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Mechanisms of Horseradish Peroxidase and α-Chymotrypsin

2013· article· en· W2318713952 on OpenAlex
H. Brian Dunford

Why this work is in the frame

A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.

affAt least one author lists a Canadian institution in the pinned OpenAlex snapshot.

Bibliographic record

VenueProgress in Reaction Kinetics and Mechanism · 2013
Typearticle
Languageen
FieldBiochemistry, Genetics and Molecular Biology
TopicPhotosynthetic Processes and Mechanisms
Canadian institutionsUniversity of Alberta
Fundersnot available
KeywordsChemistryProton-coupled electron transferProtonPhotochemistryPorphyrinElectron transferStereochemistry

Abstract

fetched live from OpenAlex

The pH range for Compound I formation of horseradish peroxidase (2.5 to 11) is the largest for any known enzyme reaction. A key part of the reaction is proton transfer from hydrogen peroxide to distal His42. This proton is retained to complete formation of a water leaving group as the ferryl porphyrin π-cation radical is formed. How can the imidazolium side chain of His42 retain a proton at very high pH? And how can it give up the proton when required at very low pH? The answer is rearrangement of electronic charge through Electron Density Circuits (EDCs) in the protein matrix. An increase of at least 9 p K a units, which occurs on the imidazole side chain of His42 as the Compound I reactive intermediate is formed, is facilitated by an EDC. A reverse EDC facilitates proton transfer to form the water leaving group. The pathway of the EDC involves the heme, its propionate side chains, Arg41, and His42. The occurrence of EDCs in chymotrypsin reactions reinforces the nucleophilic attack, and the subsequent electron and proton transfers. They also can shift p K a values. The catalytic triad of chymotrypsin is Ser195, His57, and Asp102. The currently accepted one-proton transfer mechanism involves Ser195 and His57, with Asp102 being regarded as too acidic to accept a proton. A comparatively small shift in the p K a value of Asp102 is all that is required to make it a proton acceptor from His57 so a two-proton mechanism may occur.

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.

Full frame distilled prediction

Teacher imitation

Not calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.

metaresearch head score (Codex)0.000
metaresearch head score (Gemma)0.000
Version: codex-gemma-dda1882f352aValidation status: machine_predicted_unvalidated
Candidate categoriesnone
Consensus categoriesnone
DomainCandidate signal: none · Consensus signal: none
Study designCandidate signal: Bench or experimental · Consensus signal: Bench or experimental
GenreCandidate signal: Empirical · Consensus signal: Empirical
Teacher disagreement score0.025
Threshold uncertainty score0.650

Codex and Gemma teacher scores by category

CategoryCodexGemma
Metaresearch0.0000.000
Meta-epidemiology (narrow)0.0000.000
Meta-epidemiology (broad)0.0000.000
Bibliometrics0.0000.000
Science and technology studies0.0000.000
Scholarly communication0.0000.000
Open science0.0000.000
Research integrity0.0000.000
Insufficient payload (model declined to judge)0.0000.000

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.

Opus teacher head0.007
GPT teacher head0.231
Teacher spread0.225 · how far apart the two teachers sit on this one work
Validation statusscore_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it