Expression of active yeast pyruvate decarboxylase in Escherichia coli

We have shown by appropriate modification of the translational signals and using the strong T7 RNA polymerase promoter phi 10, that a cloned Saccharomyces cerevisiae pyruvate decarboxylase gene (pdc1) can be expressed in Escherichia coli. This protein, which migrated as a single band on SDS-polyacrylamide gels, was found to have a subunit molecular mass of approximately 62 kDa, similar to that of the enzyme produced by yeast. Polyclonal antibodies raised against purified yeast pyruvate decarboxylase recognized this bacterially produced protein. We found that this recombinant enzyme is active, indicating that the homotetramer encoded by the pdc1 gene is functional

Effects of substitution of aspartate-440 and tryptophan-487 in the thiamin diphosphate binding region of pyruvate decarboxylase from Zymomonas mobilis

A tryptophan residue at position 487 in Zymomonas mobilis pyruvate decarboxylase was altered to leucine by site-directed mutagenesis. This modified Z. mobilis pyruvate decarboxylase was active when expressed in Escherichia coli and had unchanged kinetics towards pyruvate. The enzyme showed a decreased affinity for the cofactors with the half-saturating concentrations increasing from 0.64 to 9.0 μM for thiamin diphosphate and from 4.21 to 45 μM for Mg2+. Unlike the wild-type enzyme, there was little quenching of tryptophan fluorescence upon adding, cofactors to this modified form. The data suggest that tryptophan-487 is close to the cofactor binding site but is not required absolutely for pyruvate decarboxylase activity. Substitution of asparagine, threonine of glycine for aspartate-440, a residue which is conserved between many thiamin diphosphate-dependent enzymes, completely abolishes enzyme activity

Regularly Distributed and Fully Accessible Pt Nanoparticles in Silica Pore Channels via the Controlled Growth of a Mesostructured Matrix around Pt Colloids

SSCI+PDEInternational audienceMerging a colloidal approach for the synthesis of Pt nanoparticles and a supramolecular pathway for generating mesostructured oxides can provide via a one-pot synthesis a well-defined, active, and stable heterogeneous catalyst. This material contains regularly distributed Pt nanoparticles along the channel pores of a highly ordered silica matrix

Reconstructing Early Pleistocene (1.3Ma) terrestrial environmental change in western Anatolia: Did it drive fluvial terrace formation?

A terrestrial environmental reconstruction of an Early Pleistocene landscape from western Anatolia is presented. The basis of this reconstruction is a sedimentary stack comprising fluvial and colluvial slope deposits. Contained within this stack is a sequence comprising two massive laminar calcretes alternating with three reddish palaeosols. This evolutionary sequence is situated on top of a fluvial terrace staircase capped by a 1.3 Ma (40Ar/39Ar plateau age) lava flow. The micro-morphological properties of the observed calcretes and reddish palaeosols combined with the stable oxygen and carbon isotopic composition of the carbonates suggest the alternation of three stable relatively warm–humid (vegetation rich) and two stable relatively arid–cool (bare surface) cycles. In addition, there is also ample evidence for landscape instability in between these phases causing local soil truncation and slope instability in an open grassland–shrub environment. These landscape instability phases match well with known fluvial incisional phases of the Gediz during this period. This suggests that climate-forced landscape environmental dynamics were of sufficient magnitude to drive fluvial terrace formation of the Early Pleistocene Gediz

Factors underlying the recovery potential of littoral seagrass in the Dutch Wadden Sea

In de Waddenzee komen twee soorten zeegras voor, namelijk klein zeegras (Zostera noltii) en groot zeegras (Zostera marina). Beide soorten kunnen een eenjarige en een meerjarige levenscyclus vertonen, waarbij ze respectievelijk met zaden en wortelstokken de winter overleven. Na een periode van zeer lage abundantie, als gevolg van ziekten in de jaren dertig en eutrofiëring in de jaren tachtig, lijkt het zeegras in de noordelijke delen van de trilaterale Waddenzee zich te herstellen, onder meer als het resultaat van een verbetering van de waterkwaliteit. In de zuidelijke delen van de Waddenzee zijn zeegrasvelden echter nog schaars en hebben ze een lage dichtheid. Hoewel zeegras in de Nederlandse Waddenzee enig herstel leek te hebben doorgemaakt, is het huidige oppervlak van de zeegrasvelden (ca. 3 km2) nog steeds maar een fractie (<3%) van het oppervlak dat geschikt lijkt te zijn voor het voorkomen van zeegras (ongeveer 130 km2). Dit vraagt om nader onderzoek naar omgevingsfactoren die de uitbreiding van zeegras in de Nederlandse Waddenzee mogelijk beperken

Volcanic disruption and drainage diversion of the palaeo-Hudut River, a tributary of the Early Pleistocene Gediz River, Western Turkey

The importance of extrinsic drivers of fluvial system behaviour (climate, tectonics, eustatic sea level) over Quaternary timescales is well documented. However, comparatively fewer studies have been reported concerning the significance of more localised changes at reach to sub-catchment scale, over these extended (10exp4–10exp6 years) timescales. In this paper we examine the Early Pleistocene sedimentary record of the palaeo-Hudut River and compare it with the record from the trunk river into which it drains, the Gediz River of Western Turkey. Both the Gediz River and the Hudut River were subjected to major localised disruption during the Early Pleistocene as a consequence of volcanism but their respective responses to these events appear to differ. Observations are reported from the sedimentary sequence buried beneath the lavas which cap the Burgaz plateau. These sediments record a remarkable amount of detail for a significant period of the Early Pleistocene. These suggest that the palaeo-Hudut system responded largely to the creation and failure of downstream lava dams, both through channel incision and subsequent filling, and via route diversions around lava dams and their associated lakes. In contrast, the Gediz terrace record appears to demonstrate a river which was able to accommodate these changes more readily and hence, continue to undergo sedimentation–incision cycles consistent with a climate forcing