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51.
Manikumar G Wadkins RM Bearss D Von Hoff DD Wani MC Wall ME 《Bioorganic & medicinal chemistry letters》2004,14(21):5377-5381
By developing a new synthetic procedure for introduction of side chains onto the camptothecin ring system, we were able to achieve the preparation of a number of analogs bearing bulky, hydrophobic groups directly attached to the 7-position. These include 7-tert-butylcamptothecin, 7-benzylcamptothecin and the corresponding 10,11-methylenedioxycamptothecins. This method involves the reaction of an appropriate orthoaminobenzonitrile with various Grignard reagents to give the corresponding orthoaminoketones. Friedlander condensation of the latter with the key tricyclic ketone leads to 7-substituted camptothecin analogs. We report the activity of these compounds as topoisomerase I poisons and their ability to inhibit growth of selected tumor cell lines. 相似文献
52.
Matysik J Schulten E Alia Gast P Raap J Lugtenburg J Hoff AJ de Groot HJ 《Biological chemistry》2001,382(8):1271-1276
Photochemically induced dynamic nuclear polarisation (photo-CIDNP) in intact bacterial reaction centres has been observed by 13C-solid state NMR under continuous illumination with white light. Strong intensity enhancement of 13C NMR signals of the aromatic rings allows probing the electronic ground state of the two BChl cofactors of the special pair at the molecular scale with atomic selectivity. Differences between the two BChl cofactors are discussed. Several aliphatic 13C atoms of cofactors, as well as 13C atoms of the imidazole ring of histidine residue(s), show nuclear-spin polarisation to the same extent as the aromatic nuclei of the cofactors. Mechanisms and applications of polarisation transfer are discussed. 相似文献
53.
54.
de Boer AL Neerken S de Wijn R Permentier HP Gast P Vijgenboom E Hoff AJ 《Photosynthesis research》2002,71(3):221-239
Mutants of Rhodobacter (Rba.) sphaeroides are described which were designed to study electron transfer along the so-called B-branch of reaction center (RC) cofactors.
Combining the mutation L(M214)H, which results in the incorporation of a bacteriochlorophyll, β, for HA [Kirmaier et al. (1991) Science 251: 922–927] with two mutations, G(M203)D and Y(M210)W, near BA, we have created a double and a triple mutant with long lifetimes of the excited state P* of the primary donor P, viz. 80 and 160 ps at room temperature, respectively. The yield of P+QA
− formation in these mutants is reduced to 50 and 30%, respectively, of that in wildtype RCs. For both mutants, the quantum
yield of P+HB
− formation was less than 10%, in contrast to the 15% B-branch electron transfer demonstrated in RCs of a similar mutant of
Rba. capsulatus with a P* lifetime of 15 ps [Heller et al. (1995) Science 269: 940–945]. We conclude that the lifetime of P* is not a governing factor in switching to B-branch electron transfer. The direct photoreduction of the secondary quinone,
QB, was studied with a triple mutant combining the G(M203)D, L(M214)H and A(M260)W mutations. In this triple mutant QA does not bind to the reaction center [Ridge et al. (1999) Photosynth Res 59: 9–26]. It is shown that B-branch electron transfer
leading to P+QB
− formation occurs to a minor extent at both room temperature and at cryogenic temperatures (about 3% following a saturating
laser flash at 20 K). In contrast, in wildtype RCs P+QB
− formation involves the A-branch and does not occur at all at cryogenic temperatures. Attempts to accumulate the P+QB
− state under continuous illumination were not successful. Charge recombination of P+QB
− formed by B-branch electron transfer in the new mutant is much faster (seconds) than has been previously reported for charge
recombination of P+QB
− trapped in wildtype RCs (105 s) [Kleinfeld et al. (1984b) Biochemistry 23: 5780–5786]. This difference is discussed in light of the different binding
sites for QB and QB
− that recently have been found by X-ray crystallography at cryogenic temperatures [Stowell et al. (1997) Science 276: 812–816].
We present the first low-temperature absorption difference spectrum due to P+QB
−.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
55.
The efficacy of teflubenzuron (Calicide) for the treatment of farmed Atlantic salmon Salmo salar L. infested with sea lice Lepeophtheirus salmonis (Kr?yer, 1838), was investigated at low water temperatures in 2 commercial salmon farms. Calicide, coated on commercial feed pellets, was administered orally at 10 mg kg(-1) d(-1) for 7 consecutive days. Fish were randomly sampled and lice numbers recorded from both treated and control groups on 3 or 4 sampling occasions post-medication. Statistically significant reductions in the number of L. salmonis per fish were recorded. Maximum efficacy was observed toward chalimus and preadult stages of L. salmonis, and was achieved approximately 26 d post-medication. No adverse drug reactions or palatability problems were associated with the treatments. 相似文献
56.
57.
Paola L. Carvajal Monroy Zipora Yablonka-Reuveni Sander Grefte Anne Marie Kuijpers-Jagtman Frank A.D.T.G. Wagener Johannes W. Von den Hoff 《Journal of visualized experiments : JoVE》2015,(101)
Fibrosis and defective muscle regeneration can hamper the functional recovery of the soft palate muscles after cleft palate repair. This causes persistent problems in speech, swallowing, and sucking. In vitro culture systems that allow the study of satellite cells (myogenic stem cells) from head muscles are crucial to develop new therapies based on tissue engineering to promote muscle regeneration after surgery. These systems will offer new perspectives for the treatment of cleft palate patients. A protocol for the isolation, culture and differentiation of satellite cells from head muscles is presented. The isolation is based on enzymatic digestion and trituration to release the satellite cells. In addition, this protocol comprises an innovative method using extracellular matrix gel coatings of millimeter size, which requires only low numbers of satellite cells for differentiation assays. 相似文献
58.
Catharina I. Delebinski Monika Twardziok Susann Kleinsimon Florian Hoff Katharina Mulsow Jana Rolff Sebastian J?ger Angelika Eggert Georg Seifert 《PloS one》2015,10(8)
Aqueous Viscum album L. extracts are widely used in complementary cancer medicine. Hydrophobic triterpene acids also possess anti-cancer properties, but due to their low solubility they do not occur in significant amounts in aqueous extracts. Using cyclodextrins we solubilised mistletoe triterpenes (mainly oleanolic acid) and investigated the effect of a mistletoe whole plant extract on human acute myeloid leukaemia cells in vitro, ex vivo and in vivo. Single Viscum album L. extracts containing only solubilised triterpene acids (TT) or lectins (viscum) inhibited cell proliferation and induced apoptosis in a dose-dependent manner in vitro and ex vivo. The combination of viscum and TT extracts (viscumTT) enhanced the induction of apoptosis synergistically. The experiments demonstrated that all three extracts are able to induce apoptosis via caspase-8 and -9 dependent pathways with down-regulation of members of the inhibitor of apoptosis and Bcl-2 families of proteins. Finally, the acute myeloid leukaemia mouse model experiment confirmed the therapeutic effectiveness of viscumTT-treatment resulting in significant tumour weight reduction, comparable to the effect in cytarabine-treated mice. These results suggest that the combination viscumTT may have a potential therapeutic value for the treatment AML. 相似文献
59.
Birgit Hoff Jens Kamerewerd Claudia Sigl Ivo Zadra Ulrich Kück 《Applied microbiology and biotechnology》2010,85(4):1081-1094
In Penicillium chrysogenum, the industrial producer of the β-lactam antibiotic penicillin, generating gene replacements for functional analyses is very
inefficient. Here, we constructed a recipient strain that allows efficient disruption of any target gene via homologous recombination.
Following isolation of the Pcku70 (syn. hdfA) gene encoding a conserved eukaryotic DNA-binding protein involved in non-homologous end joining (NHEJ), a Pcku70 knockout strain was constructed using a novel nourseothricin-resistance cassette as selectable marker. In detailed physiological
tests, strain ΔPcku70 showed no significant reduction in vegetative growth due to increased sensitivity to different mutagenic
substances. Importantly, deletion of the Pcku70 gene had no effect on penicillin biosynthesis. However, strain ΔPcku70 exhibits higher sensitivity to osmotic stress than
the parent strain. This correlated well with comparative data from microarray analyses: Genes related to the stress response
are significantly up-regulated in the Pcku70 deletion mutant. To demonstrate the applicability of strain ΔPcku70, three genes related to β-lactam antibiotic biosynthesis
were efficiently disrupted, indicating that this strain shows a low frequency of NHEJ, thus promoting efficient homologous
recombination. Furthermore, we discuss strategies to reactivate Pcku70 in strains successfully used for gene disruptions. 相似文献
60.
Stephanie J. Culler Kevin G. Hoff Rodger B. Voelker J. Andrew Berglund Christina D. Smolke 《Nucleic acids research》2010,38(15):5152-5165
Despite the critical role of pre-mRNA splicing in generating proteomic diversity and regulating gene expression, the sequence composition and function of intronic splicing regulatory elements (ISREs) have not been well elucidated. Here, we employed a high-throughput in vivo Screening PLatform for Intronic Control Elements (SPLICE) to identify 125 unique ISRE sequences from a random nucleotide library in human cells. Bioinformatic analyses reveal consensus motifs that resemble splicing regulatory elements and binding sites for characterized splicing factors and that are enriched in the introns of naturally occurring spliced genes, supporting their biological relevance. In vivo characterization, including an RNAi silencing study, demonstrate that ISRE sequences can exhibit combinatorial regulatory activity and that multiple trans-acting factors are involved in the regulatory effect of a single ISRE. Our work provides an initial examination into the sequence characteristics and function of ISREs, providing an important contribution to the splicing code. 相似文献