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144.
Marit Valeur Ramstad Trond E. Ellingsen Kjell D. Josefsen Hilde K. Hidal
Svein Valla
Gudmund Skjk-Brk David W. Levine 《Enzyme and microbial technology》1999,24(10):23819-646
The mannuronan C-5-epimerase AlgE2 is one of a family of Ca2+-dependent epimerases secreted by Azotobacter vinelandii. These enzymes catalyze the conversion of β-
-mannuronic acid residues (M) to -
-guluronic acid residues (G) in alginate. AlgE2 has been produced by fermentation with a recombinant strain of Escherichia coli, isolated and partially purified. Epimerization with AlgE2 increased the content of G-residues in different alginates from starting values of 0–45% up to approximately 70%. The new G-residues were mainly present in short blocks. Although G-residues may be introduced next to pre-existing G-residues, AlgE2 was not able to epimerize strictly alternating MG-structures. The epimerization with AlgE2 was greatly affected by the concentration of Ca2+. The type of alginate used as substrate affected the reaction rate and the reaction pattern especially at low Ca2+ concentration. AlgE2 appears to act by a preferred attack mechanism where the enzyme associates with different sequences in the alginate depending on the concentration of Ca2+. During epimerization, AlgE2 occasionally causes cleavage of the alginate chain. The observed frequency corresponds to 1–3 breaks per 1,000 M-units epimerized. 相似文献
145.
Catrin Furster Kjell Wikvall 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》1999,1437(1):46-52
Human liver microsomes catalyze an efficient 25-hydroxylation of 5β-cholestane-3α,7α,12α-triol. The hydroxylation is involved in a minor, alternative pathway for side-chain degradation in the biosynthesis of cholic acid. The enzyme responsible for the microsomal 25-hydroxylation has been unidentified. In the present study, recombinant expressed human P-450 enzymes have been used to screen for 25-hydroxylase activity towards 5β-cholestane-3α,7α,12α-triol. High activity was found with CYP3A4, but also with CYP3A5 and to a minor extent with CYP2C19 and CYP2B6. Small amounts of 23- and 24-hydroxylated products were also formed by CYP3A4. The Vmax for 25-hydroxylation by CYP3A4 and CYP3A5 was 16 and 4.5 nmol/(nmol×min), respectively. The Km was 6 μM for CYP3A4 and 32 μM for CYP3A5. Cytochrome b5 increased the hydroxylase activities. Human liver microsomes from ten different donors, in which different P-450 marker activities had been determined, were incubated with 5β-cholestane-3α,7α,12α-triol. A strong correlation was observed between formation of 25-hydroxylated 5β-cholestane-3α,7α,12α-triol and CYP3A levels (r2=0.96). No correlation was observed with the levels of CYP2C19. Troleandomycin, a specific inhibitor of CYP3A4 and 3A5, inhibited the 25-hydroxylase activity of pooled human liver microsomes by more than 90% at 50 μM. Tranylcypromine, an inhibitor of CYP2C19, had very little effect on the conversion. From these results, it can be concluded that CYP3A4 is the predominant enzyme responsible for 25-hydroxylation of 5β-cholestane-3α,7α,12α-triol in human liver microsomes. 相似文献
146.
Peter Stlberg Shu Wang Catharina Larsson Günther Weber Kjell
berg Anders Gobl Britt Skogseid 《FEBS letters》1999,450(3):703
The expression of phospholipase C β 3 (PLCB3) is low or absent in several neuroendocrine neoplasias. To investigate the role of PLCB3 in the neuroendocrine tumorigenesis, we transfected a PLCB3 construct to three neuroendocrine tumor cell lines with a low PLCB3 expression. The growth rate and tumorigenicity were assessed in vitro by [3H]thymidine incorporation and cell counting, in vivo, by xenografting to nude mice. In vitro, PLCB3 expressing clones showed a significant growth inhibition. The tumor weight was reduced for one of the two xenografted PLCB3-transfected cell lines and in both, a reduced number of proliferating (Ki-67 positive) cells was observed. This study implies an essential role for PLCB3 in the neuroendocrine tumorigenesis. 相似文献
147.
Digital cellular telephones using the GSM (Global System for Mobile Communication) transmit information in bursts of microwaves. This pulsed transmitting mode causes the battery current and currents in the electronics of the apparatus to be pulsed. These pulsed currents produce corresponding pulsed magnetic fields near the phones. A study to determine the magnitude of these fields involved two models of digital telephones. The highest value of the magnetic flux density was 1.8 μT (rms). Bioelectromagnetics 18:184–186, 1997. © 1997 Wiley-Liss, Inc. 相似文献
148.
149.
Karl A Franklin Christer Janson Thórarinn Gíslason Amund Gulsvik Maria Gunnbj?rnsdottir Birger N Laerum Eva Lindberg Eva Norrman Lennarth Nystr?m Ernst Omenaas Kjell Torén Cecilie Svanes 《Respiratory research》2008,9(1):63
Background
To our knowledge, no studies of the possible association of early life environment with snoring in adulthood have been published. We aimed to investigate whether early life environment is associated with snoring later in life.Methods
A questionnaire including snoring frequency in adulthood and environmental factors in early life was obtained from 16,190 randomly selected men and women, aged 25–54 years, in Sweden, Norway, Iceland, Denmark and Estonia (response rate 74%).Results
A total of 15,556 subjects answered the questions on snoring. Habitual snoring, defined as loud and disturbing snoring at least 3 nights a week, was reported by 18%. Being hospitalized for a respiratory infection before the age of two years (adjusted odds ratio (OR) = 1.27; 95% confidence interval (CI) 1.01–1.59), suffering from recurrent otitis as a child (OR = 1.18; 95%CI 1.05–1.33), growing up in a large family (OR = 1.04; 95%CI 1.002–1.07) and being exposed to a dog at home as a newborn (OR = 1.26; 95%CI 1.12–1.42) were independently related to snoring later in life and independent of a number of possible confounders in adulthood. The same childhood environmental factors except household size were also related with snoring and daytime sleepiness combined.Conclusion
The predisposition for adult snoring may be partly established early in life. Having had severe airway infections or recurrent otitis in childhood, being exposed to a dog as a newborn and growing up in a large family are environmental factors associated with snoring in adulthood. 相似文献150.
Maribasappa Karched Riikka Ihalin Kjell Eneslätt Deyu Zhong Jan Oscarsson Sun N Wai Casey Chen Sirkka E Asikainen 《BMC microbiology》2008,8(1):18