Pulsed EPR Determination of the Distance between Heme Iron and FMN Centers in a Human Inducible Nitric Oxide Synthase
Bibliographic record
Abstract
Mammalian nitric oxide synthase (NOS) is a homodimeric flavo-hemoprotein that catalyzes the oxidation of L-arginine to nitric oxide (NO). Regulation of NO biosynthesis by NOS is primarily through control of interdomain electron transfer (IET) processes in NOS catalysis. The IET from the flavin mononucleotide (FMN) to heme domains is essential in the delivery of electrons required for O(2) activation in the heme domain and the subsequent NO synthesis by NOS. The NOS output state for NO production is an IET-competent complex of the FMN-binding domain and heme domain, and thereby it facilitates the IET from the FMN to the catalytic heme site. The structure of the functional output state has not yet been determined. In the absence of crystal structure data for NOS holoenzyme, it is important to experimentally determine the Fe...FMN distance to provide a key calibration for computational docking studies and for the IET kinetics studies. Here we used the relaxation-induced dipolar modulation enhancement (RIDME) technique to measure the electron spin echo envelope modulation caused by the dipole interactions between paramagnetic FMN and heme iron centers in the [Fe(III)][FMNH(*)] (FMNH(*): FMN semiquinone) form of a human inducible NOS (iNOS) bidomain oxygenase/FMN construct. The FMNH(*)...Fe distance has been directly determined from the RIDME spectrum. This distance (18.8 +/- 0.1 A) is in excellent agreement with the IET rate constant measured by laser flash photolysis [Feng, C. J.; Dupont, A.; Nahm, N.; Spratt, D.; Hazzard, J. T.; Weinberg, J.; Guillemette, J.; Tollin, G.; Ghosh, D. K. J. Biol. Inorg. Chem. 2009, 14, 133-142].
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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".