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71.
The gpdA-promoter-controlled exocellular production of glucose oxidase (GOD) by recombinant Aspergillus niger NRRL-3 (GOD3-18) during growth on glucose and nonglucose carbon sources was investigated. Screening of various carbon substrates
in shake-flask cultures revealed that exocellular GOD activities were not only obtained on glucose but also during growth
on mannose, fructose, and xylose. The performance of A. niger NRRL-3 (GOD3-18) using glucose, fructose, or xylose as carbon substrate was compared in more detail in bioreactor cultures.
These studies revealed that gpdA-promoter-controlled GOD synthesis was strictly coupled to cell growth. The gpdA-promoter was most active during growth on glucose. However, the unfavorable rapid GOD-catalyzed transformation of glucose
into gluconic acid, a carbon source not supporting further cell growth and GOD production, resulted in low biomass yields
and, therefore, reduced the advantageous properties of glucose. The total (endo- and exocellular) specific GOD activities
were lowest when growth occurred on fructose (only a third of the activity that was obtained on glucose), whereas utilization
of xylose resulted in total specific GOD activities nearly as high as reached during growth on glucose. Also, the portion
of GOD excreted into the culture fluid reached similar high levels (≅ 90%) by using either glucose or xylose as substrate,
whereas growth on fructose resulted in a more pelleted morphology with more than half the total GOD activity retained in the
fungal biomass. Finally, growth on xylose resulted in the highest biomass yield and, consequently, the highest total volumetric
GOD activity. These results show that xylose is the most favorable carbon substrate for gpdA-promoter-controlled production of exocellular GOD. 相似文献
72.
Y. De Decker F. Baras 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(2):173-186
We study the dynamics of a class of catalytic surface
reactions in which an adsorbed molecule undergoes dissociation giving oxygen,
which then rapidly reacts with H adatoms to give water.
The reaction-diffusion equations predict bistability and explosive
transients similar to those observed in several low-pressure experiments.
Kinetic Monte Carlo simulations reveal however that the
dynamics can be strongly affected by spontaneous, inhomogeneous
fluctuations of composition on the surface. In particular,
bifurcation points can be displaced and the explosive character
of the transients can be lost, depending on a subtle balance between
the rate of reaction and the mobility of the decomposing species.
These effects can be quantified on the basis of
a stochastic formulation of the dynamics taking into account
spatial correlations.
This approach allows to better delimit
the applicability of the traditional
reaction-diffusion modelling in the case of reactions such as
the reduction of NO
x
or SO
x
species on catalytic surfaces. 相似文献
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Karsten Krohn 《Tetrahedron letters》1980,21(37):3557-3560
Naturally occurring quinones such as 7-methyljuglone, chrysophanol, emodin, helminthosporin, phomarin and physcion were prepared via Diels-Alder reaction and PCC-oxidation of the allylic alkohols obtained from the adducts. 相似文献
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The multiphoton ionization (MPI) spectrum of toluene arising from the 1B2 (1Lb) valence state has been investigated. The state participates as a two-photon resonance. A total of nine excited state fundamentals have been characterized, including three non-totally symmetric vibrations. The toluene MPI spectrum shows a strong resemblance to the two-photon fluorescence excitation spectrum with the strongest transitions taking place to the origin and excited state modes ν1(a1), ν12(a1) and ν14(b)2). The intensities of the observed fundamentals are rationalized in terms of Franck-Condon and vibronic coupling effects. A major conclusion is, that the primary mechanism for the activity of ν12 is vibronic coupling. 相似文献