Two-Enzyme Pathway Links <scp>l</scp>-Arginine to Nitric Oxide in <i>N</i>-Nitroso Biosynthesis
Bibliographic record
Abstract
Nitric oxide (NO) has wide-ranging roles in biology, but less is known about its role in building chemical diversity. Here we report a new route to NO from the biosynthetic pathway to the N -nitroso compound streptozocin. We show that the N -nitroso group of streptozocin comes from the biosynthetic reassembly of l -arginine, with the guanidino nitrogens forming a nitrogen–nitrogen bond. To understand this biosynthetic process, we identify the biosynthetic gene cluster of streptozocin and demonstrate that free l -arginine is N -methylated by StzE to give N ω -monomethyl- l -arginine. We show that this product is then oxidized by StzF, a nonheme iron-dependent enzyme unrelated to known nitric oxide synthases, generating a urea compound and NO. Our work implies that formation and capture of NO is the likely route to N -nitroso formation in vivo. Altogether, our work unveils a new enzyme pair for the production of NO from l -arginine and sets the stage for understanding biosynthetic routes to N -nitroso natural products.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".