherichia coli HX88108 were studied by SDS-PAGE and were compared with the porins of standard strains. The result showed that E. coli HX88108 did not lose OmpF and OmpC, and the molecular weights of these two porins were 38 kd and 37 kd respectively. There is no relationship between the resistance of Escherichia coli HX88108 and porins deficiency.

Nitric oxide production in the CA1 field of the gerbil hippocampus after transient forebrain ischemia : effects of 7-nitroindazole and NG-nitro-L-arginine methyl ester

BACKGROUND AND PURPOSE

The present study was designed to examine the time course of nitric oxide (NO) production and the source of NO in the CA1 field of the gerbil hippocampus after transient forebrain ischemia.

METHODS

The production of NO in the CA1 field of the hippocampus after transient ischemia was monitored consecutively by measuring total NO metabolites (NOx-, NO2- plus NO3-) with the use of brain microdialysis. 7-Nitroindazole (7-NI) and NG-nitro-L-arginine methyl ester were used to dissect the relative contributions of neuronal NO synthase and endothelial NO synthase to the NO production. The histological outcomes of 7-NI in 5- and 10-minute global ischemia were also evaluated.

RESULTS

The production of NO in the CA1 field of the hippocampus after ischemia was dependent on the severity of ischemia. Ischemia for 2 or 5 minutes did not induce a significant increase in NOx- levels in the CA1 field of the hippocampus after reperfusion, whereas the 10- and 15-minute ischemias produced significant and persistent increases in NOx- levels. 7-NI did not inhibit the basal NOx- levels and showed no effects on NOx- levels after 5 minutes of ischemia. However, it completely inhibited the increased NOx- levels after 10 or 15 minutes of ischemia. 7-NI provided minor neuroprotection in 5 minutes but not in 10 minutes of global ischemia.

CONCLUSIONS

The increased NO level in the CA1 field of the hippocampus after ischemia is produced mostly by neuronal NO synthase, whereas the basal NO level mainly originates from endothelial NO synthase. The observed neuroprotective effect of 7-NI in 5-minute global ischemia in gerbils may not be due to neuronal NO synthase inhibition by this drug.

Mechanism of reduced flavin transfer from Vibrio harveyi NADPH-FMN oxidoreductase to luciferase

The mechanisms of reduced flavin transfer in biological systems are poorly understood at the present. The Vibrio harveyi NADPH-FMN oxidoreductase (FRP) and the luciferase pair were chosen as a model for the delineation of the reduced flavin transfer mechanism. FRP, which uses FMN as a cofactor to mediate the reduction of the flavin substrate by NADPH, exhibited a ping-pong kinetic pattern with a Km, FMN of 8 microM and a Km,NADPH of 20 microM in a single-enzyme spectrophotometric assay monitoring the NADPH oxidation. However, the kinetic mechanism of FRP was changed to a sequential pattern with a Km,FMN of 0.3 microM and a Km,NADPH of 0.02 microM in a luciferase-coupled assay measuring light emission. In contrast, the Photobacterium fischeri NAD(P)H-FMN oxidoreductase FRG showed the same ping-pong mechanism in both the single-enzyme spectrophotometric and the luciferase-coupled assays. Moreover, for the FRP, FMN at concentrations over 2 microM significantly inhibited the coupled reaction in both light intensity and quantum yield, and showed apparent noncompetitive and competitive inhibition patterns against NADPH and luciferase, respectively. No inhibition of the NADPH oxidation was detected under identical conditions. These results are consistent with a scheme that the reduced flavin cofactor of FRP is preferentially utilized by luciferase for light emission, the reduced flavin product generated by the reductase is primarily channeled into a dark oxidation, and luciferase competes against flavin substrate in reacting with the FRP reduced flavin cofactor. An FRP derivative containing 2-thioFMN as the cofactor was also used to further examine the mechanism of flavin transfer. Results again indicate a preferential utilization of the reductase reduced flavin cofactor by luciferase for the bioluminescence reaction.

Mechanism of reduced flavin transfer from Vibrio harveyi NADPH-FMN oxidoreductase to luciferase

The mechanisms of reduced flavin transfer in biological systems are poorly understood at the present. The Vibrio harveyi NADPH-FMN oxidoreductase (FRP) and the luciferase pair were chosen as a model for the delineation of the reduced flavin transfer mechanism. FRP, which uses FMN as a cofactor to mediate the reduction of the flavin substrate by NADPH, exhibited a ping-pong kinetic pattern with a Km, FMN of 8 microM and a Km,NADPH of 20 microM in a single-enzyme spectrophotometric assay monitoring the NADPH oxidation. However, the kinetic mechanism of FRP was changed to a sequential pattern with a Km,FMN of 0.3 microM and a Km,NADPH of 0.02 microM in a luciferase-coupled assay measuring light emission. In contrast, the Photobacterium fischeri NAD(P)H-FMN oxidoreductase FRG showed the same ping-pong mechanism in both the single-enzyme spectrophotometric and the luciferase-coupled assays. Moreover, for the FRP, FMN at concentrations over 2 microM significantly inhibited the coupled reaction in both light intensity and quantum yield, and showed apparent noncompetitive and competitive inhibition patterns against NADPH and luciferase, respectively. No inhibition of the NADPH oxidation was detected under identical conditions. These results are consistent with a scheme that the reduced flavin cofactor of FRP is preferentially utilized by luciferase for light emission, the reduced flavin product generated by the reductase is primarily channeled into a dark oxidation, and luciferase competes against flavin substrate in reacting with the FRP reduced flavin cofactor. An FRP derivative containing 2-thioFMN as the cofactor was also used to further examine the mechanism of flavin transfer. Results again indicate a preferential utilization of the reductase reduced flavin cofactor by luciferase for the bioluminescence reaction.

Measurement of the extracellular H2O2 in the brain by microdialysis

This paper reports on the protocol for the determination of H2O2 in the brain using in vivo microdialysis coupled with fluorometry of dichlorofluorescin oxidation. We applied this protocol to monitor changes in the concentration of H2O2 in the brain, in vivo, during ischemia and reperfusion. Using this method, changes in the level of H2O2 in the brain during ischemia and reperfusion were effectively determined. The present protocol provides a novel tool to study the production of reactive oxygen species in the brain.

The effect of dopamine depletion on the H2O2 production in the rat striatum following transient middle cerebral artery occlusion

The changes in the extracellular concentrations of rat striatal H2O2, dopamine (DA) and its metabolites during middle cerebral artery (MCA) occlusion and reperfusion were simultaneously examined by microdialysis, and the relationship between the ischemia-induced release of DA and the generation of H2O2 was estimated by assessing the effect of the lesion of the substantia nigra (SN). In the rats without SN lesions, a significant increase in the striatal H2O2 level was observed during the ischemia and reperfusion phases. In the rats with SN lesions, the ischemia-induced H2O2 production was not attenuated. These results suggest that DA is not an important source of H2O2 in cerebral ischemia and reperfusion.

8[prime]-Methylene Abscisic Acid (An Effective and Persistent Analog of Abscisic Acid)

We report here the synthesis and biological activity of a new persistent abscisic acid (ABA) analog, 8[prime]-methylene ABA. This ABA analog has one additional carbon atom attached through a double bond to the 8[prime]-carbon of the ABA molecule. (+)-8[prime]-Methylene ABA is more active than the natural hormone (+)-ABA in inhibiting germination of cress seed and excised wheat embryos, in reducing growth of suspension-cultured corn cells, and in reducing transpiration in wheat seedlings. The (+)-8[prime]-methylene analog is slightly weaker than (+)-ABA in increasing expression of ABA-inducible genes in transgenic tobacco, but is equally active in stimulating a transient elevation of the pH of the medium of corn cell cultures. In corn cells, both (+)-ABA and (+)-8[prime]-methylene ABA are oxidized at the 8[prime] position. ABA is oxidized to phaseic acid and (+)-8[prime]-methylene ABA is converted more slowly to two isomeric epoxides. The alteration in the ABA structure causes the analog to be metabolized more slowly than ABA, resulting in longer-lasting and more effective biological activity relative to ABA.

[Detection of p53 gene mutations in hepatocellular carcinoma]

This study screened 32 cases of hepatocellular carcinoma (HCC) from Chengdu detecting HBV DNA. HBsAg and p53 mutations by using Southern blot hybridization, immunohistochemistry and polymerase chain reaction/restriction enzyme digest methods, respectively. The results revealed all the cases had been infected by HBV; the frequency of HBV DNA integration into HCC cell was 72%, and the positive staining for HBsAg 96.3%(26/27). Of the 32 cases, 8 showed nuclear staining of p53 protein (25%), no mutation of p53 gene at all in 27 nontumorours liver tissues was identified. The resluts suggest the inactivation of p53 function may play a significant role in the genesis of HBV-associated HCC; however, the largely negative p53 mutation results in the current study conversely indicate that hepatocarcinogenesis may even involve other comprehensive mechanisms. Further studies are worth doing to evaluate the possible contribution of HBV to the p53 mutation in HCC.

The effect of hypothermia on H2O2 production during ischemia and reperfusion: a microdialysis study in the gerbil hippocampus

The changes in the extracellular concentration of hydrogen peroxide (H2O2) in gerbil hippocampus during ischemia and reperfusion were investigated by microdialysis coupled with fluorometry of dichlorofluorescin oxidation. In a normothermic condition (37.5 degrees C), a transient forebrain ischemia for 5 or 10 min produced a significant increase in hippocampal H2O2 immediately after the start of ischemia. The duration of this elevation after reperfusion was significantly shorter in gerbils subjected to 5 min of ischemia than in those subjected to 10 min of ischemia. Hypothermia at both 34 degrees C and 30 degrees C inhibited the increase in the H2O2 concentration during ischemia and reperfusion in gerbils subjected to 5 min of ischemia. In gerbils subjected to 10 min of ischemia, hypothermia delayed the onset of the increase in the H2O2 concentration and shortened the duration of the elevated H2O2 concentration. Hypothermia improved the histological outcome in the hippocampal CA1 neurons 7 days after ischemia. These findings suggest that the suppression of H2O2 production in ischemia and reperfusion is a possible mechanism of brain protection by hypothermia.

Vibrio harveyi NADPH:FMN oxidoreductase: preparation and characterization of the apoenzyme and monomer-dimer equilibrium

A rapid chromatography method was developed for the preparation of apoenzyme of Vibrio harveyi NADPH:FMN oxidoreductase with > or =80% yields. The apoenzyme bound one FMN per enzyme monomer with a dissociation constant of 0.2 microM at 23 degrees C. The reconstituted holoenzyme was catalytically as active as the native enzyme. FMN binding resulted in 87 and 92% of quenching of protein and flavin fluorescence, respectively, indicating a conformational difference between the apoprotein and the holoenzyme. Neither riboflavin nor FAD showed any appreciable binding to the cofactor site of the apoenzyme but both flavins were active substrates for the FMN-containing holoenzyme. 2-ThioFMN bound to the cofactor site of the apoenzyme with an affinity similar to that for FMN binding. The holoenzyme reconstituted with 2-thioFMN showed a 509-nm absorption peak, which represents a 19-nm red shift from the corresponding peak of the free flavin, and was catalytically active in using either FMN or 2-thioFMN as a substrate. The holoenzyme showed a concentration dependence in molecular sieve chromatography corresponding to higher apparent molecular weights at higher concentrations. Both the holoenzyme and the apoenzyme was shown at 4 degrees C by equilibrium ultracentrifugation to undergo dimerization with dissociation constants of 1.8 and 3.3 microM, respectively.

Flavin reductase P: structure of a dimeric enzyme that reduces flavin

We report the structure of an NADPH:FMN oxidoreductase (flavin reductase P) that is involved in bioluminescence by providing reduced FMN to luciferase. The 1.8 A crystal structure of flavin reductase P from Vibrio harveyi was solved by multiple isomorphous replacement and reveals that the enzyme is a unique dimer of interlocking subunits, with 9352 A2 of surface area buried in the dimer interface. Each subunit comprises two domains. The first domain consists of a four-stranded antiparallel beta-sheet flanked by helices on either side. The second domain reaches out from one subunit and embraces the other subunit and is responsible for interlocking the two subunits. Our structure explains why flavin reductase P is specific for FMN as cofactor. FMN is recognized and tightly bound by a network of 16 hydrogen bonds, while steric considerations prevent the binding of FAD. A flexible loop containing a Lys and an Arg could account for the NADPH specificity. The structure reveals information about several aspects of the catalytic mechanism. For example, we show that the first step in catalysis, which is hydride transfer from C4 of NADPH to cofactor FMN, involves addition to the re face of the FMN, probably at the N5 position. The limited accessibility of the FMN binding pocket and the extensive FMN-protein hydrogen bond network are consistent with the observed ping-pong bisubstrate--biproduct reaction kinetics. Finally, we propose a model for how flavin reductase P might shuttle electrons between NADPH and luciferase.

Gene overexpression, purification, and identification of a desulfurization enzyme from Rhodococcus sp. strain IGTS8 as a sulfide/sulfoxide monooxygenase

The oxidation of dibenzothiophene to dibenzothiophene sulfone has been linked to the enzyme encoded by the sox/dszC gene from Rhodococcus sp. strain IGTS8 (S. A. Denome, C. Oldfield, L. J. Nash, and K. D. Young, J. Bacteriol. 176:6707-6717, 1994; C. S. Piddington, B. R. Kovacevich, and J. Rambosek, Appl. Environ. Microbiol. 61:468-475, 1995). However, this enzyme has not been characterized, and the type of its catalytic activity remains unclassified. In this work, the sox/dszC gene was overexpressed in Escherichia coli, a procedure for the purification of the expressed enzyme was developed, and the properties of and the reactions catalyzed by the purified enzyme were characterized. This enzyme binds one flavin mononucleotide (Kd, 7 micrometers) or reduced flavin mononucleotide (FMNH2) (Kd < 10(-8) M) per 90,200-Da homodimer, and FMNH2 is an essential cosubstrate for its activity. Patterns of product formation were examined under different FMNH2 availabilities, and results indicate that this enzyme catalyzes a stepwise conversion of dibenzothiophene to the corresponding sulfoxide and subsequently to the sulfone. On the basis of isotope labeling patterns with H2(18)O and 18O2, dibenzothiophene sulfoxide and sulfone obtained their oxygen atom(s) from molecular oxygen rather than water in their formation from dibenzothiophene. The enzyme also utilizes benzyl sulfide and benzyl sulfoxide as substrates. Hence, it is identified as a sulfide/sulfoxide monooxygenase. This monooxygenase is similar to the microsomal flavin-containing monooxygenase but is unique among microbial flavomonooxygenases in its ability to catalyze two consecutive monooxygenation reactions.

NADPH diaphorase activity in mammalian retinas is modulated by the state of visual adaptation

NADPH diaphorase histochemistry is commonly used to identify cells containing nitric oxide synthase (NOS), the enzyme catalyzing the production of nitric oxide from L-arginine. NADPH diaphorase activity and NOS immunostaining was demonstrated in different cells of the vertebrate retina; photoreceptors, horizontal cells, amacrine cells, ganglion cells, and Müller cells. However, the physiological role of nitric oxide (NO) in the retina has yet to be elucidated. In this study, we tested the assumption that NADPH diaphorase activity in the retinas of rabbits and rats depended on the state of visual adaptation. In the rabbit, light adaptation enhanced NADPH diaphorase activity in amacrine cells and practically eliminated it in horizontal cells. Dark adaptation induced the opposite effects; the NADPH diaphorase activity was reduced in amacrine cells and enhanced in horizontal cells. Retinas from eyes that were injected intravitreally with L-glutamate exhibited a pattern of NADPH diaphorase activity that was similar to that seen in dark-adapted retinas. In rats, the NADPH diaphorase activity of amacrine and horizontal cells exhibited adaptation dependency similar to that of the rabbit retina. But, the most pronounced effect of dark adaptation in the rat's retina was an enhancement of NADPH diaphorase activity in Müller cells, especially of the endfoot region. Assuming that NADPH diaphorase activity is a marker for NOS, these findings suggest that NO production in the mammalian retina is modulated by the level of ambient illumination and support the notion that NO plays a physiological role in the retina.

Cloning, direct expression, and purification of a snake venom cardiotoxin in Escherichia coli

The cardiotoxin analogue III (CTX III), isolated from the Taiwan cobra (Naja naja atra) venom, is a sixty-amino acid, all beta-sheet protein. We report the direct expression of CTX III from its synthetic gene as inclusion bodies in Escherichia coli. The yield of the expressed protein is about 40 mg/liter of the culture. CTX III trapped as inclusion bodies is dissolved and refolded by the slow refolding technique. The refolded protein is purified by reverse phase high performance liquid chromatography. The purified and refolded CTX III sample is further characterized by SDS-PAGE, circular dichroism, two-dimensional NMR spectroscopy and haemolytic activity. To our knowledge, this is the first report of the direct expression and purification of snake venom cardiotoxins.

Ocular pigmentation protects the rabbit retina from gentamicin-induced toxicity

PURPOSE

This study was designed to investigate the possibility that gentamicin-induced retinal toxicity is dependent on ocular pigmentation by comparing the effects of the drug on the functional and morphologic integrity of the retina in albino and pigmented rabbits.

METHODS

In each rabbit, a solution of gentamicin sulfate was injected into the vitreous of one eye, and saline was injected into the other eye. Retinal function was assessed by electroretinogram (ERG) at different time intervals after injection. Retinal structure was examined at the light microscopic level.

RESULTS

In albino and pigmented rabbits, functional retinal damage developed to a maximal level within the first week after gentamicin injection. Thereafter, gradual recovery could be seen in eyes that suffered less than 80% maximal reduction in the ERG b-wave. For each dose >0.1 mg studied, retinal damage was more severe in the albino rabbits than in the pigmented ones. The degree of damage was not affected by the level of ambient illumination, nor was it reduced by the administration of N-acetylcystein, a free radical scavenger, together with gentamicin.

CONCLUSIONS

Ocular pigmentation partially protects the rabbit retina from the toxic action of gentamicin. This protection probably reflects binding of the drug by the melanin, which thereby reduces the concentration of the free gentamicin. When the initial gentamicin-induced retinal damage is expressed in < 80% reduction in the ERG, substantial recovery may occur in both strains of rabbits.

Crystallization and preliminary crystallographic analysis of NADPH:FMN oxidoreductase from Vibrio harveyi

Crystals of NADPH:FMN oxidoreductase from Vibrio harveyi have been obtained and characterized by X-ray diffraction. This enzyme plays a role in the generation of light in luminescent bacteria by providing reduced FMN to luciferase. Large, high quality crystals were grown using polyethylene glycol 6000 at pH 7.0. They crystallize in the monoclinic space group P2(1) with cell dimensions a = 51.2 A, b = 85.9 A, c = 58.1 A, beta = 109.3 degrees, and diffract to 1.8 A. We expect two molecules per asymmetric unit. High resolution data sets have been recorded and a search is under way for heavy-atom derivatives.

Vibrio harveyi NADPH-flavin oxidoreductase: cloning, sequencing and overexpression of the gene and purification and characterization of the cloned enzyme

NAD(P)H-flavin oxidoreductases (flavin reductases) from luminous bacteria catalyze the reduction of flavin by NAD(P)H and are believed to provide the reduced form of flavin mononucleotide (FMN) for luciferase in the bioluminescence reaction. By using an oligonucleotide probe based on the partial N-terminal amino acid sequence of the Vibrio harveyi NADPH-FMN oxidoreductase (flavin reductase P), a recombinant plasmid, pFRP1, was obtained which contained the frp gene encoding this enzyme. The DNA sequence of the frp gene was determined; the deduced amino acid sequence for flavin reductase P consists of 240 amino acid residues with a molecular weight of 26,312. The frp gene was overexpressed, apparently through induction, in Escherichia coli JM109 cells harboring pFRP1. The cloned flavin reductase P was purified to homogeneity by following a new and simple procedure involving FMN-agarose chromatography as a key step. The same chromatography material was also highly effective in concentrating diluted flavin reductase P. The purified enzyme is a monomer and is unusual in having a tightly bound FMN cofactor. Distinct from the free FMN, the bound FMN cofactor showed a diminished A375 peak and a slightly increased 8-nm red-shifted A453 peak and was completely or nearly nonfluorescent. The Kms for FMN and NADPH and the turnover number of this flavin reductase were determined. In comparison with other flavin reductases and homologous proteins, this flavin reductase P shows a number of distinct features with respect to primary sequence, redox center, and/or kinetic mechanism.

Mechanism of aldehyde inhibition of Vibrio harveyi luciferase. Identification of two aldehyde sites and relationship between aldehyde and flavin binding

Vibrio harveyi luciferase is sensitive to aldehyde substrate inhibition, and two kinetic schemes have been previously postulated to account for such an inhibition. One scheme depicts a sequential binding of 2 aldehyde molecules, yielding an active enzyme-aldehyde binary complex and subsequently an inactive enzyme-(aldehyde)2 ternary complex (Holzman, T. F., and Baldwin, T. O. (1983) Biochemistry 22, 2838-2846). This two-aldehyde model was later withdrawn, and recently, a different scheme was proposed, following which the prior binding of one aldehyde to the native luciferase forms an inactive dead-end complex (Abu-Soud, H. M., Clark, A. C., Francisco, W. A., Baldwin, T. O., and Raushel, F. M. (1993) J. Biol. Chem. 268, 7699-7706). In this work, kinetic and equilibrium studies were carried out to elucidate further the mechanism of aldehyde inhibition. Two, presumably independent, aldehyde-binding sites were detected, with a higher affinity site for the aldehyde substrate and a weaker affinity site for the aldehyde inhibitor. Binding to and dissociation from the inhibitor site by decanal were revealed by chemical relaxation analysis to be slow processes. Furthermore, whereas the binding of the decanal substrate enhances the affinity of the reduced riboflavin 5'-phosphate (FMNH2) site, the binding of decanal to the inhibitor site competes against FMNH2 binding, thus resulting in inhibition of luciferase activity. These findings are not compatible with either of the two earlier schemes mentioned above. A new kinetic model is formulated for the mechanism of aldehyde inhibition. Theoretical kinetic behaviors predicted on the basis of this model are in excellent agreement with experimental observations. A particularly reactive cysteine (residue 106) on the alpha subunit has been previously demonstrated to be at or near an aldehyde site (Fried, A., and Tu, S.-C. (1984) J. Biol. Chem. 259, 10754-10759). Evidence is presented to indicate that this residue is at or near the aldehyde inhibitor site. Relative locations of this residue and binding sites for FMNH2, the aldehyde substrate, and the aldehyde inhibitor are proposed.

Effect of moderate hypothermia on lipid peroxidation in canine brain tissue after cardiac arrest and resuscitation

BACKGROUND AND PURPOSE

We sought to examine the effect of moderate hypothermia (30 degrees C to 32 degrees C) initiated after resuscitation on the scavenging systems of free radicals and lipid peroxidation in canine brain tissue after cardiac arrest and resuscitation.

METHODS

Twenty-one dogs were divided into four groups: group A, nonischemic controls (shams) (n = 4); group B, 15-minute cardiac arrest without reperfusion (n = 4); group C, 15-minute cardiac arrest and standard resuscitation (n = 6); and group D, 15-minute cardiac arrest and hypothermic resuscitation (n = 7). During the period of 10 to 120 minutes after resuscitation, brain temperature and core temperature in group D remained at 30 degrees C to 32 degrees C and were 4 degrees C to 5 degrees C lower than in group C. For each dog, a sample of right parietal cerebral cortex was obtained from group A, group B, or from group C and group D at 2 hours after resuscitation. The sample was assayed for tissue malondialdehyde (MDA), the content of reduced glutathione (GSH), and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX).

RESULTS

In group B, a 15-minute cardiac arrest induced an increase in MDA, a significant reduction of GSH, and no change in SOD and GSH-PX activities compared with group A. In group C, there were further increases in MDA and reductions in GSH content and GSH-PX activity compared with group A; SOD activity remained substantially unchanged. The content of MDA was higher in group D than in group A but less elevated in group D than in group C. The GSH content and SOD and GSH-PX activities were significantly higher in group D than in group C.

CONCLUSIONS

Moderate hypothermia initiated after resuscitation can significantly inhibit the accumulation of lipid peroxidation products and the consumption of free radical scavengers in the brain tissue.

[Production and characterization of anti-human hepatocellular carcinoma monoclonal antibodies]

The hepatocellular carcinoma (HCC) cell line, QGY-7703, derived from a Chinese patient, was used to immunize the BALB/c mice. Fifteen hybridomas producing McAb that reacted with QGY-7703 cells were isolated from 858 hybridomas created in three cell fusions. In further studies two McAb, namely, AQGY1 and A-QGY2, were selected which specifically stained HCC cells grown in vitro. The reactivity of these McAb was not removed by the absorption by homogenates of the normal liver, but was by homogenates of HCC cells. A-QGY1 and A-QGY2 also reacted definitely with HCC cells in liver tissues of HCC patients, but neither with other cells in the tissues nor with nontransformed liver tissues of the same patients. Furthermore these two McAb stained the adult or fetal liver tissues, nor all of the other normal or tumor tissues that had been tested. Blocking and absorbing experiments revealed that A-QGY1 and AQGY2 antigens had no immunohomogenicity with antigens such as HBsAg, HBcAg, HBeAg, AFP and CEA. The specificity of these two McAb may be used potentially for the sero diagnosis, histologic identification, radioimmunoimaging and destruction of human hepatocellular carcinoma.

[Primary serologic investigation of HBV-like virus existence in domestic animals and fowls]

Using the reagent kits for detecting human HBV, primary serologic investigation was made in 6 kinds of domestic animals and fowls (total 673) by ELISA, spot hybridization and immuno-electronmicroscopy. The results showed that some sera samples of pigs, rabbits, chicken and geese were HBsAg, HBeAg positive and positive for spot hybridization by using 3(2)P-HBV-DNA probe, which suggested that HBV-like viruses might exist in those domestic animals and fowls. HBV-like virus particles were seen in one pig serum sample which was HBsAg positive. The particles could be divided into three forms in shape, large spherical particle (40-55nm), small spherical particle (20-30nm) and short filament particle. The further studies are needed.