| 1. |
- Hansson, Mattias, et al.
(författare)
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Artifactual insulin release from differentiated embryonic stem cells.
- 2004
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Ingår i: Diabetes. - 0012-1797. ; 53:10, s. 2603-9
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Tidskriftsartikel (refereegranskat)abstract
- Several recent reports claim the generation of insulin-producing cells from embryonic stem cells via the differentiation of progenitors that express nestin. Here, we investigate further the properties of these insulin-containing cells. We find that although differentiated cells contain immunoreactive insulin, they do not contain proinsulin-derived C-peptide. Furthermore, we find variable insulin release from these cells upon glucose addition, but C-peptide release is never detected. In addition, many of the insulin-immunoreactive cells are undergoing apoptosis or necrosis. We further show that cells cultured in the presence of a phosphoinositide 3-kinase inhibitor, which previously was reported to facilitate the differentiation of insulin(+) cells, are not C-peptide immunoreactive but take up fluorescein isothiocyanate-labeled insulin from the culture medium. Together, these data suggest that nestin(+) progenitor cells give rise to a population of cells that contain insulin, not as a result of biosynthesis but from the uptake of exogenous insulin. We conclude that C-peptide biosynthesis and secretion should be demonstrated to claim insulin production from embryonic stem cell progeny.
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| 2. |
- Jansson, Hanna, 1975, et al.
(författare)
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The crystal structure of the spinach plastocyanin double mutant G8D/L12E gives insight into its low reactivity towards photosystem 1 and cytochrome f
- 2003
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1607:2-3, s. 203-210
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Tidskriftsartikel (refereegranskat)abstract
- Plastocyanin (Pc) is a copper-containing protein, which functions as an electron carrier between the cytochrome b6f and photosystem 1 (PS1) complexes in the photosynthetic electron transfer (ET) chain. The ET is mediated by His87 situated in the hydrophobic surface in the north region of Pc. Also situated in this region is Leu12, which mutated to other amino acids severely disturbs the ET from cytochrome f and to PS1, indicating the importance of the hydrophobic surface. The crystal structure of the Pc double mutant G8D/L12E has been determined to 2.0 Å resolution, with a crystallographic R-factor of 18.3% (Rfree=23.2%). A comparison with the wild-type structure reveals that structural differences are limited to the sites of the mutations. In particular, there is a small but significant change in the hydrophobic surface close to His87. Evidently, this leads to a mismatch in the reactive complex with the redox partners. For PS1 this results in a 20 times weaker binding and an eightfold slower ET as determined by kinetic measurements. The mutations that have been introduced do not affect the optical absorption spectrum. However, there is a small change in the EPR spectrum, which can be related to changes in the copper coordination geometry.
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