Cytochrome c-549-an endogenous cofactor of cyclic photophosphorylation in the cyanobacterium Anacystis nidulans? Original paper
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Dr. Umar
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Dr. Umar
Read MoreClinical Pharmacist and Clinical Pharmacy Master’s candidate focused on antibiotic stewardship, AI-driven pharmacy practice, and research that strengthens safe and effective medication use. Experience spans digital health research with Bloomsbury Health (London), pharmacovigilance in patient support programs, and behavioral approaches to mental health care. Published work includes studies on antibiotic use and awareness, AI applications in medicine, postpartum depression management, and patient safety reporting. Developer of an AI-based clinical decision support system designed to enhance antimicrobial stewardship and optimize therapeutic outcomes.
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Dr. Umar
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Researched by:
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Dr. Umar
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Dr. Umar
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Microbiome Signatures identifies and validates condition-specific microbiome shifts and interventions to accelerate clinical translation. Our multidisciplinary team supports clinicians, researchers, and innovators in turning microbiome science into actionable medicine.
Dr. Umar
What was studied?
This original research study tested whether cytochrome c-549 cyclic photophosphorylation can be supported by an endogenous, low-potential c-type cytochrome (cytochrome c-549; midpoint potential ≈ −260 mV) in the cyanobacterium Anacystis nidulans. The authors isolated cytochrome c-549 and compared it with ferredoxin (Fd; ≈ −420 mV), the commonly assumed endogenous mediator of photosystem I-driven cyclic electron flow. Using anaerobic membrane preparations, they quantified ATP formation under far-red light (707 nm) in the presence of DCMU (to block linear electron flow through photosystem II) and then systematically varied both the concentration and the initial redox poise (percent reduced) of the added cofactors. They also used classic electron-transport inhibitors (DBMIB, EDAC, DSPD) and carbon monoxide (CO) to map where cytochrome c-549 and Fd feed into the cyclic pathway and to distinguish cytochrome-mediated from Fd-mediated cycling.
Who was studied
The biological system was the cyanobacterium Anacystis nidulans (also referred to as Synechococcus sp., strain 1402-1). Cells were grown axenically at 38°C in an illuminated turbidostat and maintained in late logarithmic phase, a growth stage relevant because cytochrome c-549 is reported to accumulate strongly in late log and stationary phases (approaching tens of micromolar intracellularly). The experiments were performed on isolated membrane preparations generated by French press disruption of lysozyme-treated cells and high-speed sedimentation, with chlorophyll-normalized membrane suspensions assayed under oxygen-free nitrogen to prevent spontaneous oxidation of reduced cofactors.
Most important findings
Cyclic photophosphorylation required appropriate redox poising of the soluble cofactor: both cytochrome c-549 and ferredoxin drove maximal ATP formation when added ~50% reduced, while fully oxidized or fully reduced cytochrome c-549 was much less effective (a similar, though somewhat less dramatic, effect was seen with Fd). Under optimized conditions, Fd was only ~30% more efficient than cytochrome c-549, indicating cytochrome c-549 can function as a high-capacity mediator rather than a marginal side pathway. Inhibitor profiling suggested both mediators pass electrons from photosystem I toward plastoquinone and cytochrome f (DBMIB and EDAC strongly inhibited both). Crucially, pathway selectivity differed: DSPD selectively inhibited Fd-mediated cycling, whereas CO selectively inhibited cytochrome c-549–mediated cycling, consistent with CO binding to low-potential c-type cytochromes and providing strong functional evidence that cytochrome c-549 itself is the operative mediator in that condition. Together, these data support cytochrome c-549 as a plausible endogenous cofactor for cyclic photophosphorylation—particularly in late growth phases when it is abundant and when its redox state in vivo could be maintained near the optimal mid-reduced range.
| Microbial feature | Study-relevant association |
|---|---|
| Anacystis nidulans | Performs cyclic photophosphorylation via photosystem I under anaerobic conditions |
| Cytochrome c-549 (−260 mV) | Supports high cyclic ATP formation when ~50% reduced; CO-sensitive pathway |
| Ferredoxin (−420 mV) | Supports cyclic ATP formation; DSPD-sensitive pathway; slightly higher maximal rates |
| Plastoquinone/cytochrome f step | Shared route inferred from strong inhibition by DBMIB and EDAC |
Key implications
Although not a host-associated “microbiome” study, this work is highly relevant to microbial energy-metabolism signatures: it identifies a specific redox protein (cytochrome c-549) whose presence and redox poise can switch the efficiency and inhibitor sensitivity of cyclic photophosphorylation in a cyanobacterium. For clinicians and translational microbiome scientists, the practical lesson is that microbial functional capacity is often conditionally dependent not just on gene/protein abundance but on environmental redox context (oxygen tension, electron donor/acceptor availability). In a microbiome signatures database, cytochrome c-549–c-549-like low-potential c-type cytochromes could be annotated as markers of flexible phototrophic or redox-responsive energy conservation strategies, potentially influencing community persistence in fluctuating oxygen niches.
Citation
Kienzl PF, Peschek GA. Cytochrome c-549—an endogenous cofactor of cyclic photophosphorylation in the cyanobacterium Anacystis nidulans? FEBS Lett. 1983;162(1):76-80