The Protein Environment of the Bacteriopheophytin Anion Modulates Charge Separation and Charge Recombination in Bacterial Reaction Centers
Bibliographic record
Abstract
The kinetics and pathway of electron transfer has been explored in a series of reaction center mutants from Rhodobacter sphaeroides, in which the leucine residue at M214 near the bacteriopheophytin cofactor in the A-branch has been replaced with methionine, cysteine, alanine, and glycine. These amino acids have substantially different volumes, both from each other and, except for methionine, from the native leucine. Though the mutation site of M214 is close to the bacteriopheophytin cofactor, which is involved in the electron transfer, none of the mutations alter the cofactor composition of the reaction center and the primary charge separation reaction is essentially undisturbed. However, the kinetics of electron transfer from HA(-) → QA becomes both slower and substantially heterogeneous in three of the four mutants. The decreased HA(-) → QA electron transfer rate allows charge recombination between P(+) and HA(-) to compete with the forward reaction, resulting in a drop in the overall yield of charge separation. Both the yield change and the variation in kinetics correlate well with the volume of the mutant amino acid side chains. Analysis of the kinetics suggests that the introduction of a smaller side chain at M214 results in greater protein structural heterogeneity and dynamics on multiple time scales, resulting in perturbation of the electronic environment and its evolution in the vicinity of the early charge-separated radical pair, P(+)HA(-), and the subsequent acceptor QA, affecting both the extent and time scale of dielectric relaxation. It appears that the reaction center has been optimized not only in terms of its static structure-function relationships, but also finely tuned to favor particular reaction pathways on particular time scales by adjusting protein dynamics.
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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 | 0.000 |
| 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".