Mitochondrial Signaling: Nitric Oxide Synthesis by Cytochrome c Oxidase and Its Oxygen Sensitivity Are Modulated by Adenine Nucleotides

Verdict. Nitrite can be reduced to nitric oxide (NO) by several heme- and molybdenum-containing proteins, including mitochondrial cytochrome c oxidase (Cco). It intersects mitochondrial stress/dysfunction themes (systemic metabolic stress).

What the authors report

ADP and ATP differentially modulated Cco/NO activity, and ADP extended measurable NO formation across the entire oxygen range tested, up to the assay ceiling of 175 uM O2. Nucleotide regulation was also isoform-dependent: ATP slightly inhibited Va-containing Cco but strongly stimulated Vb-containing Cco under anoxic conditions.

Key results stated in the abstract include the following. Nitrite can be reduced to nitric oxide (NO) by several heme- and molybdenum-containing proteins, including mitochondrial cytochrome c oxidase (Cco). This activity, designated Cco/NO, has been implicated in hypoxic signaling, but its regulation and quantitative significance relative to other NO-producing systems remain uncertain. We examined its modulation by adenine nucleotides using detergent-solubilized yeast and mouse brain mitochondria supplied with 1 mM nitrite and an ascorbate/TMPD/cytochrome c electron-donor system.

Why it matters for mitochondrial biology

Within mitochondrial research, this work maps primarily to apoptosis, redox biology, metabolism, neurobiology. It is relevant to mitochondrial dysfunction discourse because the abstract invokes systemic metabolic stress. That does not by itself establish a validated disease mechanism; it indicates thematic proximity. Server: biorxiv. Posted 2026-08-10. Synthesis confidence is bounded by abstract completeness.

Study design (abstract-level)

ADP and ATP differentially modulated Cco/NO activity, and ADP extended measurable NO formation across the entire oxygen range tested, up to the assay ceiling of 175 uM O2. Rates normalized to cytochrome aa3 demonstrate multi-turnover nitrite-reductase capacity under these substrate-driven assay conditions. Both the cellular ADP/ATP ratio and subsequently assayed Cco/NO activity increased transiently following a hypoxic shift.

Principal findings

1. Nitrite can be reduced to nitric oxide (NO) by several heme- and molybdenum-containing proteins, including mitochondrial cytochrome c oxidase (Cco).
2. This activity, designated Cco/NO, has been implicated in hypoxic signaling, but its regulation and quantitative significance relative to other NO-producing systems remain uncertain.
3. We examined its modulation by adenine nucleotides using detergent-solubilized yeast and mouse brain mitochondria supplied with 1 mM nitrite and an ascorbate/TMPD/cytochrome c electron-donor system.
4. Rates normalized to cytochrome aa3 demonstrate multi-turnover nitrite-reductase capacity under these substrate-driven assay conditions.
5. These findings establish metabolic and isoform-dependent gating of the catalytic capacity of Cco/NO; they do not establish its fractional contribution to total cellular NO or its operation at physiological nitrite concentrations in intact, coupled mitochondria.

Limitations of this brief

• This Mitos brief is an abstract-level synthesis of a preprint; it is not peer review and not a substitute for reading the full paper.
• Preprint status: findings may change with revision or journal review.
• Effect sizes, n numbers, statistics, and full experimental controls are typically incomplete at abstract resolution.
• Comparator/control language is weak or absent in the abstract, limiting causal inference from this brief alone.
• Evidence appears non-human or in vitro from the abstract; translational claims require independent scrutiny.
• Primary source: biorxiv DOI 10.64898/2026.08.09.743791 (posted 2026-08-10).

Open scientific questions

• Which specific experimental panels in the full paper establish the strongest causal claim, and how robust are the controls?
• Is the mitochondrial phenotype cell-autonomous in neurons/glia, or secondary to systemic/inflammatory signals?
• How do these findings sit relative to prior literature on the same pathway—replication, contradiction, or incremental extension?

Bottom line

For mitochondrial biologists focused on apoptosis, redox biology, metabolism, this preprint is worth full-text review if the topic matches your program. Abstract-level takeaway: Nitrite can be reduced to nitric oxide (NO) by several heme- and molybdenum-containing proteins, including mitochondrial cytochrome c oxidase (Cco). Confirm methods, effect sizes, and controls in the full PDF before citing the result as established.

Bibliographic record

Abstract-based editorial synthesis by Mitos. Not peer review.