Redox-Regulation in Chloroplasten: Post-translationale Mechanismen und Feinregulation




Licht-/Dunkelmodulation
Kovalente Redox-Modifikation von Chloroplastenenzymen dient als "Lichtschalter" mit Dimmerfunktion, um Enzymaktivitäten der Assimilation und der Energiedissipation dem Bedarf anzupassen.
    Das Ferredoxin-Thioredoxin-System überträgt Elektronen aus der oxygenen Photosynthese auf Schlüsselenzyme des Chloroplastenstoffwechsels. Diese kovalente Redoxmodifikation ist Grundlage für die individuelle Regulierbarkeit der Zielenzyme. Ihre Redoxpotentiale werden durch Stoffwechsel-Intermediate spezifisch verändert, wodurch die Flüsse jeweils dem Bedarf angepasst werden.
Da die Redoxmodulierbarkeit der Chloroplastenenzyme erst nach der Entstehung der oxygenen Photosynthese etabliert werden konnte, wurden − beginnend mit den Cyanobakterien − redox-modulierte Enzyme aus Organismen verschiedener phylogenetischer Entwicklungsstufen auf das Vorkommen der redox-aktiven Cysteine bzw. der regulatorischen Sequenzbereichen untersucht. Wie für NADP-Malatdehydrogenase, konnte auch für NADP-Glycerinaldehyd-3-P-Dehydrogenase, Phosphoribulokinase, Fruktose-1,6-bisphosphatase und Glukose-6-P-Dehydrogenase gezeigt werden, dass erst im Laufe der Evolution die "perfekt" regulierten Formen entstanden sind. Die reversible Redox-Reaktion an den Zielenzymen ist die Basis für die Feinregulation zur individuellen Anpassung der Stoffwechselflüsse.

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