Effect of Initial Cell Concentration on Ethanol Production by Flocculent Saccharomyces cerevisiae with Xylose-Fermenting Ability

Different initial cell concentrations of a recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated for their effects on xylose fermentation and glucose–xylose cofermentation. A high initial cell concentration greatly increased both the substrate utilization and ethanol production rates. During xylose fermentation, the highest rates of xylose consumption (2.58 g/L h) and ethanol production (0.83 g/L h) were obtained at an initial cell concentration of 13.1 g/L. During cofermentation, the highest rates of glucose consumption (14.4 g/L h), xylose consumption (2.79 g/L h), and ethanol production (6.68 g/L h) were obtained at an initial cell concentration of 12.7 g/L. However, a high initial cell density had no positive effect on the maximum ethanol concentration and ethanol yield mainly due to the increased amount of by-products including xylitol. The ethanol yield remained almost constant (0.34 g/g) throughout xylose fermentation (initial cell concentration range, 1.81–13.1 g/L), while it was slightly lower at high initial cell concentrations (9.87 and 12.7 g/L) during cofermentation. The determination of the appropriate initial cell concentration is necessary for the improvement of substrate utilization and ethanol yield.     

Overexpression of DnaJ-Like Chaperone Enhances Carotenoid Synthesis in <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis>

Production of functional carotenoids using microalgae may facilitate the commercialization of anti-aging nutritional supplements. The green alga Chlamydomonas reinhardtii uses a non-mevalonate (MEP) pathway for isopentenyl diphosphate (IPP) synthesis. Two enzymes thought to play important roles in this MEP pathway to IPP synthesis are 1-deoxy-d-xylulose 5-phosphate synthase (DXS) and reductase (DXR). DnaJ-like chaperone (Orange protein) is thought to support phytoene synthase, a key enzyme in plant carotenoid synthesis. Genes for Orange (OR), DXS, and DXR were overexpressed via nuclear transformation into C. reinhardtii. CDS of OR, DXS, and DXR were amplified and connected with dual promoters of heat-shock protein 70A and ribulose bisphosphate carboxylase small chain 2. Compared with the parental strain, transformant CrOR#2 produced increased lutein and β-carotene (1.9-fold and 1.7-fold per cell, respectively). Transformant CrDXS#1 produced lutein and β-carotene at lower per-cell abundances than those for the parental strain. CrDXR#2 transformant produced lutein and β-carotene at higher per-cell abundances than their parental counterpart; however, these transformants produced lutein and β-carotene at lower per-medium abundances than their parental counterparts. These results suggest that OR protein supports phytoene synthase in C. reinhardtii and that the phytoene synthesis step is rate-limiting in carotenoid synthesis.     

Enantioselective total synthesis of ustiloxin D

Ustiloxin D and phomopsin A are potent antimitotic agents that bind to tubulin and interfere with cellular microtubule function. A synthetic strategy has been developed to allow access to both of the natural products as well as a variety of variants of the ustiloxin and phomopsin family members in order to provide sufficient quantities for biological studies. Herein we report the enantioselective total synthesis of ustiloxin D using a longest linear sequence of 20 steps. Four of the five stereocenters were set using catalytic asymmetric methodologies. In particular, Evans's new Al-catalyzed asymmetric aldol reaction facilitated access to both syn and anti products corresponding to the different benzylic stereochemistries found in ustiloxins and phomopsins. In addition, due to its high functional group tolerance, Trost's Pd-mediated etherification was used to construct the chiral tertiary alkyl-aryl ether. Taken together, these synthetic strategies allow us to use densely functionalized intermediates to realize an efficient synthesis of ustiloxin D.     

Effects of the homogeneous Bi doping process on photoluminescence properties of YVO4:Bi,Eu nanophosphor

YVO₄:Bi³⁺,Eu³⁺ nanophosphors at a high Bi³⁺ concentration of 15 at% are synthesized from a Bi³⁺ source, nitrates of yttrium and europium(III), and sodium orthovanadate(V) by a low-temperature aqueous precipitation in the presence of citrate ions. When an ethylene glycol solution of bismuth(III) nitrate is used as a Bi³⁺ source, YVO₄:Bi³⁺,Eu³⁺ nanophosphors of ∼20 nm in size crystallize during aging at 85 °C without any by-products where the contents of Bi³⁺ and Eu³⁺ incorporated into crystalline YVO₄ are close to the respective nominal contents, as confirmed by transmission electron microscopy, X-ray diffractometry and X-ray fluorescent analysis. These nanophosphors show red emission corresponding to the f-f transition of Eu³⁺ under the excitation of Bi³⁺-V⁵⁺ charge transfer. When aging is continued after the completion of the crystallization, the photoluminescence intensity of nanophosphors reaches the constant value. This is the improved behavior in comparison to our previous work, where the photoluminescence intensity decreases after the prolonged aging because of the inhomogeneous doping of Bi³⁺ ions, and hence the concentration quenching.     

Angiotensin-converting enzyme inhibitors: synthesis and structure-activity relationships of potent N-benzyloxycarbonyl tripeptide inhibitors

A new series of gamma-D-Glu-containing N-benzyloxycarbonyl (Z) tripeptide inhibitors of angiotensin-converting enzyme (ACE) was synthesized. The effect of varying the antepenultimate amino acid residue in this series on the biological activity was studied. Introduction of Lys and Orn residues at the P1 position provided the most potent inhibitors, 25a and 25b (IC50: 3.5 and 4.9 x 10(-9) M, respectively), which exhibited an oral antihypertensive activity. This result suggests that basic amino acid residues at the P1 position play an important role in binding with the S1 subsite of ACE in this series. Oral antihypertensive activity of selected compounds was evaluated.     

Angiotensin-converting enzyme inhibitors: synthesis and biological activity of N-substituted tripeptide inhibitors

A new series of highly potent angiotensin-converting enzyme (ACE) inhibitors, 1-(N2-substituted L-lysyl-gamma-D-glutamyl)octahydro-1H-indole-2-carboxylic acids, was synthesized; various acyl groups were introduced at the alpha-amino group of the N-terminal P1 Lys. The effect of the N2-acyl groups on in vitro inhibitory activity and oral antihypertensive effect was examined. All of the synthesized N-acyl tripeptides were found to have in vitro inhibitory activity at an approximately nanomolar level, and showed antihypertensive potency in renal hypertensive rats at a dose of 10 mg/kg, when administered orally. Among them, compounds 7e, g and 9f, i, m showed potent and long-lasting antihypertensive effects compared with enalapril (2a). Their structure-activity relationships are also discussed.