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71.
Triantafyllos Roukas 《Applied biochemistry and biotechnology》1998,74(1):43-53
The production of citric acid from carob pod extract byA. niger in surface fermentation was investigated. A maximum citric acid concentration (85.5 g/L), citric acid productivity (4.07
g/L/d), specific citric acid production rate (0.18 g/g/d), and specific sugar uptake rate (0.358 g/g/d) was achieved at an
initial sugar concentration of 200 g/L, pH of 6.5, and a temperature of 30°C. Other kinetic parameters, namely, citric acid
yield, biomass yield, specific biomass production rate, and fermentation efficiency were maximum at pH 6.5, temperature 30°C,
and initial sugar concentration 100 g/L. The external addition of methanol into the carob pod extract at a concentration up
to 4% (v/v) improved the production of citric acid. 相似文献
72.
73.
Arginase isolated from beef liver was covalently attached to a polyacrylamide bead support bearing carboxylic groups activated
by a water-soluble carbodiimide. The most favorable carbodiimide wasN-cyclohexyl-Nt’-(methyl-2-p-nitrophenyl-2-oxoethyl) aminopropyl carbodiimide methyl bromide, but for practical purposes,N-cyclohexyl-Nt’-morpholinoethyl carbodiimide methyl tosylate was used. The optimal conditions for the coupling procedure were
determined. The catalytic activity of the immobilized arginase was 290–340 U/g solid or 2.9–3.4 U/mL wet gel. The pH optimum
for the catalytic activity was pH 9.5, the apparent temperature maximum was at 60°C and Kmapp was calculated to be 0.37M L-arginine. Immobilization markedly improved the conformational stability of arginase. At 60°C,
the pH for maximal stability was found to be 8.0. The immobilized arginase was used for the production of L-ornithine and
D-arginine. 相似文献
74.
Interactions of water and methanol with a mixture of copper and zinc metals: a theoretical <Emphasis Type="Italic">ab initio</Emphasis> study 总被引:1,自引:0,他引:1
Ab initio cluster quantum chemical calculations at the Hartree–Fock and second-order Møller–Plesset perturbation theory levels were carried out to mimic the interactions of water and methanol with a mixture of Cu and Zn metals. It was shown that both molecular and dissociative adsorption of methanol on a mixture of Cu and Zn metal catalyst are preferred over the corresponding adsorptions of water. Estimated transition-state structures for dissociation of methanol into CH·3 and OH· lie about 9.0 and 22.0 kcal/mol higher compared to the dissociated (forward reaction) and molecular adsorption (reverse reaction) complexes, respectively. Based on distinct radicals' bond energies with the active sites of the catalyst considered, it is suggested that hydrogen molecules could be formed through a chain of homogeneous reactions of methyl radicals released into the gas phase with the water and/or methanol molecules. 相似文献
75.
Shengbao Diao Mei Jin Jinfeng Sun Yi Zhou Chao Ye Yong Jin 《Natural product research》2019,33(5):701-707
A new diarylheptanoid, (2S,3S,5S)-2,3,5-trihydroxy-1,7-bis(4-hydroxy- 3-methoxyphenyl)heptane (1), and a new diarylheptanoid glycoside, (2S,3S,5S)-2,3-dihydroxy-5-O-β-d-xylopyranosyl-7-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)heptane (2), together with three known compounds, rhoiptelol C (3), rhoiptelol B (4) and 3′,4″-epoxy-2-O-β-d-glucopyanosyl-1-(4-hydroxyphenyl)- 7-(3-methoxyphenyl)heptan-3-one (5) were isolated from the roots of Juglans mandshurica (Juglandaceae). The structures of compounds 1 and 2 were identified based on HR-ESI-MS, 1D and 2D NMR spectroscopic methods. Compounds 1–5 were assayed for their inhibitory effects on the production of NO, TNF-α and IL-6 in LPS-stimulated RAW264.7 cells. 相似文献
76.
Peter Brodelius Kjell Nilsson Klaus Mosbach 《Applied biochemistry and biotechnology》1981,6(4):293-307
Whole cells ofTrigonopsis variabilis were immobilized by entrapment in Ca2+-alginate and used for the production of α-keto acids from the corresponding D-amino acids. The D-amino acid oxidase within
the immobilized cells has a broad substrate specificity. Hydrogen peroxide formed in the enzymatic reaction was efficiently
hydrolyzed by manganese oxide co-immobilized with the cells. The amino acid oxidase activity was assayed with a new method
based on reversed-phase HPLC. Oxygen requirements, bead size, concentration of cells in the beads, flow rate, and other factors
were investigated in a “ trickle-bed ” reactor. 相似文献
77.
Summary. Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about
a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the
order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent
to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small
excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging
to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition
curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given. 相似文献
78.
79.
Glucose utilization by lysine-producing fluoroacetate-sensitive mutants ofCorynebacterium glutamicum
A fluoroacetate-sensitive mutant was isolated fromCorynebacterium glutamicum, ATCC 21513, following mutagenesis with NTG. Batch fermentations show that in terms of growth kinetics, glucose utilization,
and lysine formation, there are significant differences between the mutant and the parent. The mutant’s specific growth rate
(0.22/h) is lower than that for the parent (0.34/h). Also, the yield expressed as lysine/glucose consumed does not alter as
a function of the glucose concentration for the mutant, and is about 0.22, whereas for the parent, this coefficient decreases
with increasing glucose concentration. The maximum specific rate of lysine production for the mutant is 1.3 g/L/h that is
about two-fold higher than that for the parent. 相似文献
80.
Citric acid is finding new areas of use each year and the demand for the acid is constantly increasing. Being a bulk chemical,
the continuous production of citric acid would be advantageous. The paper presents the results from ammonia limited batch
and continuous fermentations using the yeast strainSaccharomycopsis (Candida) lipolytica (NRRL Y-7576). Mathematical models were developed for growth and glucose utilization in batch and continuous culture. Cell
and acid yields appeared to be almost the same in batch and continuous culture. The specific production rates were found to
be constant, equal to 0.053 g/g h, in the batch fermentations but varied in the continuous experiments from 0 to 0.11 g/g
h depending on the fermentation conditions. Continuous production in a single stage CSTR was studied for over 1,000 hours
without shutdown. 相似文献