Molecular Characterization of a First Human 3(α→β)-Hydroxysteroid Epimerase
Bibliographic record
Abstract
In this report, we describe the isolation and characterization of a cDNA encoding an enzyme that exhibits catalytic characteristics of a 3(alpha-->beta)-hydroxysteroid epimerase (3(alpha-->beta)-HSE). The enzyme overexpressed in human 293 embryonic kidney cells transforms androsterone into epi-androsterone in two steps: the oxidation of androsterone to 5 alpha-androstane-3,17-dione, followed by the reduction of the latter to epi-androsterone. The reverse reaction, 3(beta-->alpha)-hydroxysteroid epimeration, is approximately 10-fold weaker. These results are confirmed by V(max)/K(m) determination, which shows that the enzyme catalyzes the oxidation of androsterone to 5 alpha-androstane-3,17-dione and the reduction of 5 alpha-androstane-3,17-dione to epi-androsterone more efficiently than the reverse reactions. The selective catalysis of the reaction following the 3(alpha-->beta) direction is also observed in intact transfected cells in culture, which better reflect physiological conditions. In vitro assays reveal that the recombinant enzyme prefers NAD(+) and NADH as cofactors and could recognize both C-19 and C-21 3 alpha-hydroxysteroids as substrates. DNA sequence analysis predicts a protein of 317 amino acids. Tissue distribution analysis using RT-PCR reveals that the mRNA of the enzyme is expressed in various tissues, including liver, brain, prostate, adrenal, and uterus, with the most abundant expression in the liver. Because active hydroxysteroids generally exert their effect in a stereo-specific manner, 3(alpha-->beta)-HSE could thus potentially play an important role in regulating the biological activities of various steroids.
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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) | 0.001 | 0.002 |
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".