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Food quality effects of unsaturated fatty acids on larvae of the zebra mussel Dreissena polymorpha
(2002)
In standardized growth experiments, newly hatched larvae of the zebra mussel Dreissena polymorpha were fed diets representing different biochemical compositions. Algae that were rich in (n-3) polyunsaturated fatty acids (PUFAs), except for long-chained (.C18) PUFAs (Chlorella minutissima and Monoraphidium minutum) were of low food quality. Higher growth than on C. minutissima or M. minutum was supported by a culture of the cyanobacterium Aphanothece sp., which contained traces of a long-chained (n-3) PUFA, docosahexaenoic acid (DHA, 22 : 6n-3). The alga Isochrysis aff. galbana, which contained high amounts of the longchained (n-3) PUFAs DHA and eicosapentaenoic acid (EPA, 20 : 5n- 3), supported the highest growth. The alga Nannochloropsis limnetica, which differed from I. galbana by a defi- ciency in DHA, allowed slightly, but significantly lower, growth. Growth of larvae on N. limnetica was increased by enrichment of N. limnetica cells with a lipid extract of I. galbana, showing that larval growth on N. limnetica was limited by the deficiency of a compound that was present in I. galbana. Growth was also enhanced by feeding N. limnetica cells supplemented with DHA, but not by cells enriched with EPA, indicating that DHA was the limiting factor. We conclude that, on DHA-deficient food, the larvae of D. polymorpha were not able to sufficiently convert C18-PUFAs into long- chained (n-3) PUFAs and that the rates for elongation and desaturation of EPA into DHA limited growth.
Presentacion
(2002)
Johann Stuve (1752-1793)
(2002)
Vom Auftauchen Amerikas zum Verschwinden Europas : amerikanische Träume von Kolumbus bis Baudrillard
(2002)
Kritische Stellungnahme zur Darstellung des Systems GAT in Norbert Dittmars Buch "Transkription"
(2002)
Junge Lesben und Schwule : zwischen Heteronormativität und posttraditionaler Vergesellschaftung
(2002)
Fremdverstehen im Spannungsfeld von Geschichte und Fremdsprachen. Forschungsgegenstand und Methodik
(2002)
Mathematik : Analysis ; Handbuch für den Unterricht ; Gymnasiale Oberstufe, NRW [Schülerbuch]
(2002)
Pawlowsche Reflexe : Judentum und der Nahostkonflikt ; zu der Terrordebatte in den deutschen Medien
(2002)
Schaddaj - Hüter der Türen Israels : jüdische Frömmigkeit im Alltag und Schabbat im 19. Jahrhundert
(2002)
Geisteswissenschaftliche Pädagogik in historischer Reflexion : ein Interview mit Wolfgang Klafki
(2002)
Politische Bildung
(2002)
Romancing the condition of england : making the academic novel work in the literary market place
(2002)
Die Stimme lesen
(2002)
Two Hybrid cDNA Cloning
(2002)
Chitinase B (ChiB) from Serratia marcescens is a family 18 exochitinase whose catalytic domain has a TIM-barrel fold with a tunnel-shaped active site. We have solved structures of three ChiB complexes that reveal details of substrate binding, substrateassisted catalysis, and product displacement. The structure of an inactive ChiB mutant (E144Q) complexed with a pentameric substrate (binding in subsites 22 to 13) shows closure of the ''roof'' of the active site tunnel. It also shows that the sugar in the 21 position is distorted to a boat conformation, thus providing structural evidence in support of a previously proposed catalytic mechanism. The structures of the active enzyme complexed to Allosamidin (an analogue of a proposed reaction intermediate) and of the active enzyme soaked with pentameric substrate show events after cleavage of the glycosidic bond. The latter structure shows reopening of the roof of the active site tunnel and enzyme-assisted product displacement in the 11 and 12 sites, allowing a water molecule to approach the reaction center. Catalysis is accompanied by correlated structural changes in the core of the TIM barrel that involve conserved polar residues whose functions were hitherto unknown. These changes simultaneously contribute to stabilization of the reaction intermediate and alternation of the pKa of the catalytic acid during the catalytic cycle.