Fluorescence as a tool to understand changes in photosynthetic electron flow regulation

International audienceThe physiological state of a chloroplast is stronglyinfluenced by both biotic and abiotic conditions.Unfavourable growth conditions lead to photosyntheticstress. Chlorophyll a fluorescence is a widelyused probe of photosynthetic activity (specificallyPSII), and therefore stress which specifically targetsthe electron transport pathway and associated alternativeelectron cycling pathways. By manipulating theprocesses that control photosynthesis, affecting thechlorophyll a fluorescence, yields detailed insight intothe biochemicalpathways. Light that is captured by achlorophyll molecule can be utilised in three competingprocesses; electron transport, energy dissipation(via heat) and chlorophyll a fluorescence emission.Electrons produced by water-splitting are not alwaysused in carbon fixation; if the incident irradiancegeneratesmore electrons than the dark reactionscan use in carbon fixation, damage will occur to the photosynthetic apparatus. If carbon fixation is inhibitedby temperature or reduced inorganic carbon (Ci), ATPor NADPH availability, then the photosystem dynamicallyadjusts and uses alternate sinks for electrons, suchas molecular oxygen (water-water cycle or Mehler ascorbateperoxidase reaction). The process of stress acclimationleads to a number of photoprotective pathwaysand we describe how inhibitors can be used to identifythese particular processes. In this chapter, we describethe processes controlling electron transport as influencedby light-induced stress

Cytotoxic Indolocarbazoles from Actinomadura melliaura

Actinomadura melliaura ATCC 39691, a strain isolated from a soil sample collected in Bristol Cove, California, is a known producer of the disaccharide-substituted AT2433 indolocarbazoles (6–9). Reinvestigation of this strain using new media conditions led to >40-fold improvement in the production of previously reported AT2433 metabolites and the isolation and structure elucidation of the four new analogues, AT2433-A3, A4, A5, and B3 (1–4). The availability of this broader set of compounds enabled a subsequent small antibacterial/fungal/cancer SAR study that revealed disaccharyl substitution, N-6 methylation, and C-11 chlorination as key modulators of bioactivity. The slightly improved anticancer potency of the newly reported N-6-desmethyl 1 (compared to 6) contrasts extensive SAR of monoglycosylated rebeccamycin-type topoisomerase I inhibitors where N-6 alkylation has contributed to improved potency and ADME. Complete 2D NMR assignments for the known metabolite BMY-41219 (5) and (13)C NMR spectroscopic data for the known analogue AT2433-B1 (7) are also provided for the first time. [Image: see text

Recent Progress on the Development of Antibiotics from the Genus Micromonospora

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