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von Langermann J Guterl JK Pohl M Wajant H Kragl U 《Bioprocess and biosystems engineering》2008,31(3):155-161
The application of unusual high pH-values within enzymatic cyanohydrin synthesis has been investigated. Usually enzymatic
cyanohydrin synthesis in two-phase systems requires low pH-values within the aqueous phase to suppress the non-enzymatic side
reaction. In contrast, we investigated the usage of pH-values above pH 6 by using the highly enantioselective (S)-selective hydroxynitrile lyase from Manihot esculenta. With these unusual reaction conditions also the unfavorable substrate 3-phenoxy-benzaldehyde can be converted by the wild
type enzyme with excellent conversion and enantiomeric excess yielding pure (S)-3-phenoxy-benzaldehyde cyanohydrin with an enantiomeric excess of 97%. Although the variant MeHNL–W128A shows a higher activity with respect to this reaction, the enantioselectivity was reduced (85% e.e.(S)). Additionally, a new continuous spectroscopic cyanohydrin assay monitoring the formation of 3-phenoxy-benzaldehyde cyanohydrin
was developed.
Dedicated to Prof. Dr. Christian Wandrey on the occasion of his 65th birthday. 相似文献
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D. F. Stiffler S. Eskandari 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(5):355-361
Larval and adult Ambystoma tigrinum were subjected to acidosis by infusing lactic acid (2 M·g-1) into the peritoneal cavity. Blood was sampled at intervals to establish the time-course of the ensuing acidosis. Both larvae and adults became significantly acidotic after 1 h. The larval acidosis was more pronounced (-4 pH units versus-2 pH units) than adults due to greater extracellular buffering capacity (higher [HCO3
-]) in adults. Both forms recovered in about 8 h. Larvae showed a typical increase in circulating norepinephrine during the initial stages of the acidosis; adults did not, having significantly lower norepinephrine titer than larvae during the acidosis. Both larvae and adults showed transient increases in PO2 during the acidosis. The 1 and 2 antagonists, timolol and butoxamine respectively, (0.2 g·g-1) were administered to separate groups of larvae. Butoxamine (2) delayed the recovery from the acidosis by prolonging the increase in arterial PCO2 and reversing the recovery of [HCO3
-]. Timolol (1) did not delay recovery. We conclude that 2 receptors are involved in the catecholamine responses to acidosis in larvae. Catecholamines appear not to play the same role in adult acid-base disturbances as they seem to in larvae.Abbreviations RBC
red blood cell 相似文献
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采用HRp-TMB-ST法,对小鼠延髓下橄榄核下端外侧网状核细胞的HRP-TMB反应产物影响因素分析表明:(1)较高的pH值(7.0以上)是反应产物消失的关键因素;0.2mol/LPB,pH5.0—6.0对HRP-TMB反应灵敏度、反应产物的稳定性及组织超微结构的保存是适宜的;当pH值相同时,缓冲液浓度不同,反应产物消失的程度和速度也不相同。(2)酒精有稳定反应产物的作用。(3)反应前的预浸、灌注液的成分、浓度和固定时间等则与反应产物的丢失无关。此外,用pH5.5和pH7.0的缓冲液处理的切片经DAB强化、锇化后,组织的超微结构无明显的差异。 相似文献
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In a beech (Fagus sylvatica L.) stand in north-west Germany vegetation of two transects (25m:1m and 20m:1m) was mapped and contents of macronutrients (Ca, Mg and K), micronutrients (Fe, Mn, Zn and Cu), and potentially phytotoxic metals (Pb, Cd, Ni and Al) were measured in different soil compartments and in roots, rhizomes, stems and leaves of two forest floor plant species (Mercurialis perennis L. and Polygonatum multiflorum L.). NH4Cl extractable cation contents, pH and other soil variables were also determined.The highest macronutrient contents could be found in the leaves of M. perennis and P. multiflorum. Heavy metals and Al accumulated in the roots. Correlation analysis suggests a considerable translocation of Zn and Cd between below- and above-ground organs of both investigated forest floor plants. No significant correlation was found between the contents of the other elements in the below- and above-ground parts.Available data indicate a considerable uptake by the plants not only of nutrients, but also of heavy metals from the upper mineral soil. Amounts of heavy metals and Al solubilized in the presence of NH4Cl increased with decreasing pH, whereas levels of soluble Ca and Mg were maximal at high pH-values of the extracts. It can be concluded that element uptake in the investigated plants is indirectly controlled by the pH of the upper mineral soil. 相似文献
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