Roles of K<sup>+</sup>, H<sup>+</sup>, H<sub>2</sub>O, and ΔΨ in Solute Transport Mediated by Major Facilitator Superfamily Members ProP and LacY
Bibliographic record
Abstract
H (+)-solute symporters ProP and LacY are members of the major facilitator superfamily. ProP mediates osmoprotectant (e.g., proline) accumulation, whereas LacY transports the nutrient lactose. The roles of K (+), H (+), H 2O, and DeltaPsi in H (+)-proline and H (+)-lactose symport were compared using right-side-out cytoplasmic membrane vesicles (MVs) from bacteria expressing both transporters and proteoliposomes (PRLs) reconstituted with pure ProP-His 6. ProP activity increased as LacY activity decreased when osmotic stress (increasing osmolality) was imposed on MVs. The activities of both transporters decreased to similar extents when Na (+) replaced K (+) in MV preparations. Thus, K (+) did not specifically control ProP activity. As with LacY, an increasing extravesicular pH stimulated ProP-mediated proline efflux much more than ProP-mediated proline exchange from de-energized MVs. In contrast to that of LacY, ProP-mediated exchange was only 2-fold faster than ProP-mediated efflux and was inhibited by respiration. In the absence of the protonmotive force (Deltamu H (+) ), efflux of lactose from MVs was much more sensitive to increasing osmolality than lactose exchange. Thus, H 2O may be directly involved in proton transport via LacY. In the absence of Deltamu H (+) , proline efflux and exchange from MVs were osmolality-independent. In PRLs with a DeltapH of 1 (lumen alkaline), ProP-His 6 was inactive when the membrane potential (DeltaPsi) was zero, was active but insensitive to osmolality when DeltaPsi was -100 mV, and became osmolality-sensitive as DeltaPsi increased further to -137 mV. ProP-His 6 had the same membrane orientation in PRLs as in cells and MVs. ProP switches among "off", "on", and "osmolality-sensitive" states as the membrane potential increases. Kinetic parameters determined in the absence of Deltamu H (+) represent a ProP population that is predominantly off.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot 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.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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 teacher head, 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".