Arabinose utilization by xylose-fermenting yeasts and fungi

Various wild-type yeasts and fungi were screened to evaluate their ability to fermentl-arabinose under oxygen-limited conditions when grown in defined minimal media containing mixtures ofl-ara-binose,d-xylose, andd-glucose. Although all of the yeasts and some of the fungi consumed arabinose, arabinose was not fermented to ethanol by any of the strains tested. Arabitol was the only major product other than cell mass formed froml-arabinose; yeasts converted arabinose to arabitol at high yield. The inability to fermentl-arabinose appears to be a consequence of inefficient or incomplete assimilation pathways for this pentose sugar.     

Formation of the main degradation compounds from arabinose,xylose, mannose and arabinitol during pyrolysis

The thermochemical behaviour of sugars (D- and DL-arabinose, D- and DL-xylose and D-mannose) and sugar alcohol (D- and DL-arabinitol) was investigated by TG and pyrolysis-gas chromatography with mass-selective detection (Py-GC/MSD). The temperature of pyrolysis was 500 and 550°C. The TG-curves were measured both in air and nitrogen atmospheres, from 25 to 700°C with the heating rate of 2°C min^-1. In each case, the main pyrolysis products were classified into the following compound groups: (i) furanes, (ii) pyranes, (iii) cyclopentanes, (iv) cyclohexanes, (v) anhydroglucopyranoses, (vi) dianhydroglucopyranoses and (vii) saturated fatty acids. For example, the main peaks of the chromatograms of pentoses (arabinose, xylose), hexose (mannose) and sugar alcohols (arabinitols) were different. The greatest peak of pentoses in gas-chromatogram was 2-furancarboxaldehyde and that of hexose was (2H)-furan-3-one. The greatest peak of arabinitols at pyrolysis temperature of 500°C was furan methanol and at 550°C a-angeligalactone. 5-hydroxymethyl-2-furan carboxaldehyde was found only in the pyrolysis of D-mannose (hexose). The former study showed that it was not found in pyrolysis of pentoses. The amount of CO₂ and H₂O was not determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

不同栽培方式对笋瓜（印度南瓜）果实中主要品质指标质量比的影响

以‘龙圆栗香’为试材,采用地爬式和架式两种种植方式,利用单干、双干和三干3种整枝方式,研究不同栽培方式对笋瓜果实中果胶、戊糖和铬（Cr3＋）3种主要品质指标质量比的影响.结果表明：两种种植方式下三干整枝方式均不利于果实中果胶和戊糖的积累,地爬式栽培比架式栽培有利于果实中铬（Cr3＋）的积累;地爬式栽培双干整枝处理下果实内果胶质量比最高.可采用架式单干整枝处理方式来提高单位面积笋瓜果实中果胶、铬（Cr3＋）和戊糖的产量.     

Glucose 6-Phosphate Dehydrogenase from Trypanosomes: Selectivity for Steroids and Chemical Validation in Bloodstream Trypanosoma brucei

Glucose 6-phosphate dehydrogenase (G6PDH) fulfills an essential role in cell physiology by catalyzing the production of NADPH⁺ and of a precursor for the de novo synthesis of ribose 5-phosphate. In trypanosomatids, G6PDH is essential for in vitro proliferation, antioxidant defense and, thereby, drug resistance mechanisms. So far, 16α-brominated epiandrosterone represents the most potent hit targeting trypanosomal G6PDH. Here, we extended the investigations on this important drug target and its inhibition by using a small subset of androstane derivatives. In Trypanosoma cruzi, immunofluorescence revealed a cytoplasmic distribution of G6PDH and the absence of signal in major organelles. Cytochemical assays confirmed parasitic G6PDH as the molecular target of epiandrosterone. Structure-activity analysis for a set of new (dehydro)epiandrosterone derivatives revealed that bromination at position 16α of the cyclopentane moiety yielded more potent T. cruzi G6PDH inhibitors than the corresponding β-substituted analogues. For the 16α brominated compounds, the inclusion of an acetoxy group at position 3 either proved detrimental or enhanced the activity of the epiandrosterone or the dehydroepiandrosterone derivatives, respectively. Most derivatives presented single digit μM EC₅₀ against infective T. brucei and the killing mechanism involved an early thiol-redox unbalance. This data suggests that infective African trypanosomes lack efficient NADPH⁺-synthesizing pathways, beyond the Pentose Phosphate, to maintain thiol-redox homeostasis.     

SO2 prehydrolysis for high yield ethanol production from biomass

The advantages of the use of SO₂ in steam pretreatment are described. Two different large scale continuous reactors, the Stake and the Wenger, have been used for this purpose. Pine, aspen and corn stover were prehydrolysed by SO₂ in these reactors and hydrolysed by enzymes. The solution of hexoses and pentoses so obtained were fermented byPichia stipitis R, yielding 372, 346 and 388 L ethanol/tonne for the 3 feedstocks, respectively. When a mixed culture ofP. stipitis R, which is an excellent pentose fermenter, andBrettanomyces clausenii which is an excellent cellobiose fermenter, was used in a simultaneous saccharification-fermentation made with SO₂-prehydrolysed aspen, the yield rose to 384 L/tonne. These are higher yields than have been reported in the literature to date.     

Purification and properties of xylitol dehydrogenase from the xylose-fermenting yeastCandida shehatae

Xylitol dehydrogenase (EC1.1.1.9) from xylose-grown cells ofCandida shehatae was purified 215-fold by sequential chromatography on NAD-C8 affinity, Superose-12, and Cibacron blue columns, and a single band was observed by SDS gel electrophoresis. The purified enzyme had a native molecular weight of 82 kDa and a denatured molecular weight of 40 kDa following SDS gel electrophoresis, indicating that it was composed of two subunits. Alcohol dehydrogenase copurified on the NAD-C8 but was substantially removed by Superose-12 and was not detected following Cibacron blue chromatography. The kinetic properties of the C.shehatae xylitol dehydrogenase differed considerably from those described previously for thePachysolen tannophilus enzyme. The K_m of the C.shehatae enzyme for xylitol was 3.8 times smaller, whereas the K_m for xylulose was 1.7-fold bigger. These factors could account for the lower xylitol production by C.shehatae.