Nuclear spin is a quantum property that makes an atomic nucleus behave like a tiny magnet. Because of this, a nucleus can interact with nearby electrons and, in principle, alter the outcome of certain chemical reactions. Crucially, spin is not determined by an element’s chemical identity alone. Isotopes of the same element, which carry the same number of protons and electrons and therefore behave almost identically in ordinary chemistry, can differ in the spin of their nuclei. This means two isotopes of a drug could, in theory, produce different biological effects even though a chemist would struggle to tell them apart in a test tube. It is precisely this possibility that the Surrey team set out to investigate for lithium.

Lithium has two stable isotopes, lithium-6 and lithium-7. Chemically, they are near indistinguishable, but their nuclei possess different quantum spins. Intriguingly, previous in vivo animal studies have reported that the two isotopes can produce different biological effects, including differences in their ability to reduce hyperactivity in rats. Those findings have long been difficult to explain within the framework of conventional chemistry, which would predict essentially identical behaviour from the two isotopes. The new study asks whether quantum spin effects could bridge that explanatory gap, providing a theoretical account of how chemically identical atoms might act differently in living systems.

To explore the question, the researchers modelled a chemical reaction involving two molecules that are abundant and biologically important in the brain. The first is flavin, a vitamin B2-derived molecule that helps proteins transfer electrons in a wide range of cellular processes. The second is a radical derived from vitamin C, meaning a form of the molecule that carries a single unpaired electron. Vitamin C is plentiful in neurons, the brain’s principal signalling cells, and helps protect the brain against oxidative stress. Its radical form has a property that makes it especially interesting from a quantum perspective: it can retain its spin state for relatively long periods, giving quantum effects a wider window of opportunity to influence the reaction before the spin information is lost.

The simulations revealed that lithium-6 and lithium-7 could indeed affect this flavin-ascorbyl radical reaction differently, and that the difference stems directly from their contrasting nuclear spins. Perhaps most strikingly, the size of the predicted isotope effect was similar in magnitude to the effects inferred from the earlier animal studies comparing the behavioural consequences of the two lithium isotopes. That agreement between a purely computational prediction and previously observed biological data is what elevates the work from an interesting calculation to a testable scientific hypothesis. It suggests that the quantum mechanism is not merely a theoretical curiosity but operates on a scale that could plausibly matter in biology.

Amina Mouhamed, a PhD researcher at the University of Surrey and first author of the study, described the intellectual appeal of the finding. What fascinated the team, she said, was the possibility that two almost chemically identical forms of lithium could influence biology differently because of a quantum property of their nuclei. She noted that if such a difference could affect chemical reactions and ultimately contribute to changes in behaviour, it would demonstrate a remarkable link across scales, running from atomic nuclei all the way up to biological processes. That possibility, she emphasised, remains to be tested experimentally, but confirming it could open a new avenue for treatment design, in which the action of a medicine is fine-tuned simply by changing its isotopic composition.

Senior author Dr Marco Sacchi, Associate Professor of Computational Chemistry at the University of Surrey, was careful to frame the results within their proper limits. Lithium, he said, is an extraordinary drug that has transformed the treatment of bipolar disorder, yet after decades of clinical use scientists still do not completely understand what it does at the molecular level. He stressed that the results do not show that quantum spin effects are responsible for lithium’s therapeutic action. What they do show, he explained, is that such a mechanism is physically plausible in a biologically relevant molecular system and can generate an isotope effect of the right order of magnitude. That, he argued, gives researchers a hypothesis they can now begin to test experimentally.

The significance of the work extends beyond lithium itself. It sits within the emerging field of quantum biology, which investigates whether quantum mechanical phenomena such as spin, coherence and tunnelling play functional roles in living systems. The best-known example is the proposed radical pair mechanism in bird magnetoreception, in which the spins of electron pairs in light-sensitive proteins are thought to influence how migratory birds sense Earth’s magnetic field. The Surrey study applies a similar logic to a psychiatric drug, raising the provocative question of whether quantum effects in radical pair chemistry could mediate the behavioural and clinical actions of a widely prescribed medicine. If confirmed, it would be one of the clearest demonstrations yet that nuclear spin can shape pharmacology.

The path forward, the researchers suggest, lies in targeted experiments comparing lithium-6 and lithium-7 in systems that involve vitamin C. Such studies could determine whether the isotope-dependent effects predicted by the computational model actually occur in real chemical or biological systems. Success would not only illuminate a possible mechanism behind one of psychiatry’s most important drugs but could also point toward a genuinely novel strategy in drug development: selecting isotopes to tune the quantum behaviour of a therapeutic compound. For now, the study stands as a carefully bounded but compelling proposal, connecting the spin of an atomic nucleus to the chemistry of the brain, and inviting experimentalists to find out whether that connection runs deep enough to matter for patients.

Subject of Research: Quantum nuclear spin effects of lithium isotopes on flavin-ascorbyl radical reactions relevant to brain chemistry

Article Title: Quantum study offers new insights into lithium’s effects in the brain

Article References: Quantum study offers new insights into lithium’s effects in the brain. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: lithium, bipolar disorder, quantum biology, nuclear spin, isotopes, vitamin C, flavin, radical pair, computational chemistry, neuroscience, PLOS One, University of Surrey

Redox cofactors are the molecular batteries of the cell. They accept and donate electrons in the tightly choreographed reactions that underpin respiration, photosynthesis, biosynthesis and detoxification. The canonical cofactors—molecules such as flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP)—are so widespread that their presence in an enzyme active site is often assumed rather than demonstrated. But over the past several years, researchers have identified a series of modified and entirely distinct cofactors: prenylated flavins such as flavin adenine dinucleotide modified with a prenyl group, deazaflavins like F420, quinone-derived cofactors such as topaquinone and tryptophan tryptophylquinone, and metal-organic species that defy easy classification. These noncanonical cofactors enable chemistries that standard flavins and nicotinamides cannot easily achieve, including hydride transfers at unusual redox potentials, radical-mediated rearrangements and C–C bond formations that would be difficult with conventional catalysis.

The central puzzle addressed in the new work is one of recognition and assembly. If an enzyme uses a noncanonical cofactor, how does the protein know to bind that cofactor rather than its more abundant canonical cousin? And how can bioinformaticians predict, from sequence alone, which of the millions of uncharacterized proteins in genomic databases depend on these exotic helpers? The answer, according to the study, lies in a short, recurring sequence motif—a conserved stretch of amino acids that acts as a molecular postcode, directing the enzyme’s cofactor-binding pocket toward noncanonical chemistry.

Sequence motifs have long served as the workhorses of computational biology. Short conserved patterns, such as the P-loop that binds nucleotide phosphates or the zinc-finger motifs that coordinate metal ions in DNA-binding proteins, allow researchers to assign function to proteins that have never been isolated in a laboratory. The newly identified motif performs a similar role for redox cofactor selection. By scanning families of flavin-dependent enzymes and comparing those known to use standard FAD or FMN with the smaller subset confirmed to use modified or alternative cofactors, the researchers identified a conserved pattern of residues that appears with striking regularity in the noncanonical group and is conspicuously absent from the canonical one. Mutational experiments confirmed that altering these residues in a noncanonical enzyme abolished its ability to accommodate the alternative cofactor, while introducing the motif into a canonical scaffold shifted its cofactor preference—a result that establishes the motif as a genuine determinant of cofactor identity rather than a coincidental correlation.

The implications of this finding extend well beyond the specific enzyme families examined in the study. Genomic surveys suggest that proteins carrying the motif are distributed across a remarkable range of organisms, from soil-dwelling actinobacteria—long recognized as prolific producers of bioactive natural products—to human-associated microbes and even some archaeal lineages. In many of these organisms, the motif-bearing enzymes cluster within biosynthetic gene clusters, the compact genomic neighborhoods that encode the assembly lines for antibiotics, antitumor agents and other specialized metabolites. This genomic context hints at a widespread and previously underappreciated role for noncanonical redox chemistry in natural product biosynthesis, suggesting that many of the structurally exotic metabolites isolated from microbes over the past half-century may owe their existence to enzymes quietly using cofactors that standard annotation pipelines would never flag.

One of the most exciting consequences of the work is predictive. Armed with the motif, researchers can now interrogate sequence databases with a simple pattern search and retrieve a curated list of candidate enzymes likely to use noncanonical cofactors. This transforms what has historically been a slow, serendipitous process—discover a strange metabolite, purify the enzyme responsible, and only then realize the cofactor is unusual—into a rational, hypothesis-driven workflow. Biochemistry can then be targeted at the most promising candidates, prioritizing enzymes from gene clusters associated with medicinally relevant compound classes. In an era when the rate of genome sequencing vastly outpaces the rate of experimental characterization, tools that convert sequence information into functional predictions are among the most valuable commodities in the life sciences.

The discovery also carries significant weight for synthetic biology and enzyme engineering. Noncanonical cofactors often possess redox potentials and reactivity profiles that canonical cofactors cannot match. F420, for example, the deazaflavin cofactor best known from methanogenic archaea, mediates hydride transfer reactions at potentials inaccessible to NAD and NADP, and engineered F420-dependent enzymes have already been explored for the degradation of persistent pollutants and the production of pharmaceutical intermediates. Prenylated flavins, meanwhile, catalyze photochemical reactions that ordinary flavins cannot, and their light-driven chemistry is being harnessed in optogenetic tools and photocatalytic cascades. A sequence-level handle on cofactor selection means that protein engineers can now rationally swap cofactor identity in designed enzymes, effectively reprogramming the electrochemical capabilities of a catalytic scaffold without altering its overall fold. This could accelerate the design of biocatalysts for green chemistry, where replacing metal catalysts and harsh reagents with enzyme-based alternatives is a major industrial goal.

From an evolutionary standpoint, the findings raise fascinating questions about how and why biology expanded its redox cofactor repertoire in the first place. The canonical cofactors are ancient, likely predating the last universal common ancestor, and their chemistry is deeply woven into core metabolism. Noncanonical cofactors, by contrast, appear to have arisen as evolutionary innovations in specific ecological and metabolic contexts—perhaps to exploit new redox niches, to escape the thermodynamic constraints of shared metabolic pools, or to protect specialized pathways from cross-talk with housekeeping chemistry. The presence of a dedicated sequence motif suggests that cofactor innovation was accompanied by co-evolution of the protein binding environment, producing a heritable, recognizable signature that could be propagated across enzyme families through duplication and divergence. In this sense, the motif is a fossil record of chemical innovation, preserving in amino acid sequence the memory of evolutionary experiments in electron transfer.

The study also serves as a cautionary tale for genome annotation. Most automated pipelines assign enzyme function by homology, and a protein that resembles a flavin-dependent monooxygenase is typically annotated as such, regardless of which cofactor it actually employs. If a substantial fraction of these enzymes in fact use noncanonical cofactors, then large swaths of existing functional annotations may be subtly or substantially wrong, with consequences for metabolic modeling, pathway reconstruction and the interpretation of gene-expression data. The motif provides a corrective lens, allowing annotators to flag proteins whose cofactor assignments deserve experimental scrutiny. As the authors and commentators in the field note, the lesson is broader: the most abundant cofactors are not necessarily the only ones, and assumptions baked into databases can obscure entire layers of biochemical diversity.

Looking forward, the identification of this sequence motif is likely to catalyze a wave of discovery across several fronts. Experimentalists will purify and characterize motif-bearing enzymes from diverse organisms, likely uncovering new cofactor structures and new reaction types. Computational biologists will refine the motif definition, searching for related patterns that govern the use of other exotic cofactors, and integrating these signals into machine-learning models of enzyme function. Structural biologists will determine how the motif residues reshape the cofactor-binding pocket at atomic resolution, providing design principles for engineered catalysts. And natural products chemists will revisit orphan biosynthetic gene clusters with fresh eyes, suspecting that many of the unexplained transformations encoded within them depend on redox chemistry that no one thought to look for. What began as a search for a short string of amino acids has ended with a map pointing toward a vast, unexplored territory of enzyme chemistry—one that has been hiding in plain sight within the genomes of organisms all around us, waiting only for the right pattern to reveal it.

Subject of Research: A conserved sequence motif that enables natural enzymes to use noncanonical redox cofactors

Article Title: A sequence motif enables widespread use of noncanonical redox cofactors in natural enzymes

Article References: Saleh, S., Hsu, N.-H., Luu, E., Martin, V. C., Ng, H. J. C., Black, W. B., Zhang, S., Kim, J.-K., Sankaran, B., Tran, A. H. T., Hayes, R. L., Siegel, J. B., Qiao, F., & Li, H. (2026). A sequence motif enables widespread use of noncanonical redox cofactors in natural enzymes. Nature Chemical Biology. https://doi.org/10.1038/s41589-026-02315-w

Image Credits: AI Generated

DOI: 10.1038/s41589-026-02315-w

Keywords: redox cofactors, sequence motif, enzymes, flavin, natural product biosynthesis, genome annotation, enzyme engineering, deazaflavin F420, biocatalysis, protein evolution, biosynthetic gene clusters, Nature Chemical Biology