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H Karoui

Publications and source records attributed to H Karoui.

At least 37 records · Page 2Linked to original sources
PubMed1996

A new scorpion venom toxin paralytic to insects that affects Na+ channel activation. Purification, structure, antigenicity and mode of action.

A new toxin, BotIT2, with a unique mode of action on the isolated giant axon of the cockroach Periplaneta americana and DUM (dorsal unpaired median) neurons, has been purified from the venom of the scorpion Buthus occitanus tunetanus. Its structural, antigenic and pharmacological properties are compared to those of three other groups of neurotoxins found in Buthidae scorpion venoms. Like excitatory, depressant and alpha-type insect-selective neurotoxins, BotIT2 is toxic to insects, but shows the following common and distinctive characteristics. (a) As alpha-type toxins, BotIT2 lack strict selectivity to insects; they have measurable but low toxicity to mice. (b) As depressant toxins and unlike alpha-type toxins, BotIT2 is able to displace iodinated AaHIT from its binding sites in insect neuronal membranes. This indicates that the binding site for BotIT2 is identical, contiguous or in allosteric interaction with that of AaHIT and depressant toxins. (c) The BotIT2 amino acid sequence shows strong similarity to depressant toxins. However, unexpectedly, despite this high sequence similarity, BotIT2 shares moderate cross-antigenic reactivity with depressant toxins. (d) Voltage and current-clamp studies show that BotIT2 induces limited depolarization concomitantly with the development of depolarizing after potential, repetitive activity and later plateau potentials terminated by bursts. Under voltage-clamp conditions, BotIT2 specifically acts on Na+ channels by decreasing the peak Na+ current and by simultaneously inducing a new current with very slow activation/deactivation kinetics. The voltage dependence of this slow current is not significantly different from that of the control current. These observations indicate that BotIT2 chiefly modifies the kinetics of axonal and DUM neuronal membrane Na(+)-channel activation.

Amino Acid Sequence↗
PubMed1996

Detection of thiyl radical adducts formed during hydroxyl radical- and peroxynitrite-mediated oxidation of thiols--a high resolution ESR spin-trapping study at Q-band (35 GHz).

Thiyl radicals (RS.) formed during peroxynitrite- or hydroxyl radical-dependent oxidation of thiols, i.e., glutathione (GSH) and L-cysteine (CySH) were trapped with 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) and analyzed by X-band and Q-band electron spin resonance (ESR) spectroscopy. At X-band, the ESR parameters of DMPO-glutathionyl radical adduct (DMPO/.SG) and DMPO-hydroxyl radical adduct (DMPO/.OH) are nearly similar in aqueous solutions and as a result, except for the lowfield spectral line, the remaining spectral lines of DMPO/ .SG virtually over-lap with those of the DMPO/.OH adduct. In contrast, at Q-band, most of the spectral lines due to the DMPO/.SG were separated from the DMPO/ .OH. Inclusion of a superoxide dismutase (SOD) mimic completely abolished the formation of the DMPO/.OH adduct and not the DMPO/.SG adduct during ONOO(-)-mediated oxidation of GSH and DMPO. In the presence of formate, the DMPO/.SG spectrum was replaced by the DMPO/.CO2- spectrum which was monitored by Q-band ESR spectroscopy. Thus, spin-trapping at Q-band provides unambiguous proof for the glutathionyl radical-dependent oxidation of formate by peroxynitrite. High resolution Q-band ESR spectra of DMPO/.Scys were also obtained. Biological applications of the Q-band spin-trapping technique to detect thiyl radicals in cellular systems are discussed.

Biological Assay↗
PubMed1996

A recombinant insect-specific alpha-toxin of Buthus occitanus tunetanus scorpion confers protection against homologous mammal toxins.

We have constructed a cDNA library from venom glands of the scorpion Buthus occitanus tunetanus and cloned a DNA sequence that encodes an alpha-toxin. This clone was efficiently expressed in Escherichia coli as a fusion protein with two Ig-binding (Z) domains of protein A from Staphylococcus aureus. After CNBr treatment of the fusion protein and HPLC purification, we obtained approximately 1 mg recombinant apha-toxin/l bacterial culture. The toxin, called Bot XIV, displays no toxicity towards mammals but is active towards insects as shown by its paralytic activity against Blatella germanica cockroach and by electrophysiological studies on Periplaneta americana cockroaches. The Bot XIV protein fused to two Z domains is highly immunogenic in mice and induces production of antisera that specifically recognize and neutralize highly toxic components that had been injected into mice. This fusion protein could be very useful for development of potent protective antisera against scorpion venoms.

Amino Acid Sequence↗
PubMed1996

Effect of superoxide dismutase mimics on radical adduct formation during the reaction between peroxynitrite and thiols--an ESR-spin trapping study.

We have reexamined the formation and reactions of radicals formed from peroxynitrite (ONOO-)-mediated oxidation of glutathione (GSH), L-cysteine (Cys), N-acetyl-D,L-penicillamine (NAP), and sodium bisulfite (NaHSO3). Sulfur-centered and superoxide union radicals were trapped using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and the radical adducts were analyzed by electron spin resonance (ESR) spectroscopy. The following sulfur-centered radicals were detected: glutathionyl radical (GS') from GSH, L-cysteinyl radical ('Scys) from L-cysteine, N-acetyl-D,L-penicillamine thiyl radical ('SNAP) from NAP, and sulfite anion radical (SO3-.) from NaHSO3. Additionally the formation of the hydroxyl radical adduct of DMPO (DMPO/'OH) was observed. DMPO/'OH formation was totally inhibited by low-molecular-weight superoxide dismutase (SOD) mimics. This suggests that DMPO/'OH was formed from the decay of the superoxide radical adduct of DMPO. In the presence of SOD mimics, the DMPO-sulfur-centered adducts were more persistent, suggesting that O2-. is partially responsible for the instability of DMPO-thiyl adducts. Sulfur-centered radicals formed during oxidation of thiols and sulfite by peroxynitrite react with ammonium formate to form the carbon dioxide anion radical (CO2-.). We conclude that sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite arise from a hydroxyl-radical-independent mechanism. Biological implications of peroxynitrite-mediated oxidation of thiols as well as the use of SOD mimics in biological spin-trapping are discussed.

Cyclic N-Oxides↗
PubMed1996

Characterization of sulfur-centered radical intermediates formed during the oxidation of thiols and sulfite by peroxynitrite. ESR-spin trapping and oxygen uptake studies.

Using a novel phosphorylated spin trap, 5-diethoxy-phosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), an analog of the commonly used trap 5,5'-dimethyl-1-pyrroline N-oxide (DMPO), we have investigated the reactions of sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite. The predominant species trapped in all cases are the corresponding sulfur-centered radicals, i.e. glutathionyl radical (GS) from glutathione (GSH), N-acetyl-DL-penicillamine thiyl radical (S-NAP) from N-acetyl-DL-penicillamine (NAP) and sulfate anion radical (SO3-) from sulfite. These radicals consume molecular oxygen forming either peroxyl or superoxide anion radicals. GS, S-NAP, and (SO3-)-derived radicals react with ammonium formate to form the carbon dioxide anion radical (CO2-). Further support of spin adduct assignments and radical reactions are obtained from photolysis of S-nitrosoglutathione and S-nitroso-N-acetyl-DL-penicillamine. We conclude that the direct reaction of peroxynitrite with thiols and sulfate forms thiyl and sulfate anion radicals, respectively, by a hydroxyl radical-independent mechanism. Pathological implications of thiyl radical formation and subsequent oxyradical-mediated chain reactions are discussed. Oxygen activation by thiyl radicals formed during peroxynitrite-mediated oxidation of glutathione may limit the effectiveness of GSH against peroxynitrite-mediated toxicity in cellular systems.

Cyclic N-Oxides↗
PubMed1995

Cerastocytin, a new thrombin-like platelet activator from the venom of the Tunisian viper Cerastes cerastes.

Cerastocytin, a thrombin-like enzyme from the venom of the desert viper, Cerastes cerastes, has been purified to homogeneity by fast performance liquid chromatography (FPLC) on Mono-Q and Mono-S columns. It is a basic protein (isoelectric point higher than 9) made of a single polypeptide chain of 38 kDa. Its N-terminal polypeptide sequence shows strong similarities with other thrombin-like enzymes from snake venoms. Nanomolar concentrations of cerastocytin induce aggregation of blood platelets. This activity is inhibited by chlorpromazine, theophylline and mepacrine, as in the case of platelet aggregation stimulated by low doses of thrombin. Cerastocytin also possesses an amidolytic activity measured with the thrombin chromogenic substrate S-2238. The platelet aggregating activity and the amidolytic activity of cerastocytin were inhibited by PMSF, TPCK, TLCK and soybean trypsin inhibitors, suggesting that cerastocytin is a serine proteinase. On the other hand, both amidolytic activity and platelet aggregating activity of cerastocytin were unaffected by hirudin or by antithrombin III in the presence of heparin. High concentrations of cerastocytin (1-10 microM) also cleaved prothrombin and Factor X.

Amino Acid Sequence↗
PubMed1995

5-(Diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide: a new efficient phosphorylated nitrone for the in vitro and in vivo spin trapping of oxygen-centered radicals.

5-(Diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO, 2), a new spin trap, has been synthesized via a two-step synthetic route, and its ability to spin trap oxy radicals in biological milieu has been addressed. The in vitro spin trapping of hydroxyl and superoxide radicals was investigated in a phosphate buffer 0.1 M, and the hyperfine coupling constants of the spin adducts were determined. The rates of spin trapping of hydroxyl and superoxide radicals with 2 were found to be close to those reported for 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, the DEPMPO-superoxide spin adduct was shown to be significantly more persistent (15 times at pH 7) than the DMPO--superoxide spin adduct. Using 2 as a spin trap, the production of superoxide has been clearly characterized during the reperfusion of ischemic isolated rat hearts.

Animals↗
PubMed1994

Purification from Vipera lebetina (desert adder) venom of a protein that depletes human complement.

A rapid and efficient procedure for purification from Vipera lebetina venom of a low molecular weight anticomplement protein is described. The procedure used gel filtration on Superose 12, followed by ion-exchange chromatography on a Mono Q column. The purified protein migrated on SDS-PAGE as a single band of about 25,000 Da under nonreducing conditions and as a band of 16,000 Da under reducing conditions. Its isoelectric point was estimated to be 7.6 +/- 0.1. The isolated Vipera lebetina protein was found to decrease the hemolytic activity in human serum measured by assays for classical pathway and alternative pathway activation. The loss of the complement activity could be ascribed, at least in part, to a proteolytic cleavage of the alpha chains of C3 and C4. This protein was also found to be without action on human blood coagulation and on purified fibrinogen and Factor B.

Blood Coagulation↗
PubMed1993

[Pica in tunisian children. Results of a survey performed in a polyclinic of the tunisian social security national administration].

During a 15 month-period, 63, 10 to 59 month-old children, with pica habits were collected in a day care centre of the Caisse nationale de sécurité sociale in Tunis. Anemia was the main alert sign. They were compared with 43 non pica children presenting with a similar degree of anemia. The male to female ratio was 1.42. A family history of pica was present in 57% of the cases. Most children ingested earth but 50% of the patients ingested multiple substances. The beginning of the eating disorder was observed between 12 and 18 months in 71% of the cases. 95% of pica patients were from low income parents and urban status. No differences were observed between the pica children and the anemic children without pica habits in term of anamnestic, clinical and biological data. Treatment with iron supplements led to cessation of pica in most patients. The physiopathological hypothesis were dominated by iron and zinc deficiency of which geophagia can be, at the same time, the cause and the consequence. From our study, pica appears to remain very frequent among Tunisian children. Its prevention requires information of parents and dietary prevention of early iron deficiency.

Anemia, Hypochromic↗
PubMed1991

Purification and characterization of a fibrinogenase from Vipera lebetina (desert adder) venom.

A fibrinogenase from Vipera lebetina venom was isolated by gel filtration in a Superose 12 column prep grade HR 16/50 and by ion-exchange in a Mono Q HR 5/5 column. The purified enzyme, which was obtained with a yield of 8 mg from 60 mg of crude venom, is a glycoprotein having an isoelectric point of 5.9 +/- 0.1 and a mol. wt of 26,000 +/- 1000 as estimated by SDS-PAGE. The biochemical characterization of the enzyme revealed that it hydrolyzes readily the B beta chain of fibrinogen and the A alpha chain as well as fibrin and casein. Over a pH range from 4 to 11 the enzyme was not inactivated by a 20 min treatment at 90 degrees C. The isolated fibrinogenase is inhibited by ethylenediamine tetraacetic acid, dithiothreitol and L-cysteine but not by phenylmethylsulfonyl fluoride. On the other hand, it is activated by Ca2+ and Mg2+. Purified fibrinogenase up to a dose of 100 micrograms/mouse shows no toxicity and has no hemorrhagic activity.

Animals↗
PubMed1991

[Characteristics of the first penicillinase-producing strains of Neisseria gonorrhoeae isolated in Tunisia].

The first penicillinase-producing strain of Neisseria gonorrhoeae was recently isolated in Tunisia (1989). Betalactamase production was detected by the iodometric agar test. Minimal inhibitory concentrations (MICs) in agar medium were 128 micrograms/ml for penicillin, ampicillin and amoxycillin. With the amoxycillin-clavulanic acid combination, MIC fell to 0.25 microgram/ml. An Asian-type plasmid pattern was evidenced in this strain, with presence of the 2.6 Mdal cryptic plasmid and of a 4.5 Mdal plasmid.

Adult↗
PubMed1986

Histidine-rich domain of the knob protein of the human malaria parasite Plasmodium falciparum.

Membranes of erythrocytes infected with the human malaria parasite Plasmodium falciparum develop protrusions called knobs. These structures are essential for the survival of the parasite in the host, and their induction requires the synthesis of the knob protein by the parasite. We describe the isolation of a cDNA clone encoding the amino-terminal half of the knob protein. A cDNA library was constructed from RNA prepared from ring stages of a P. falciparum isolate that has retained its ability to induce knobs (knob+ phenotype). A synthetic oligonucleotide probe encoding polyhistidine was used to isolate the cDNA clone, which encodes the amino-terminal half of a polypeptide with all the known attributes of the knob protein. The gene is not transcribed in variants that do not synthesize the knob protein and thereby cannot induce knobs (knob- phenotype). The apparent lack of transcription in knob- variants is due to different mechanisms: although the gene is present in one knob- isolate, it has been deleted in a cloned knob- variant. The primary structure of the polypeptide deduced from a partial sequence of the cDNA is distinctly different from other malarial histidine-rich polypeptides. The amino-terminal sequence shows the characteristic features of a signal peptide. This is followed by a histidine-rich domain and a subsequent region which contains one histidine. Peptide map analysis of the knob protein is consistent with the structural features deduced from the sequence analysis of the cDNA.

Amino Acid Sequence↗
PubMed1984

[Bronchoscopy in the diagnosis of complicated pulmonary hydatid cyst in children].

The diagnosis of pulmonary hydatid cysts in children is generally easy and does not require endoscopic exploration, because the radiological aspects of an intact or a complicated cyst are most often suggestive. There are, nevertheless, some cases of pulmonary hydatids where the cyst is partially evacuated and then infected, whose radiological image is atypical showing parenchymatous opacities (systematised or not) which are readily associated with adenopathy. Usually immunology fails to aid the clinician in this later stage in the cyst's evolution. Two recent cases are reported of Tunisian children aged 5 and 10 years old with chronic pulmonary opacities posing a diagnostic problem. One child presented with a persistent cough, the other with recurrent haemoptysis and both had negative immunology. Bronchoscopy enabled a positive diagnosis to be made in both cases by showing the presence of an intra-bronchial membrane. A simultaneous bronchogram showed an arrest of the contrast in the affected bronchial segment. Although non specific, this image of arrested contrast should in our opinion be discussed in the differential diagnosis when the membrane could not be seen at bronchoscopy. At operation surgery confirmed the retention of infected membrane but in our two children infection had led to the destruction of a lower lobe which was removed. These situations where the diagnosis of pulmonary hydatids is difficult are far from being rare in countries of hgh endemiology such as Tunisia. Our observations show the advantage of bronchoscopy, which sometimes enable one to see or to remove a fragment of the membrane and thus entrust the child to a surgeon with a definitive diagnosis.

Bronchoscopy↗
PubMed1983

Mini-F encoded proteins: identification of a new 10.5 kilodalton species.

The elements which ensure the maintenance of the F plasmid are located in its f5 EcoRI restriction fragment. This f5 fragment constitutes a mini-F plasmid showing the same stability and copy number control as the entire F plasmid. The proteins expressed in minicells by wild-type or mutated f5 fragments were analysed by pH gradient two-dimensional electrophoresis. We identified seven f5-encoded polypeptides and located their genes on the F map. Among them, H1, an acidic polypeptide of mol. wt. 10.5 K, had not been detected before. It is in fact the most abundant f5-encoded polypeptide identified so far. In addition, we showed that both 10.5-K and 12-K protein bands detected by SDS-polyacrylamide gel electrophoresis are, respectively, composed of two polypeptides, H1 and H2, G1 and G2, of different isoelectric points. Polypeptides H2 and G2, respectively, share common coding sequences with polypeptides H1 and G1. Their possible biological significance is discussed. The sequences coding for polypeptides H1/H2 and G1/G2 are clustered in a 800-bp long region located between the two mini-F origin sites and are proposed to be organized as an operon. The results reported in the accompanying paper point out the importance of polypeptides G1/G2 and H1/H2 in the relationship between the F plasmid and its host.

Bacterial Proteins↗
PubMed1983

Ham22, a mini-F mutation which is lethal to host cell and promotes recA-dependent induction of lambdoid prophage.

A mini-F region 800 bp long, located between the two F origin sites, plays an essential role in the relationship between the F plasmid and its host. This region comprises two sets of overlapping coding sequences: the first set codes for the newly identified H1 and H2 polypeptides; the second set codes for polypeptides G1 and G2. A mini-F amber mutation (Ham22) causes the virtual disappearance of polypeptides H1 and H2 but only slightly reduces synthesis of polypeptides G1 and G2. This mutation: (i) renders mini-F hybrids lethal to the host cells (conditional Hos- phenotype for host survival) and (ii) causes the induction of a resident prophage in recA+ strains (conditional Map- phenotype for maintenance of the prophage). When an additional mutation prevents the synthesis of polypeptides G1 and G2, both the lethal character and the induction of the prophage are abolished. We conclude: (i) that polypeptides G1 and/or G2 are specific mini-F polypeptides involved in the plasmid-mediated killing effect and in the recA-dependent induction of the resident prophage and (ii) that, in normal conditions, polypeptides H1 and/or H2 negatively control (directly or indirectly) the action of polypeptides G1 and/or G2. In relation to the analysis of indirect induction mediated by u.v.-irradiated lambda mini-F hybrids, we propose that polypeptides G1 and/or G2 are specific mini-F products involved in the activation of the bacterial SOS pathway. The H1/H2 and G1/G2 polypeptides could constitute the controlled mini-F signal enabling the coordination between cell division and F plasmid replication.

Bacteriophage lambda↗
PubMed1976

[Study of the threshold dose of penicillin which induces an epileptogenic focus during ontogenesis in the rabbit].

A local application on the cortex surface of a very small drop of Ringer solution containing Penicillin was performed to establish the threshold dose required to elicit and epileptogenic focus and consequently the occuring latency of it. Threshold doses are small (20 - 60 International Units) and show a significant decrease during the maturation of the C.N.S. On the other hand latencies, whatever the animal's age, decrease fairly. The results are confronted to the various supposed modes of action of penicillin, modes which involve a dysfonctioning of the Na+ and K+ ionic pump.

Age Factors↗
PubMed1975

[Effect of anoxia on the evoked somesthesic response during rabbit maturation].

The resistance to anoxy of the somesthetic evoked response (S.E.R.) has been studied on the young rabbit from birth to ten days. An obvious decrease of this resistance is being observed from the eighth day. The authors drew a parallel from their results and the well known modifications of the oxydative metabolism of the C.N.S. during maturation.

Age Factors↗