Reductive activation of the coenzyme A/acetyl-CoA isotopic exchange reaction catalyzed by carbon monoxide dehydrogenase from Clostridium thermoaceticum and its inhibition by nitrous oxide and carbon monoxide

The final steps in the synthesis of acetyl-CoA by CO dehydrogenase (CODH) have been studied by following the exchange reaction between CoA and the CoA moiety of acetyl-CoA. This reaction had been studied earlier (Pezacka, E., and Wood, H. G. (1986) J. Biol. Chem. 261, 1609-1615 and Ramer, W. E., Raybuck, S. A., Orme-Johnson, W. H., and Walsh, C. T. (1989) Biochemistry 28, 4675-4680). The CoA/acetyl-CoA exchange activity was determined at various controlled redox potentials and was found to be activated by a one-electron reduction with half-maximum activity occurring at -486 mV. There is approximately 2000-fold stimulation of the exchange by performing the reaction at -575 mV relative to the rate at -80 mV. Binding of CoA to CODH is not sensitive to the redox potential; therefore, the reductive activation affects some step other than association/dissociation of CoA. We propose that a metal center on CODH with a midpoint reduction potential of less than or equal to -486 mV is activated by a one-electron reduction to cleave the carbonyl-sulfur bond and/or bind the acetyl group of acetyl-CoA. Based on a comparison of the redox dependence of this reaction with that for methylation of CODH (Lu, W-P., Harder, S. R., and Ragsdale, S. W. (1990) J. Biol. Chem. 265, 3124-3133) and CO2 reduction and formation of the Ni-Fe-C EPR signal (Lindahl, P. A., Münck, E., and Ragsdale, S. W. (1990) J. Biol. Chem. 265, 3873-3879), we propose that the assembly of the acetyl group of acetyl-CoA, i.e. binding the methyl group of the methylated corrinoid/iron-sulfur protein, binding CO, and methyl migration to form the acetyl-CODH intermediate, occur at the novel Ni-Fe3-4-containing site in CODH. CO has two effects on the CoA/acetyl-CoA exchange: it activates the reaction due to its reductive capacity and its acts as a noncompetitive inhibitor. We also discovered that the CoA/acetyl-CoA exchange was inhibited by nitrous oxide via an oxidative mechanism. In the presence of a low-potential electron donor, CODH becomes a nitrous oxide reductase which catalytically converts N2O to N2. This study combined with earlier results (Lu, W-P., Harder, S. R., and Ragsdale, S. W. (1990) J. Biol. Chem. 265, 3124-3133) establishes that the two-subunit form of CODH is completely active in all reactions known to be catalyzed by CODH.     

Phenology of first and peak emergence of Aphthona lacertosa and A. nigriscutis: Two flea beetles introduced for biological control of leafy spurge, Euphorbia esula L.

Nonlinear models were used to estimate first emergence and peak abundance dates for Aphthona lacertosa Rosenhauer and A. nigriscutis Foudras, two flea beetles introduced to control leafy spurge, Euphorbia esula L., in North America. For model development, 26 field sites were sampled for flea beetle abundance at weekly intervals for eight weeks in three western Minnesota counties in 2000, 2001, and 2002. A three-parameter Weibull function, fit to observed cumulative probability distributions, were used to predict accumulated degree-days (ADD) to first emergence. Bias testing indicated the Weibull function provided a useful estimate of first emergence for A. lacertosa (304 ADD, lower developmental threshold 7.5 °C), but failed to produce a useful estimate for A. nigriscutis. A third-order polynomial was used to approximate seasonal abundance and predict peak abundance for each species. Estimated ADD to peak abundance of A. lacertosa was 594 ± 24 (DD > 7.5 °C) and 670 ± 15 (DD > 9.3 °C) for A. nigriscutis. Models were validated with additional data sets from Minnesota, Montana, and North Dakota. Estimated date of peak emergence provided useful predictions of peak emergence for Minnesota and North Dakota, but failed to predict peak emergence in Montana. We speculate that variation in climate and environmental conditions between Midwestern states and Montana were responsible for differing emergence patterns. We conclude that phenology models should be developed regionally to provide useful predictions of peak emergence for land managers. Maps were developed for Minnesota to spatially display predicted dates of peak abundance for A. lacertosa and A. nigriscutis.     

Three new species of Pristionchus (Nematoda: Diplogastridae) show morphological divergence through evolutionary intermediates of a novel feeding‐structure polymorphism

Developmental plasticity is often correlated with diversity and has been proposed as a facilitator of phenotypic novelty. Yet how a dimorphism arises or how additional morphs are added is not understood, and few systems provide experimental insight into the evolution of polyphenisms. Because plasticity correlates with structural diversity in Pristionchus nematodes, studies in this group can test the role of plasticity in facilitating novelty. Here, we describe three new species, Pristionchus fukushimae sp. nov. , Pristionchus hoplostomus sp. nov. , and the hermaphroditic Pristionchus triformis sp. nov. , which are characterized by a novel polymorphism in their mouthparts. In addition to showing the canonical mouth dimorphism of diplogastrid nematodes, comprising a stenostomatous (‘narrow‐mouthed’) and a eurystomatous (‘wide‐mouthed’) form, the new species exhibit forms with six, 12, or intermediate numbers of cheilostomatal plates. Correlated with this polymorphism is another trait that varies among species: whereas divisions between plates are complete in P. triformis sp. nov. , which is biased towards a novel ‘megastomatous’ form comprising 12 complete plates, the homologous divisions in the other new species are partial and of variable length. In a reconstruction of character evolution, a phylogeny inferred from 26 ribosomal protein genes and a partial small subunit rRNA gene supported the megastomatous form of P. triformis sp. nov. as the derived end of a series of split‐plate forms. Although split‐plate forms were normally only observed in eurystomatous nematodes, a single 12‐plated stenostomatous individual of P. hoplostomus sp. nov. was also observed, suggesting independence of the two types of mouth plasticity. By introducing these new species to the Pristionchus model system, this study provides further insight into the evolution of polymorphisms and their evolutionary intermediates. © 2013 The Linnean Society of London     

Three‐dimensional reconstruction of the stomatostylet and anterior epidermis in the nematode Aphelenchus avenae (Nematoda: Aphelenchidae) with implications for the evolution of plant parasitism

A three‐dimensional model of the stomatostylet and associated structures has been reconstructed from serial thin sections of Aphelenchus avenae, a representative of Tylenchomorpha, a group including most plant parasitic nematodes. The reconstruction is compared with previous work on bacteriovorous cephalobids and rhabditids to better understand the evolution of the stylet and its associated cells. Two arcade syncytia (“guide ring”) line the stylet shaft, supporting the hypothesis that the stylet shaft and cone (into which the shaft extends and which is not lined by syncytia) are homologous with the gymnostom of cephalobids, the sister taxon of tylenchids. Epidermal syncytia, HypA, HypB, HypC, and HypE, line the cephalic framework, vestibule, and vestibule extension, congruent with the hypothesis that these components are homologous with the cephalobid cheilostom. Relative to outgroups, HypC is expanded in A. avenae, enclosing sensilla that fill most of the cephalic framework. The homolog of syncytium HypD in the cephalobid Acrobeles complexus is not observed in A. avenae. Arcade syncytia are reduced compared with those of cephalobids. Stylet protractor muscles in A. avenae are homologous with the most anterior set of radial muscles of cephalobids. Observations to date test and verify our previous hypotheses of homology of the stomatostylet with respect to the stoma of bacteriovorous outgroups. Reconstruction of the stegostom and pharynx will provide further tests of homology and evolution of feeding structure adaptations for plant parasitism. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Leptojacobus dorci n. gen., n. sp. (Nematoda: Diplogastridae), an Associate of Dorcus Stag Beetles (Coleoptera: Lucanidae)

A new species of diplogastrid nematode, Leptojacobus dorci n. gen., n. sp., was isolated from adults of the stag beetle Dorcus ritsemae (Coleoptera: Lucanidae) that were purchased from a pet shop in Japan. Leptojacobus n. gen. is circumscribed by a very thin, delicate body and by a small stoma with minute armature. A combination of other stomatal characters, namely the division of the cheilostom into adradial plates, the symmetry of the subventral stegostomatal sectors, and the presence of a thin, conical dorsal tooth, further distinguishes Leptojacobus n. gen. from other genera of Diplogastridae. Phylogenetic analysis of nearly full-length SSU rRNA sequences support the new species, together with an isolate identified previously as Koerneria luziae, to be excluded from a clade including all other molecularly characterized diplogastrids with teeth and stomatal dimorphism. Therefore, the new species will be of importance for reconstruction of ancestral character histories in Diplogastridae, a family circumscribed by a suite of feeding-related novelties.     

The role of an iron-sulfur cluster in an enzymatic methylation reaction. Methylation of CO dehydrogenase/acetyl-CoA synthase by the methylated corrinoid iron-sulfur protein

This paper focuses on how a methyl group is transferred from a methyl-cobalt(III) species on one protein (the corrinoid iron-sulfur protein (CFeSP)) to a nickel iron-sulfur cluster on another protein (carbon monoxide dehydrogenase/acetyl-CoA synthase). This is an essential step in the Wood-Ljungdahl pathway of anaerobic CO and CO2 fixation. The results described here strongly indicate that transfer of methyl group to carbon monoxide dehydrogenase/acetyl-CoA synthase occurs by an SN2 pathway. They also provide convincing evidence that oxidative inactivation of Co(I) competes with methylation. Under the conditions of our anaerobic assay, Co(I) escapes from the catalytic cycle one in every 100 turnover cycles. Reductive activation of the CFeSP is required to regenerate Co(I) and recruit the protein back into the catalytic cycle. Our results strongly indicate that the [4Fe-4S] cluster of the CFeSP is required for reductive activation. They support the hypothesis that the [4Fe-4S] cluster of the CFeSP does not participate directly in the methyl transfer step but provides a conduit for electron flow from physiological reductants to the cobalt center.     

Current status of antisense DNA methods in behavioral studies

The antisense DNA method has been used successfully to block the expression of specific genes in vivo in neuronal systems. An increasing number of studies in the last few years have shown that antisense DNA administered directly into the brain can modify various kinds of behaviors. These findings strongly suggest that the antisense DNA method can be used as a powerful tool to study causal relationships between molecular processes in the brain and behavior. In this article we review the current status of the antisense method in behavioral studies and discuss its potentials and problems by focusing on the following four aspects; (i) optimal application paradigms of antisense DNA methods in behavioral studies; (ii) efficiencies of different administration methods of antisense DNA used in behavioral studies; (iii) determination of specificity of behavioral effects of antisense DNA; and (iv) discrepancies between antisense DNA effects on behaviors and those on protein levels of the targeted gene.      

THE RATE OF GROWTH OF THE DAIRY COW : II. GROWTH IN WEIGHT AFTER THE AGE OF TWO YEARS.

An extensive amount of data is presented on the growth in weight of the dairy cow from 2 to 17 years of age, covering practically the entire duration of life. The data show that after the age of 2 years the rate of growth declines in a non-cyclic manner. The course of decline in growth follows the course of decline of a monomolecular chemical reaction; that is, the percentage decline in growth with age is constant.