Binding of Polyaminocarboxylate Chelators to the Active-Site Copper Inhibits the GSNO-Reductase Activity but Not the Superoxide Dismutase Activity of Cu,Zn-Superoxide Dismutase
Bibliographic record
Abstract
In addition to its superoxide dismutase (SOD) activity, Cu,Zn-superoxide dismutase (CuZnSOD) catalyzes the reductive decomposition of S-nitroso-L-glutathione (GSNO) in the presence of thiols such as L-glutathione (GSH). The GSNO-reductase activity but not the superoxide dismutase (SOD) activity of CuZnSOD is inhibited by the commonly used polyaminocarboxylate metal ion chelators, EDTA and DTPA. The basis for this selective inhibition is systematically investigated here. Incubation with EDTA or DTPA caused a time-dependent decrease in the 680 nm d-d absorption of Cu(II)ZnSOD but no loss in SOD activity or in the level of metal loading of the enzyme as determined by ICP-MS. The chelators also protected the SOD activity against inhibition by the arginine-specific reagent, phenylglyoxal. Measurements of both the time course of SNO absorption decay at 333 nm and oxymyoglobin scavenging of the NO that is released confirmed that the chelators inhibit CuZnSOD catalysis of GSNO reductive decomposition by GSH. The decreased GSNO-reductase activity is correlated with decreased rates of Cu(II)ZnSOD reduction by GSH in the presence of the chelators as monitored spectrophotometrically at 680 nm. The aggregate data suggest binding of the chelators to CuZnSOD, which was detected by isothermal titration calorimetry (ITC). Dissociation constants of 0.08 +/- 0.02 and 8.3 +/- 0.2 microM were calculated from the ITC thermograms for the binding of a single EDTA and DTPA, respectively, to the CuZnSOD homodimer. No association was detected under the same conditions with the metal-free enzyme (EESOD). Thus, EDTA and DTPA must bind to the solvent-exposed active-site copper of one subunit without removing the metal. This induces a conformational change at the second active site that inhibits the GSNO-reductase but not the SOD activity of the enzyme.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".