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191.
Urea hydrolysis by immobilized urease in a fixed-bed reactor: analysis and kinetic parameter estimation 总被引:2,自引:0,他引:2
Urea hydrolysis by urease immobilized onto ion exchange resins in a fixed-bed reactor has been studied. A modified Michaelis-Menten rate expression is used to describe the pH-dependent, substrate- and product-inhibited kinetics. Ionic equilibria of product and buffer species are included to account for pH changes generated by reaction. An isothermal, heterogeneous plug-flow reactor model has been developed. An effectiveness factor is used to describe the reaction-diffusion process within the particle phase. The procedure for covalent immobilization of urease onto macroporous cation exchangers is described. Urea conversion data are used to estimate kinetic parameters by a simplex optimization method. The best-fitted parameters are then used to predict the outlet conversions and pH values for systems with various inlet pH values, inlet urea and ammonia concentrations, buffers, particle sizes, and spacetimes. Very good agreement is obtained between experimental data and model predictions. This immobilized urease system exhibits quite different kinetic behavior from soluble urease because the pH near the enzyme active sites is different from that of the pore fluid. This effect results in a shift of the optimal pH value of the V(max) (pH) curve from 6.6 (soluble urease) to ca. 7.6 in dialysate solution, and ca. pH 8.0 in 20mM phosphate buffer. The reactor model is especially useful for estimating intrinsic kinetic parameters of immobilized enzymes and for designing urea removal columns. 相似文献
192.
Growth and death in overagitated microcarrier cell cultures 总被引:1,自引:0,他引:1
The effects of hydrodynamic forces on cell growth are investigated for animal cells growing on microcarriers. A reduction in net growth was observed with high levels of agitation. DNA measurements indicated that the reduction in net growth was due entirely to cell death, from hydrodynamic forces. No inhibition or enhancement of cell replication appeared to occur with high levels of agitation. 相似文献
193.
Stimulation of progesterone and prostaglandin E2 production by lipoxygenase metabolites of arachidonic acid 总被引:1,自引:0,他引:1
The role of several lipoxygenase metabolites of arachidonic acid in the action of luteinizing hormone-releasing hormone (LHRH) on ovarian hormone production was investigated. Like LHRH, treatment of rat granulosa cells with 5-HETE, 5-HPETE, 12-HETE, 15-HETE or 15-HPETE stimulated progesterone (P) and prostaglandin E2 (PGE2) production. 12-HEPE was most potent and stimulated P and PGE2 equally well. By contrast, 5-HETE stimulated P better than PGE2, while 15-HETE was a potent stimulator of PGE2 but not of P. Stimulation of P and PGE2 by LHRH or 12-O-tetradecanoylphorbol 13-acetate (TPA) was further augmented by several HETEs and HPETEs. Like protein kinase C, arachidonic acid metabolites appear to mediate the multiple actions of LHRH in the ovary. 相似文献
194.
Molecular genetics of phenylketonuria in Orientals: linkage disequilibrium between a termination mutation and haplotype 4 of the phenylalanine hydroxylase gene. 总被引:11,自引:8,他引:3 下载免费PDF全文
T Wang Y Okano R Eisensmith S Z Huang Y T Zeng W H Lo S L Woo 《American journal of human genetics》1989,45(5):675-680
Phenylketonuria (PKU) is a common metabolic disorder among Chinese, with a prevalence of about 1 in 16,500 births. This frequency is very similar to that among Caucasians. Individual exons of the phenylalanine hydroxylase (PAH) gene with flanking introns were amplified by polymerase chain reaction and cloned into M13 for sequence analysis. An Arg111-to-Ter111 mutation has been identified in exon 3 of the PAH gene in a Chinese PKU patient. The mutation is in linkage disequilibrium with the mutant haplotype 4 alleles which are the most prevalent haplotype among the Orientals. The mutation accounts for about 10% of the Chinese PKU alleles and is absent from the Caucasians, demonstrating that independent mutational events have occurred in the PAH locus after racial divergence. 相似文献
195.
In the present work we have explored conditions for using a pulsed amperometric detector for on-line analysis of oligosaccharides eluted from a high-performance liquid affinity chromatography column. A monoclonal antibody that specifically binds a glucose-containing oligosaccharide is coupled to a SelectiSphere-10-activated tresyl column. The system is eluted isocratically and easily detects 10 ng of the oligosaccharide with a linear response up to 250 ng. Analysis of both serum and urine samples from normal individuals and patients with acute pancreatitis gives a single retarded peak with a retention time identical to that of authentic (Glc)4. Retarded material pooled from several analyses of urine was positively identified as (Glc)4 by GC-MS analysis. As this method requires little cleanup and no chemical derivitization of the sample and is performed rapidly (less than 20 min) at sensitivities of at least 10 micrograms/liter in biological fluids, it represents a substantial improvement over previous GC-MS, radioimmunoassay, and enzyme-linked immunoadsorbent assay methods used to determine (Glc)4. 相似文献
196.
Isolation and Characterization of an Enterobacter cloacae Strain That Reduces Hexavalent Chromium under Anaerobic Conditions 总被引:12,自引:6,他引:6 下载免费PDF全文
Pi-Chao Wang Tsukasa Mori Kohya Komori Masanori Sasatsu Kiyoshi Toda Hisao Ohtake 《Applied microbiology》1989,55(7):1665-1669
An Enterobacter cloacae strain (HO1) capable of reducing hexavalent chromium (chromate) was isolated from activated sludge. This bacterium was resistant to chromate under both aerobic and anaerobic conditions. Only the anaerobic culture of the E. cloacae isolate showed chromate reduction. In the anaerobic culture, yellow turned white with chromate and the turbidity increased as the reduction proceeded, suggesting that insoluble chromium hydroxide was formed. E. cloacae is likely to utilize toxic chromate as an electron acceptor anaerobically because (i) the anaerobic growth of E. cloacae HO1 accompanied the decrease of toxic chromate in culture medium, (ii) the chromate-reducing activity was rapidly inhibited by oxygen, and (iii) the reduction occurred more rapidly in glycerol- or acetate-grown cells than in glucose-grown cells. The chromate reduction in E. cloacae HO1 was observed at pH 6.0 to 8.5 (optimum pH, 7.0) and at 10 to 40°C (optimum, 30°C). 相似文献
197.
X Wang N Sato M A Greer S E Greer S McAdams 《Biochemical and biophysical research communications》1989,163(1):471-475
The permeant molecules, urea and glycerol, evoked a prompt secretory burst of TSH and PRL when added to the extracellular medium of acutely dispersed anterior pituitary cells. Secretion of both hormones was proportional to the concentration of urea or glycerol between 26 and 104 mM (r greater than 0.89, P less than 0.001). Equivalent concentrations of the impermeant molecule, mannitol, did not induce secretion. The acute TSH and PRL secretory responses to TRH, hyposmolarity, and permeant molecules were qualitatively indistinguishable. These data support our hypothesis that cell swelling and resultant plasmalemma expansion is a potent inducer of hormone secretion. Since the secretory response to permeant molecules was not reduced in a Ca2+-free medium containing 0.1 mM EGTA, an increase in Ca2+ transport across the plasmalemma to raise cytosol Ca2+ concentration does not appear involved. 相似文献
198.
Tyrosine phosphorylation in human neutrophil 总被引:9,自引:0,他引:9
J Gomez-Cambronero C K Huang V A Bonak E Wang J E Casnellie T Shiraishi R I Sha'afi 《Biochemical and biophysical research communications》1989,162(3):1478-1485
Protein tyrosine phosphorylation in human neutrophils was examined by immunoblotting with antibodies specific for phosphotyrosine. The addition of the human hormone granulocyte-macrophage colony stimulating factor to human neutrophils caused an increase in the tyrosine phosphorylation levels of several proteins. The increases in at least two of these proteins having molecular masses of 40 kDa (p40) and 54 kDa (p54) were rapid and were inhibited in pertussis toxin treated cells. The newly synthesized tyrosine kinase inhibitor ST 638 inhibited the increases in the levels of the tyrosine phosphorylation in p92, p78, p54 and p40 proteins. The epidermal growth factor receptor tyrosine kinase inhibitors were less effective. The addition of the chemotactic factor fMet-Leu-Phe to human neutrophils also caused an increase in tyrosine phosphorylation in some of these proteins. The pattern of the fMet-Leu-Phe-induced tyrosine phosphorylation was different from that produced by GM-CSF. The increases were also inhibited by ST 638. In addition, ST 638 inhibited superoxide production but not actin polymerization in control and GM-CSF-treated cells stimulated with fMet-Leu-Phe. Moreover, the active but not inactive phorbol esters increase the tyrosine phosphorylation only in the 40 kDa protein. These results suggest several points: (a) some of the responses produced by GM-CSF and fMet-Leu-Phe are mediated through tyrosine phosphorylation, (b) the GM-CSF receptor is coupled to a pertussis toxin sensitive G-protein, (c) the 40 kDa protein is probably the Gi alpha 2, and (d) the 78 or the 92 kDa protein is most likely the receptor for GM-CSF, which indicates that the receptor may have a tyrosine kinase domain. 相似文献
199.
L F Wang R H Doi L F Chuang B I Osburn J Maisonnave E Benjamini R Y Chuang 《Biochemical and biophysical research communications》1989,162(2):892-899
The cDNA coding for the major nonstructural protein, NS1, of bluetongue serotype 17 (BTV-17) was cloned previously. Using pUC plasmids, we have successfully expressed the NS1 protein in Escherichia coli as a LacZ-NS1 fusion protein. The recombinant NS1 protein reacted with rabbit anti-BTV-17 antiserum, and was thus immunologically indistinguishable from the native BTV-17 NS1 protein. This was the first bluetongue viral protein to be produced in a bacterial system. 相似文献
200.
We have previously shown that pH-sensitive immunoliposomes can mediate a target-specific delivery of plasmid DNA to tumor cells grown in a mouse model [Wang, C.-Y., & Huang, L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7851-7855]. The efficiency of delivery in terms of the target cell transformation frequency has now been characterized for both short- and long-term gene expression in a tissue culture system. Herpes simplex virus thymidine kinase (TK) gene was used as a reporter gene. It was placed under the control of the promoter for the rat phosphoenolpyruvate carboxykinase gene, which contains a cAMP regulatory element. Therefore, the expression of the exogenous gene in the target cell, mouse Ltk- cells, can be regulated by cAMP drugs. The plasmid DNA was encapsulated in liposomes using a detergent dialysis method. The efficiency of gene delivery was optimized with respect to the time course and dose of liposome-associated DNA. The existence of antibody of the liposomes was essential for the maximal level of DNA delivery. Delivery was also dependent on the lipid composition of the liposome. The pH-sensitive lipid composition gave 8-fold higher efficiency than the corresponding pH-insensitive composition. The transformation efficiency of the target cell also depended on the regulation of gene expression; cells incubated with dibutyryl-cAMP and theophylline showed a much higher level of transformation frequency than cells incubated without the drugs. When all liposome and incubation parameters are optimized, the Ltk- cells showed a 47% efficiency for the short-term transformation, and 2% for the long-term transformation.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献