Characterization of the Entamoeba histolytica Ornithine Decarboxylase-Like Enzyme

Background: The polyamines putrescine, spermidine, and spermine are organic cations that are required for cell growth and differentiation. Ornithine decarboxylase (ODC), the first and rate-limiting enzyme in the polyamine biosynthetic pathway, is a highly regulated enzyme. Methodology and Results: To use this enzyme as a potential drug target, the gene encoding putative ornithine decarboxylase (ODC)-like sequence was cloned from Entamoeba histolytica, a protozoan parasite causing amoebiasis. DNA sequence analysis revealed an open reading frame (ORF) of similar to 1,242 bp encoding a putative protein of 413 amino acids with a calculated molecular mass of 46 kDa and a predicted isoelectric point of 5.61. The E. histolytica putative ODC-like sequence has 33% sequence identity with human ODC and 36% identity with the Datura stramonium ODC. The ORF is a single-copy gene located on a 1.9-Mb chromosome. The recombinant putative ODC protein (48 kDa) from E. histolytica was heterologously expressed in Escherichia coli. Antiserum against recombinant putative ODC protein detected a band of anticipated size similar to 46 kDa in E. histolytica whole-cell lysate. Difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ODC, had no effect on the recombinant putative ODC from E. histolytica. Comparative modeling of the three-dimensional structure of E. histolytica putative ODC shows that the putative binding site for DFMO is disrupted by the substitution of three amino acids-aspartate-332, aspartate-361, and tyrosine-323-by histidine-296, phenylalanine-305, and asparagine-334, through which this inhibitor interacts with the protein. Amino acid changes in the pocket of the E. histolytica enzyme resulted in low substrate specificity for ornithine. It is possible that the enzyme has evolved a novel substrate specificity. Conclusion: To our knowledge this is the first report on the molecular characterization of putative ODC-like sequence from E. histolytica. Computer modeling revealed that three of the critical residues required for binding of DFMO to the ODC enzyme are substituted in E. histolytica, resulting in the likely loss of interactions between the enzyme and DFMO.

Regulation of hepatic cholesterolgenesis by ubiquinone

The concentration of liver ubiquinone increased progressively with the time of feeding ubiquinone, and this increase was reflected in all the cell fractions. 2. 2. Inhibition of sterol synthesis by ubiquinone was exerted only in the liver, not in the kidney or intestine. 3. 3. Extending the period of feeding ubiquinone or increasing the concentration of ubiquinone fed had no effect on the extent of inhibition. 4. 4. Inhibition was found to be specific to ubiquinone-9, the natural major homologue in the rat liver; other homologues were ineffective. 5. 5. The site of inhibition by ubiquinone was indicated to be between acetyl-CoA and mevalonate, since there was no change in fatty acid and ketone body synthesis in ubiquinone-fed animals as compared to normal animals.

Oxidation of vitamin A1 and vitamin A2 aldehydes to the corresponding acids by enzymes from pig and rat livers

VITAMIN A is stored in rat liver largely as its ester with small amounts of the alcohol, but is transported in the normal circulating blood in the latter form1. Although it was generally believed that the alcohol form is the more physiological state of the vitamin, since the work of Dowling and Wald2, it is being recognized that vitamin A acid and not the alcohol may be nearer to the 'active vitamin A'. If this were to be so, it would be important to demonstrate that a mechanism exists in the rat for the production of vitamin A acid from vitamin A alcohol through the intermediate, the aldehyde. Regarding the formation of the aldehyde, it has been well established that the alcohol dehydrogenase can bring about the conversion of vitamin A alcohol to retinene3. The presence of an enzyme in rat and pig liver catalysing the oxidation of retinene1 and retinene2 to the corresponding acids has been demonstrated in the present work and the partially purified enzyme preparation shown to be completely devoid of alcohol dehydrogenase activity.

An evaluation of rate-controlling obstacles for low-temperature deformation of zirconium

The low-temperature plastic flow of alpha-zirconium was studied by employing constantrate tensile tests and differential-stress creep experiments. The activation parameters, enthalpy and area, have been obtained as a function of stress for pure, as well as commercial zirconium. The activation area is independent of grain size and purity and falls to about 9b2 at high stresses. The deformation mechanism below about 700° K is found to be controlled by a single thermally activated process, and not a two-stage activation mechanism. Several dislocation mechanisms are examined and it is concluded that overcoming the Peierls energy humps by the formation of kink pairs in a length of dislocation is the rate-controlling mechanism. The total energy needed to nucleate a double kink is about 0.8 eV in pure zirconium and 1 eV in commercial zirconium

Structure of 5-methyl-2'-deoxycytidine 5'-monophosphate dihydrate

CloHI6N307P.2H20 , Mr = 357.2, triclinic, P1, a = 4-8520 (8), b = 8"3703 (8), c = 10.0199 (12) A, a= 104.578 (9),/3= 102.332 (13), 7=93.670(11) o, V = 381"75 A 3, Z = 1, Dx = 1"55, Dm = 1"53 Mg m -3, a(Cu Ka) = 1.5418 A,/z = 2.01 mm- l, F(000) = 188, T= 290 K, R = 0-049 for 1568 unique reflections.

Photochemistry of .alpha.,.beta.-unsaturated thiones: addition to electron-rich olefins from T1

1,1,3-Trimethyl-2-thioxo-1,2-dihydronaphthale(1n)e adds to electron-rich olefins upon excitation to either Sz (PP*) or Sl (ns*) states. Excitation to S2 level resulted in the same mixture of products, namely thietane and 1,4-dithiane, as on excitation to S1 level. Addition occurs to the thiocarbonyl function and not to the carbon-carbon double bond. The addition is site-specific, and the formation of thietane is regiospecific. The ratio of thietane to 1,4-dithiane in the product mixture is dependent on the concentration of the thioenone. The addition is suggested to originate from the lowest triplet state (Tl) and involves diradical intermediates.

Photochemistry of .alpha.,.beta.-unsaturated thiones. Cycloaddition to electron-deficient olefins from higher excited states

Electron-deficient olefins add to thioenone 1 upon m* excitation. Cycloaddition occurs to the thiocarbonyl chromophore preferentially from the less-hindered side to yield thietanes. Thietane formation is stereospecific and regioselective. This addition has been inferred to originate from the second excited singlet, S2(?rx*), state. The exciplex intermediacy has been inferred from the dependence of the fluorescence quenching rate constant on the electron-acceptor properties of the olefin. The observed site specificity and regioselectivity are rationalized on the basis of PMO theory. The observed photochemical behavior of thioenone is different from that of enones.

A MAS NMR investigation of aluminosilicate, silicophosphate, and aluminosilicophosphate gels and the evolution of crystalline structures on heating the gels

Gels of various composition containing SiO2, Al2O3, and P2O5 have been investigated by employing high resolution magic-angle-spinning (MAS) 27Al, 29Si, and 31P NMR spectroscopy. Changes occurring in the NMR spectra as the gels are progressively heated have been examined to understand the nature of structural changes occurring during the crystallization of the gels. 27Al resonance is sensitive to changes in the coordination number even when the Al concentration is as low as 1 mol%. As the percentage of Al increases, the hydroxyl groups tend to be located on the Al sites while Si remains as SiO4/2 (Q4). Mullite is the major phase formed at higher temperature in the aluminosilicate gels. In the case of the silicophosphate gels, Si is present in the form of Q4 and Q3 species. There is a change in the coordination of Si from four to six as the gel is heated. The formation of six-coordinated Si is facilitated even at lower temperatures (~673 K) when the P2O5 content is high. The phosphorus atoms present as orthophosphoric acid units in the xerogels change over to metaphosphate-like units as the gel is heated to higher temperatures. In aluminosilicophosphates, Si is present as Q4 and Q3 species while P is present as metaphosphate units; Al in these gels seems to be inducted into the tetrahedral network positions.

Thermal decomposition of zirconyl oxalates I. Barium zirconyl oxalate

Conditions for the preparation of stoichiometric barium zirconyl oxalate heptahydrate (BZO) have been standardized. The thermal decomposition of BZO has been investigated employing TG, DTG and DTA techniques and chemical and gas analysis. The decomposition proceeds through four steps and is not affected much by the surrounding gas atmosphere. Both dehydration and oxalate decomposition take place in two steps. The formation of a transient intermediate containing both oxalate and carbonate groups is inferred. The decomposition of oxalate groups results in a carbonate of composition Ba2Zr2OsCO3, which decomposes between 600 and 800 ~ and yields barium zirconate. Chemical analysis, IR spectra and X-ray powder diffraction data support the identity of the intermediate as a separate entity.

Thermal decomposition of zirconyl oxalates I. Barium zirconyl oxalate

Conditions for the preparation of stoichiometric barium zirconyl oxalate heptahydrate (BZO) have been standardized. The thermal decomposition of BZO has been investigated employing TG, DTG and DTA techniques and chemical and gas analysis. The decomposition proceeds through four steps and is not affected much by the surrounding gas atmosphere. Both dehydration and oxalate decomposition take place in two steps. The formation of a transient intermediate containing both oxalate and carbonate groups is inferred. The decomposition of oxalate groups results in a carbonate of composition Ba2Zr2O5CO3, which decomposes between 600 and 800° and yields barium zirconate. Chemical analysis, IR spectra and X-ray powder diffraction data support the identity of the intermediate as a separate entity.Die Bedingungen für die Herstellung von stöchiometrischem Barium-zirconyl-oxalat Heptahydrat (BZO) wurden standardisiert. Die thermische Zersetzung von BZO wurde unter Einsatz der TG-, DTG- und DTA, sowie der chemischen und Gasanalyse untersucht. Die Zersetzung verläuft über vier Stufen und wird von der umgebenden Gasathmosphäre nicht besonders beeinflusst. Sowohl die Dehydratisierung als auch die Oxalatzersetzung erfolgt in zwei Stufen. Die Bildung einer intermediären Übergangsverbindung mit sowohl Oxalat- als auch Carbonatgruppen wirken hierbei mit. Die Zersetzung der Oxalatgruppen ergibt ein Carbonat der Zusammensetzung Ba2Zr2O5CO3, das zwischen 600 und 800° zersetzt wird und Bariumzirconat ergibt. Die Angaben der chemischen Analyse, der IR-Spekren und der Röntgen-Pulver-Diffraktion unterstützen die Identität der Intermediärverbindung als eine separate Einheit.On a standardisé les conditions de préparation de l'oxalate heptahydraté de zirconyle et de baryum (BZO) stoechiométrique. On a étudié la décomposition thermique de BZO par TG, TGD et ATD ainsi que par analyses chimiques et analyses des gaz. La décomposition a lieu en quatre étapes et n'est pas trop influencée par l'atmosphère ambiante. La déshydratation et la décomposition de l'oxalate ont lieu en deux étapes. Il se forme un composé intermédiaire de transition contenant à la fois les groupes oxalate et carbonate. La décomposition des groupes oxalate fournit un carbonate de composition Ba2Zr2O5CO3 qui se décompose entre 600 et 800° pour fournir du zirconate de baryum. L'analyse chimique, les spectres IR et la diffraction des rayons X sur poudre, apportent les preuves de l'existence d'un composé intermédiaire comme entité séparée.

K1-xLaxCa2-xNb3O10, a Layered Perovskite Series with Variable Interlayer Cation Density, and LaCaNb3O10, a Novel Layered Perovskite Oxide with No Interlayer Cations

A series of layered perovskite oxides of the formula K1-xLaxCa2-xNb3O10 for 0 < x ≤ 1.0 have been prepared. All the members are isostructural, possessing the structure of KCa2Nb3O10. The interlayer potassium ions in the new series can be ion-exchanged with protons to give H1-xLaxCa2-xNb3O10. The latter readily forms intercalation compounds of the formula (CnH2n+1NH3)1-x LaxCa2-xNb3O10, just as the parent solid acid HCa2Nb3O10. The end member LaCaNb3O10 containing no interlayer cations is a novel layered perovskite oxide, being a n = 3 member of the series An-1BnX3n+1.

On infinitesimal σ-fields generated by random processes

It is proved that the infinitesimal look-ahead and look-back σ-fields of a random process disagree at atmost countably many time instants.

Synthesis of (±)-thaps-7(15)-ene and (±)-thaps-6-enes

The synthesis of (±)-3a,4,4,7a-tetramethylhydrindan-2-one 8, containing three contiguous quaternary carbons as present in thapsanes, and the total synthesis of thaps-7(15)-ene 6 and thaps-6-ene 7, probable biogenetic precursors of thapsanes, have been achieved. Thus, orthoester Claisen rearrangement of cyclogeraniol 14, followed by hydrolysis of the resultant ester 16 furnished the eneacid 13. Copper sulfate-catalysed intramolecular cyclopropanation of the diazo ketone 18, derived from the acid 13, generated the cyclopropyl ketone 12. Regiospecific reductive cleavage of cyclopropyl ketone 12 furnished the hydrindanone 8, whereas the diazo ketone 26 furnished the hydrindanone 28avia the cyclopropyl ketone 27. Wittig methylenation of the hydrindanone 28a furnished thaps-7(15)-ene 6, which on isomerisation gave thaps-6-ene 7. Allylic oxidation of thaps-6-ene furnished the thapsenone 31, a degradation product of the natural thapsane 1b.