PubMed Health⌕ Search

Biomedical subjects

D Levanon

Publications and source records attributed to D Levanon.

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

Evidence for cytochrome P-450 and P-450-mediated benzo(a)pyrene hydroxylation in the white rot fungus Phanerochaete chrysosporium.

The presence of cytochrome P-450 and P-450-mediated benzo(a)pyrene hydroxylase activity in both microsomal and soluble fractions of the white rot fungus Phanerochaete chrysosporium was shown. The reduced carbon monoxide difference spectrum showed maxima at 448-450 and 452-454 nm for microsomal and cytosolic fractions, respectively. Both P-450 fractions produced a Type I substrate binding spectrum on addition of benzo(a)pyrene. Activity for benzo(a)pyrene hydroxylation was NADPH dependent and inhibited by carbon monoxide. Km values for activity showed a difference between the cellular fractions with a Km of 89 microM for microsomal P-450 and 400 microM for cytosolic P-450. The Vmax values observed were 0.83 nmol min-1 (nmol microsomal P-450)-1 and 0.4 nmol min-1 (nmol cytosolic P-450)-1. The results indicate that P-450-mediated benzo(a)pyrene hydroxylase activity could play a role in xenobiotic transformation by this fungus beside the known ligninolytic exocellular enzymes.

Basidiomycota↗
PubMed1996

A large variety of alternatively spliced and differentially expressed mRNAs are encoded by the human acute myeloid leukemia gene AML1.

The human chromosome 21 acute myeloid leukemia gene AML1 is frequently rearranged in the leukemia-associated translocations t(8;21) and t(3;21), generating fused proteins containing the amino-terminal part of AML1. In normal blood cells, five size classes (2-8 kb) of AML1 mRNAs have been previously observed. We isolated seven cDNAs corresponding to various AML1 mRNAs. Sequencing revealed that their size differences were mainly due to alternatively spliced 5' and 3' untranslated regions, some of which were vast, exceeding 1.5 kb (5') and 4.3 kb (3'). These untranslated regions contain sequences known to control mRNA translation and stability and seem to modulate AML1 mRNA stability. Further heterogeneity was found in the coding region due to the presence of alternatively spliced stop codon-containing exons. The latter led to production of polypeptides that were smaller than the full-length AML1 protein; they lacked the trans-activation domains but maintained DNA binding and heterodimerization ability. The size of these truncated products was similar to the AML1 segment in the fused t(8;21) and t(3;21) proteins. In thymus, only one mRNA species of 6 kb was detected. Using in situ hybridization, we showed that its expression was confined to the cortical region of the organ. The 6-kb mRNA was also prominent in cultured peripheral blood T cells, and its expression was markedly reduced upon mitogenic activation by phorbol myristate acetate (TPA) plus concanavalin A (ConA). These results and the presence of multiple coding regions flanked by long complex untranslated regions, suggest that AML1 expression is regulated at different levels by several control mechanisms generating the large variety of mRNAs and protein products.

Alternative Splicing↗
PubMed1996

Manganese-enhanced biotransformation of atrazine by the white rot fungus Pleurotus pulmonarius and its correlation with oxidation activity.

Manganese enhanced atrazine transformation by the fungus Pleurotus pulmonarius when added to a liquid culture medium at concentrations of up to 300 microM. Both N-dealkylated and propylhydroxylated metabolites accumulated in the culture medium, with the former accumulating to a greater extent than did the latter. Lipid peroxidation, oxygenase and peroxidase activities, and the cytochrome P-450 concentration increased. In addition, an increase in the spectral interactions between atrazine and components in the cell extract was observed. Antioxidants, mainly nordihydroguaiaretic acid, which inhibits lipoxygenase, peroxidase, and P-450 activities, and piperonyl butoxide, which inhibits P-450 activity, inhibited atrazine transformation by the mycelium. It is suggested that the stimulation of oxidative activity by Mn might be responsible for increasing the biotransformation of atrazine and for nonspecific transformations of other xenobiotic compounds.

Antioxidants↗
PubMed1996

Regenerating synovial lining of the normal rabbit knee: a scanning electron microscopy study.

Regeneration of the synovial lining in the synovectomized rabbit knee was studied using the scanning electron microscope. The resected synovia regenerated considerably 3 weeks after synovectomy. However, 44 weeks following excision, their surface morphology was still very different from that of the normal tissue of intact animals. The regenerated synovia were characterized by three main features: the large number of various patterns, the many fields harboring fibrillation and the almost total lack of a bubble layer (the latter was formerly shown to be predominant on normal, intact synovia). The surface morphology of the non-operated (contralateral) knee differed greatly from that of normal synovia. The surface of sham-operated synovia was totally covered by the bubble layer. The appearance of vast fields harboring fibrillations indicated deficient ultrastructural regeneration. The altered surface morphology of the contralateral synovia was a novel finding. We wonder whether it would be appropriate to propose that the systemic reaction induced by synovectomy of the experimental knee initiated the synovial appearances recorded on the contralateral knee. The data reported here rule out the possibility of using the contralateral leg as an intact control.

Animals↗
PubMed1995

Common promoter features in human and mouse liver type phosphofructokinase gene.

The liver-type phosphofructokinase is a key glycolytic enzyme encoded by genes residing on human and mouse chromosomes 21 and 10 respectively. Genomic DNA regions upstream of the initiator ATG spanning 2.6Kb and 3.4Kb of human and mouse liver-type phosphofructokinase gene were sequenced and analyzed. The proximal 0.4Kb region of both genes featured a CpG island containing 60%-73% GC residues. The first 120 nucleotides preceding the ATG are highly conserved displaying 73% of sequence similarity between human and mouse genes. While this region lacks TATA and CAAT boxes it contains four Sp1 binding sites and was capable of promoting a non regulated expression of the reporter gene chloramphenicol acetyl transferase, in transfection assays. Additional conserved elements were found further upstream at the 5'-region of both the human and mouse genes. They consisted of two Alu repeats and several sequence motifs known to serve as transcription factors binding sites.

Animals↗
PubMed1995

Quantitative analysis of chondroitin sulphate retention by tannic acid during preparation of specimens for electron microscopy.

The ability of tannic acid to enhance binding of glycosaminoglycans to purified collagen was analysed in an in vitro system using amino sugar analysis on an amino acid analyser, transmission electron microscopy, and scanning electron microscopy. Collagen was purified by digestion with trypsin, papain, and hyaluronidase. Purified collagen was incubated with hyaluronic acid or with chondroitin sulphate glycosaminoglycan and then treated with tannic acid. Tannic acid was found to enhance retention during preparation for electron microscopy of either of the glycosaminoglycans onto collagen fibres. The ability of tannic acid to enhance binding of collagen and glycosaminoglycans might explain, at least in part, its structural reinforcement effect on resected synovial joint-apposing surfaces during preparation for scanning electron microscopy.

Amino Sugars↗
PubMed1994

AML1, AML2, and AML3, the human members of the runt domain gene-family: cDNA structure, expression, and chromosomal localization.

cDNAs corresponding to three human runt domain containing genes, AML1, AML2, and AML3, were isolated and characterized. In addition to homology in the highly conserved runt domain, extensive sequence similarities were also observed in other parts of the proteins. All three carried an identical, putative ATP binding site -GRSGRGKS-, and their C-terminal halves were particularly rich in proline and serine residues. While AML1 cDNAs were cloned by others, AML2 represents a new member, not previously described, of the runt domain gene family, and AML3 was identified as the human homologue of mouse PEB-P2 alpha A. The chromosomal location of AML1 to chromosome 21q22 was confirmed, while AML2 and AML3 were mapped to chromosome regions 1p36 and 6p21, respectively. Analysis of AML1 and AML2 expression in hematopoietic cell lines revealed a distinct pattern of expression.

Amino Acid Sequence↗
PubMed1994

Overexpression of liver-type phosphofructokinase (PFKL) in transgenic-PFKL mice: implication for gene dosage in trisomy 21.

The human liver-type subunit of the key glycolytic enzyme, phosphofructokinase (PFKL), is encoded by a gene residing on chromosome 21. This chromosome, when triplicated, causes the phenotypic expression of Down's syndrome (trisomy 21). Increased phosphofructokinase activity, a result of gene dosage, is commonly found in erythrocytes and fibroblasts from Down's syndrome patients. We describe the construction of transgenic mice overexpressing PFKL for use as a well-defined model system, in which the effects of PFKL overexpression in various tissues, and throughout development, can be studied. Mice transgenic for a murine PFKL 'gene cDNA' hybrid construct were found to overexpress PFKL in a tissue-specific manner resembling that of the endogenous enzyme. Although unchanged in adult brain, PFK specific activity was found to have been almost doubled in brains of embryonic transgenic-PFKL mice, suggesting that the extra copies of the PFKL gene are expressed during the developmental period. This pattern of overexpression of PFKL in brains of transgenic-PFKL mice suggests that gene-dosage effects may be temporally separated from some of their consequences, adding an additional layer of complexity to the analysis of gene dosage in trisomy 21.

Aging↗
PubMed1993

Isolation and Characterization of a Novel Atrazine Metabolite Produced by the Fungus Pleurotus pulmonarius, 2-Chloro-4-Ethylamino-6-(1-Hydroxyisopropyl)Amino-1,3,5-Triazine.

The white rot fungus Pleurotus pulmonarius exhibited metabolism of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) in liquid culture, producing the dealkylated metabolites desethylatrazine, desisopropylatrazine, and desethyl-desisopropylatrazine. A fourth, unknown metabolite was also produced. It was isolated and was identified as 2-chloro-4-ethylamino-6-(1-hydroxyisopropyl)amino-1,3,5-triazine by gas chromatography-mass spectrometry, Fourier transformed infrared spectroscopy, and H nuclear magnetic resonance analysis. The structure of this metabolite was confirmed by chemical synthesis of the compound and comparison with the fungally produced metabolite.

Journal Article↗
PubMed1993

Evaluation of the use of tannic acid in preparation of the rabbit knee meniscus for scanning electron microscopy.

The femoral faces of medial and lateral menisci of the rabbit knee were structurally reinforced with tannic acid and studied using the scanning electron microscope. Significant improvement in preservation of the meniscal surfaces, as compared to previous studies, was brought about by the structural reinforcement technique. Menisci, although detacted from tibial plateaux, retained well their shape, dimensions, and microarchitecture. Differences in surface morphology between medial and lateral menisci and between longitudinal sectors on menisci were recorded. Appearances of surface irregulatities were reduced to a very low level, and the possibility that this minimum exists in situ is forwarded.

Animals↗
PubMed1992

Protection against tabun toxicity in mice by prophylaxis with an enzyme hydrolyzing organophosphate esters.

We demonstrate here the correlation between protection afforded by pretreatment alone with parathion hydrolase purified from Pseudomonas sp. against tabun toxicity in mice and the kinetic parameters which are assumed to determine the in vivo detoxification of tabun by the same enzyme. Results show that 15 and 22 micrograms of parathion hydrolase per animal conferred a protective ratio of 3.94 and 5.65 respectively, against tabun toxicity, without post-exposure treatment.

Animals↗
PubMed1992

The synovial lining of the rabbit knee: a scanning electron microscopy study of specimens reinforced structurally with tannic acid.

Medial and lateral synovial linings of the rabbit knee, structurally reinforced with tannic acid during fixation, were studied in the scanning electron microscope. Low-resolution micrographs revealed, in both linings, gross architecture of four types: accordion-like, lobe-like, fatty areolar, and flattened areas. In high resolution, both cellular and acellular surfaces were recorded. A novel, 'bubble-like' appearance, of unknown nature and origin, accounted for 70% of both linings. No definite correlation between anatomical location, gross type, or microarchitectural pattern was noted.

Animals↗
PubMed1992

Gene dosage and Down's syndrome: metabolic and enzymatic changes in PC12 cells overexpressing transfected human liver-type phosphofructokinase.

Down's syndrome (DS) is a human genetic disease caused by triplication of the distal third of chromosome 21 and overexpression of an unknown number of genes residing in it. The gene for the liver-type subunit of phosphofructokinase (PFKL), a key glycolytic enzyme, maps to this region and the product is overproduced in DS erythrocytes and fibroblasts. These facts, together with abnormalities which occur in DS glycolysis, make PFKL overexpression a candidate for causing some aspects of the DS phenotype. A cellular model for examining the consequences of PFKL overexpression in DS was constructed by transfecting rat PC12 cells with the human PFKL cDNA. Phosphofructokinase (PFK) isolated from PFKL-overexpressing clones was more inhibited by ATP and citrate and less activated by fructose-6-phosphate than control PFK; similar results were obtained when PFK preparations from DS and control fibroblasts were compared. In vivo NMR measurements determined that cells overexpressing PFKL performed glycolysis 40% faster than controls. These results show that overexpression of PFKL is the cause for altered biochemical regulatory characteristics of PFK in DS fibroblasts and can result in enhancement of glycolysis rates. It is also shown that increased gene dosage can exert its influence not merely by enhancing the amounts of gene products but also by altering their biochemical nature.

Adenosine Triphosphate↗
PubMed1991

Prophylaxis against organophosphate poisoning by an enzyme hydrolysing organophosphorus compounds in mice.

Parathion hydrolase purified from Pseudomonas sp. was injected i.v. into mice to demonstrate the feasibility of using organophosphorus acid anhydride (OPA) hydrolases as pretreatment against organophosphates (OP) poisoning. Results show that exogenous administration of as low as 7 to 26 micrograms of parathion hydrolase conferred protection against challenge with multiple median lethal doses (LD50) of diethyl p-nitrophenyl phosphate (paraoxon; 3.8-7.3 x LD50) and diethylfluorophosphate (DEFP; 2.9 x LD50) without administration of supportive drugs. The extent of protection observed was consistent with blood-parathion hydrolase levels and the kinetic constants of the enzymatic hydrolysis of paraoxon and DEFP by parathion hydrolase. OPA hydrolases not only appear to be potential prophylactic drugs capable of increasing survival ratio following OP intoxication but also to alleviate post-exposure symptoms.

Animals↗
PubMed1990

The structure of the human liver-type phosphofructokinase gene.

We have isolated the gene for the human liver-type phosphofructokinase, from upstream to the 5' mRNA terminus to beyond the polyadenylation site. The gene is at least 28 kb long and is divided into 22 exons; it contains conventional splice-junction sequences and one polyadenylation signal. Exons and introns are quite rich in G and C residues; some 60% of all nucleotides are either G or C. Five possible sites of polymorphism have been found. The gene structure reveals no signs of internal similarities despite protein sequence evidence which suggests that the PFK molecule is divided into two similar halves. The structure and organization of the human liver-type PFK gene are shown to be extremely similar to those of the rabbit muscle-type PFK.

Animals↗
PubMed1990

cDNA cloning of human oxysterol-binding protein and localization of the gene to human chromosome 11 and mouse chromosome 19.

Cellular cholesterol metabolism is regulated primarily through sterol-mediated feedback suppression of the activity of the low-density lipoprotein receptor and several enzymes of the cholesterol biosynthetic pathway. We previously described the cloning of a rabbit cDNA for the oxysterol-binding protein (OSBP), a cytosolic protein of 809 amino acids that may participate in these regulatory events. We now use the rabbit OSBP cDNA to clone the human OSBP cDNA and 5' genomic region. Comparison of the human and rabbit OSBP sequences revealed a remarkably high degree of conservation. The cDNA sequence in the coding region showed 94% identity between the two species, and the predicted amino acid sequence showed 98% identity. The human cDNA was used to determine the chromosomal localization of the OSBP gene by Southern blot hybridization to panels of somatic cell hybrid clones containing subsets of human or mouse chromosomes and by RFLP analysis of recombinant inbred mouse strains. The OSBP locus mapped to the long arm of human chromosome 11 and the proximal end of mouse chromosome 19. Along with previously mapped genes including Ly-1 and CD20, OSBP defines a new conserved syntenic group on the long arm of chromosome 11 in the human and the proximal end of chromosome 19 in the mouse.

Amino Acid Sequence↗