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41.
A microbial protease was immobilized by covalent attachment, to porous glass. This material was characterized for pH optimum, thermal stability, and operational half–life using casein as substrate. The immobilized enzyme was used for preparation of soya hydrolysates, low in free amino acids with high solubility. 相似文献
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Alton G; Hasilik M; Niehues R; Panneerselvam K; Etchison JR; Fana F; Freeze HH 《Glycobiology》1998,8(3):285-295
Direct utilization of mannose for glycoprotein biosynthesis has not been
studied because cellular mannose is assumed to be derived entirely from
glucose. However, animal sera contain sufficient mannose to force uptake
through glucose-tolerant, mannose-specific transporters. Under
physiological conditions this transport system provides 75% of the mannose
for protein glycosylation in human hepatoma cells despite a 50- to 100-fold
higher concentration of glucose. This suggests that direct use of mannose
is more important than conversion from glucose. Consistent with this
finding the liver is low in phosphomannose isomerase activity
(fructose-6-P<->mannose-6-P), the key enzyme for supplying
glucose-derived mannose to the N-glycosylation pathway. [2- 3H] Mannose is
rapidly absorbed from the intestine of anesthetized rats and cleared from
the blood with a t1/2of 30 min. After a 30 min lag, label is incorporated
into plasma glycoproteins, and into glycoproteins of all organs during the
first hour. Most (87%) of the initial incorporation occurs in the liver,
but this decreases as radiolabeled plasma glycoproteins increase.
Radiolabel in glycoproteins also increases 2- to 6-fold in other organs
between 1-8 h, especially in lung, skeletal muscle, and heart. These organs
may take up hepatic- derived radiolabeled plasma glycoproteins.
Significantly, the brain, which is not exposed to plasma glycoproteins,
shows essentially no increase in radiolabel. These results suggest that
mammals use mannose transporters to deliver mannose from blood to the liver
and other organs for glycoprotein biosynthesis. Additionally, contrary to
expectations, most of the mannose for glycoprotein biosynthesis in cultured
hepatoma cells is derived from mannose, not glucose. Extracellular mannose
may also make a significant contribution to glycoprotein biosynthesis in
the intact organism.
相似文献
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Trypsin was covalently immobilized on porous glass in the presence and absence of a specific substrate and reacted in various organic solvents of different dielectric constants. Optimum solvent concentration, pH profile, Km(app), Vmax(app), productivity versus temperature, activity, and reaction rates were determined. Reaction rates of six lysyl dipeptides were compared. Crystalline trypsin was dansylated for studies by nanosecond fluorescence techniques to determine the effects of introducing high concentrations of organic solvents on the molecule. The results indicated that greater reaction rates were observed with dipeptides having more acidic carboxyl terminal groups. The data also indicated that greater reaction rates were observed in higher concentrations of solvents of lower dielectric constants. Nanosecond fluorescence spectroscopy of trypsin in high concentrations of a low dielectric constant solvent indicated major dehydration even though maximal enzyme activity was achieved under these conditions. 相似文献
47.
The phylogeny and substitution rates of the mammalian X chromosome- located
and autosomal phosphoglycerate kinase and pyruvate dehydrogenase genes were
investigated. Compatibility analysis was used to show reticulate evolution
in these genes. Analysis of the marsupial, mouse, and human
phosphoglycerate kinase genes suggests that at least two recombination
events have taken place, one occurring about the time of the
placental-marsupial split involving exons 1-5 and the other before the
primate-rodent split involving exons 9-10. Similar analysis of the pyruvate
dehydrogenase genes indicates a recombination event involving exons 2-3 at
a time before the primate-rodent split and a gene conversion between exons
3-4 in the human somatic and testis- specific pyruvate dehydrogenase genes
after the primate-rodent split. This demonstrates that genetic exchange can
occur between paralogous genes at widely separated chromosomal locations.
Estimation of nucleotide substitution rates in these genes confirmed a
higher substitution rate in the pyruvate dehydrogenase genes. In the
phosphoglycerate kinase genes, there is no difference between the
substitution rates in mice and humans and between the X chromosome- and
autosome-located genes. A greater substitution rate was noted in the mouse
autosomal pyruvate dehydrogenase gene when compared with the other mouse
and human genes. This may be a result of either directional natural
selection or a relaxation of functional constraint at this specific gene.
相似文献
48.
Guangming Chen Hongyu Ren Anthony Turpoff Alexander Arefolov Richard Wilde James Takasugi Atiyya Khan Neil Almstead Zhengxian Gu Takashi Komatsu Connie Freund Jamie Breslin Joseph Colacino Jean Hedrick Marla Weetall Gary M. Karp 《Bioorganic & medicinal chemistry letters》2013,23(13):3942-3946
A series of novel 2-phenylindole analogs were synthesized and evaluated for activity in subgenomic HCV replicon inhibition assays. Several compounds containing small alkyl sulfonamides on the phenyl ring exhibiting submicromolar EC50 values against the genotype 1b replicon were identified. Among these, compound 25d potently inhibited the 1b replicon (EC50 = 0.17 μM) with 147-fold selectivity with respect to cytotoxicity. Compound 25d was stable in the presence of human liver microsomes and had a good pharmacokinetic profile in rats with an IV half-life of 4.3 h and oral bioavailability (F) of 58%. 相似文献
49.
Michael A. Arnold Aleksey I. Gerasyuto Jiashi Wang Wu Du Yi Jin Kim Gorske Tamil Arasu John Baird Neil G. Almstead Jana Narasimhan Srinivasa Peddi Olya Ginzburg Stanley W. Lue Jean Hedrick Josephine Sheedy Guy Lagaud Arthur A. Branstrom Marla Weetall J.V.N. Vara Prasad Gary M. Karp 《Bioorganic & medicinal chemistry letters》2017,27(22):5014-5021
The continued emergence of bacteria resistant to current standard of care antibiotics presents a rapidly growing threat to public health. New chemical entities (NCEs) to treat these serious infections are desperately needed. Herein we report the discovery, synthesis, SAR and in vivo efficacy of a novel series of 4-hydroxy-2-pyridones exhibiting activity against Gram-negative pathogens. Compound 1c, derived from the N-debenzylation of 1b, preferentially inhibits bacterial DNA synthesis as determined by standard macromolecular synthesis assays. The structural features of the 4-hydroxy-2-pyridone scaffold required for antibacterial activity were explored and compound 6q, identified through further optimization of the series, had an MIC90 value of 8?μg/mL against a panel of highly resistant strains of E. coli. In a murine septicemia model, compound 6q exhibited a PD50 of 8?mg/kg in mice infected with a lethal dose of E. coli. This novel series of 4-hydroxy-2-pyridones serves as an excellent starting point for the identification of NCEs treating Gram-negative infections. 相似文献
50.
Covalent bond between the enzyme amyloglucosidase and a porous glass carrier: The effect of shearing
H. H. Weetall N. B. Havewala H. M. Garfinkel W. M. Buehl G. Baum 《Biotechnology and bioengineering》1974,16(2):169-179
The utility of an immobilized enzyme depends not only on initial loading but also on operational half-life. The loss of activity of an immobilized enzyme in a column reactor may occur in several ways. It is therefore of interest to determine whether the decay in activity is due to the rupture of any of the enzyme-carrier bonds in the composite. In order to do this, it is first necessary to establish whether the enzyme on the composite is in fact covalently bound or adsorbed. In this report we have shown that there are a number of covalent links per protein molecule. We have also shown that the bond energies are sufficient to prevent shearing of the enzyme itself from the composite under any stresses which may occur in a chromatography column or packed-bed reactor during continuous operation. The effect of the siloxane linkage on composite stability is also discussed. 相似文献