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| 2. |
- Börner, Tim, et al.
(författare)
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Explaining Operational Instability of Amine Transaminases : Substrate-Induced Inactivation Mechanism and Influence of Quaternary Structure on Enzyme-Cofactor Intermediate Stability
- 2017
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:2, s. 1259-1269
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Tidskriftsartikel (refereegranskat)abstract
- The insufficient operational stability of amine transaminases (ATA) constitutes a limiting factor for high productivity in chiral amine synthesis. In this work, we investigated the operational stability of a tetrameric ATA with 92% sequence identity to a Pseudomonas sp. transaminase and compared it to the two commonly used dimeric ATAs from Chromobacterium violaceum and Vibrio fluvialis. In the presence of substrate, all three ATAs featured reduced stability in comparison to their resting stability, but the tetramer showed slower inactivation rates than the dimeric ATAs. Kinetic and thermodynamic analysis revealed an amine donor induced inactivation mechanism involving accumulation of the less stable aminated enzyme-cofactor intermediate. Dissociation of the enzyme-PMP complex forms the unstable apoenzyme, which can rapidly unfold. Crystal structure analysis shed light on the structure-function relationship suggesting that the cofactor-ring binding element is stabilized in the quaternary structure conferring higher operational stability by minimizing PMP leakage and apoenzyme formation. In contrast to the common practice, increasing the amine acceptor content improved the stability and substrate turnover of dimeric ATAs. An extra supply of the pyridoxal cofactor (PLP) enhanced the stability of dimeric and tetrameric ATAs but reduced the transamination activity. The ATA inactivation mechanism described here provides valuable aspects for both process development and protein engineering.
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| 3. |
- Fridner, Ann, et al.
(författare)
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Recent suicidal ideation among female and male university hospital physicians in Sweden (The HOUPE Study) : Associations with work stressors
- 2008
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Ingår i: 3rd International Congress of Gender Medicine, Stockholm, Sweden, the 12-14th of September 2008.
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Konferensbidrag (refereegranskat)abstract
- Background: Suicide rates for physicians are noted to be higher than for the general population, mainly related to high rates among female physicians. Female physicians have been reported to admit to significantly more suicidal thoughts than male physicians. Suicide ideation is a recognized precursor of suicide. The urgent need to examine the reasons for suicide risk among female physicians is underscored by society’s increasing dependence upon this group of health providers. Suicide impacts not only upon the physician’s personal circle, but upon the colleagues, staff and patients alike. We examine the relationship between work stressors and recent suicide ideation among male and female physicians in Sweden.Methods: Cross-sectional questionnaire-based study including the General Nordic Questionnaire for Psychological and Social Factors at Work (QPS-Nordic), Physician Career Path Questionnaire (PCPQ) and the Mehan Suicidal Ideation Scale. The questionnaire was completed by physicians working at the Karolinska University Hospital, Stockholm. Multiple logistic regression was used to identify sets of independent variables showing the strongest association with suicidal ideation within the last 12 months.Results: Altogether 50 of the 385 Swedish female physicians and 42 of the 434 male physicians reported having suicidal thoughts within the last 12 months. Among the female physicians, adjusting for non-significant covariates: age, having a partner and number of children, the two work-related variables associated with suicidal ideation within the last 12 months were: having been subjected to degrading experiences at work (Odds Ratio (OR)=3.11, 95% Confidence Interval (CI) =1.52–6.38) and not having regular meetings to discuss stressful situations at work (OR=2.82, CI=1.04–7.63). Self diagnosis and treatment was also significantly associated with recent suicidal ideation. The same covariates were included for the male physicians, for whom having been subjected to degrading experiences at work was significant (OR=4.25, CI=1.60-11.25).Conclusions: Albeit statistically non-significant, more than the expected number of female physicians compared to males had recent suicidal ideation. Recent suicidal ideation among both male and female physicians in Sweden showed a strong association with an important work stressor: having been subjected to degrading experiences at work. For Swedish female physicians, having meetings to discuss work stressors may be protective.
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| 4. |
- Gulshan Kazi, Zubaida, et al.
(författare)
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A CGTase with high coupling activity using γ-cyclodextrin isolated from a novel strain clustering under the genus Carboxydocella.
- 2015
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 1460-2423 .- 0959-6658. ; 25:5, s. 514-523
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Tidskriftsartikel (refereegranskat)abstract
- Cyclodextrin glucanotransferases (CGTases; EC 2.4.1.19) have mainly been characterized for their ability to produce cyclodextrins (CDs) from starch in an intramolecular transglycosylation reaction (cyclization). However, this class of enzymes can also catalyze intermolecular transglycosylation via disproportionation or coupling reactions onto a wide array of acceptors and could therefore be valuable as a tool for glycosylation. In this paper, we report the gene isolation, via the CODEHOP-strategy, expression and characterization of a novel CGTase (CspCGT13) from a Carboxydocella sp. This enzyme is the first glycoside hydrolase isolated from the genus, indicating starch degradation via cyclodextrin production in the Carboxydocella strain. The fundamental reactivities of this novel CGTase are characterized and compared to two commercial CGTases, assayed under identical condition, in order to facilitate interpretation of the results. The comparison showed that the enzyme, CspCGT13, displayed high coupling activity using γ-CD as donor, despite preferentially forming α and β-CD in the cyclization reaction using wheat starch as substrate. Comparison of subsite conservation within previously characterized CGTases showed significant sequence variation in subsite -3 and -7, which may be important for the coupling activity.
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| 5. |
- Hallmans, Göran, et al.
(författare)
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Rye, lignans and human health
- 2003
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Ingår i: Proceedings of the Nutrition Society. - 0029-6651 .- 1475-2719. ; 62:1, s. 193-9
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Tidskriftsartikel (refereegranskat)abstract
- Rye bran contains a high content not only of dietary fibre, but also of plant lignans and other bioactive compounds in the so-called dietary fibre complex. Blood concentrations of lignans such as enterolactone have been used as biomarkers of intake of lignan-rich plant food. At present,evidence from studies in human subjects does not warrant the conclusion that rye, whole grains orphyto-oestrogens protect against cancer. Some studies, however, have pointed in that direction,especially in relation to cancers of the upper digestive tract. A number of prospective epidemiological studies have clearly shown a protective effect of wholegrain cereals against myocardial infarctions. A corresponding protective effect against diabetes and ischaemic stroke(brain infarct) has also been demonstrated. It seems reasonable to assume that these protective effects are associated with one or more factors in the dietary fibre complex.
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| 6. |
- Heintz, Søren, et al.
(författare)
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Development of in situ product removal strategies in biocatalysis applying scaled-down unit operations
- 2017
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592. ; 114:3, s. 600-609
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Tidskriftsartikel (refereegranskat)abstract
- An experimental platform based on scaled-down unit operations combined in a plug-and-play manner enables easy and highly flexible testing of advanced biocatalytic process options such as in situ product removal (ISPR) process strategies. In such a platform, it is possible to compartmentalize different process steps while operating it as a combined system, giving the possibility to test and characterize the performance of novel process concepts and biocatalysts with minimal influence of inhibitory products. Here the capabilities of performing process development by applying scaled-down unit operations are highlighted through a case study investigating the asymmetric synthesis of 1-methyl-3-phenylpropylamine (MPPA) using ω-transaminase, an enzyme in the sub-family of amino transferases (ATAs). An on-line HPLC system was applied to avoid manual sample handling and to semi-automatically characterize ω-transaminases in a scaled-down packed-bed reactor (PBR) module, showing MPPA as a strong inhibitor. To overcome the inhibition, a two-step liquid–liquid extraction (LLE) ISPR concept was tested using scaled-down unit operations combined in a plug-and-play manner. Through the tested ISPR concept, it was possible to continuously feed the main substrate benzylacetone (BA) and extract the main product MPPA throughout the reaction, thereby overcoming the challenges of low substrate solubility and product inhibition. The tested ISPR concept achieved a product concentration of 26.5 gMPPA · L−1, a purity up to 70% gMPPA · gtot −1 and a recovery in the range of 80% mol · mol−1 of MPPA in 20 h, with the possibility to increase the concentration, purity, and recovery further. Biotechnol. Bioeng. 2017;114: 600–609.
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| 9. |
- Pinheiro, H. M., et al.
(författare)
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Quinones as external electron acceptors in steroid dehydrogenation with entrapped cells in organic medium
- 1993
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422. ; 7:2, s. 83-96
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Tidskriftsartikel (refereegranskat)abstract
- A series of quinone-based compounds were tested for their ability to act as external electron acceptors in the 1-dehydrogenation of-αmethyl-hydrocortisone-21-acetate, with polyurethane-entrapped Arthrobacter simplex cells in buffer-saturated n-decan-1-ol. This organic solvent was needed to solubilize the steroid substrate. In aqueous medium, the conversion with free cells virtually stopped after one hour, probably due to substrate limitation. All the tested quinones acted as external electron acceptors, increasing the bioconversion rate. The process kinetics were complex. However, when keeping the concentration of one of the substrates (steroid or quinone) constant and varying that of the other, Michaelis-Menten kinetics provided a reasonably good model for the initial reaction rates, and apparent kinetic constants were estimated. The most effective of the tested external electron acceptors were 2,6-dimethyl-p-benzoquinone and menadione. Mass transfer limitations seemed to appear after some hours of reaction, with low concentrations of the more efficient quinones, when the biocatalyst microenvironment was quinone- and possibly oxygen-depleted. Monosodium glutamate was included with the cells in the immobilisation foam, as an activity-stabilizing agent. It was observed that some of the quinones apparently formed complexes with this glutamate, thereby influencing the kinetics of the process. The catalytic half-life of the system depended on the quinone concentration and optimal values (60-80 h) were observed at 1 mM levels of 2,6-dimethyl-p-benzoquinone or menadione. Quinone toxicity, direct or through the formation of peroxides in the aerobic reoxidation process, may be at the origin of enzyme deactivation.
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| 10. |
- Sonestedt, Emily, et al.
(författare)
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Variation in fasting and non-fasting serum enterolactone concentrations in women of the Malmo Diet and Cancer cohort
- 2008
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Ingår i: European Journal of Clinical Nutrition. - : Springer Science and Business Media LLC. - 1476-5640 .- 0954-3007. ; 62:8, s. 1005-1009
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Tidskriftsartikel (refereegranskat)abstract
- Objectives:The aim of this study was to examine the variation of enterolactone from fasting and non-fasting blood of middle-aged healthy women eating a normal diet to determine the usefulness of a single sample in epidemiological studies.Subjects and methods:Twenty-six women born between 1940 and 1950 were recruited within the Malmo Diet and Cancer cohort. Three non-fasting and two overnight fasting samples were collected from each individual during a 5-week period. Twenty-one participated in all measurements. Enterolactone concentrations were analyzed by time-resolved fluoroimmunoassay.Results:The within-subject and between-subject variations (coefficient of variations, CV) were estimated to 59 and 89% respectively for fasting samples and 71 and 67% for non-fasting samples. The intraclass correlation coefficients (ICC) were estimated to 0.66 (95% confidence interval (CI) 0.35-0.84) for fasting and 0.48 (95% CI, 0.22-0.72) for non-fasting samples.Conclusions:Although the estimated ICC for blood samples was moderate, it indicates that enterolactone levels of both fasting and non-fasting blood samples should be useful in future projects within the Malmo Diet and Cancer cohort.European Journal of Clinical Nutrition advance online publication, 30 May 2007; doi:10.1038/sj.ejcn.1602811.
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