Molecular cloning and characterization of norcoclaurine synthase, an enzyme catalyzing the first committed step in benzylisoquinoline alkaloid biosynthesis
Bibliographic record
Abstract
(S)-Norcoclaurine synthase (NCS) (EC 4.2.1.78) catalyzes the condensation of 3,4-dihydroxyphenylethylamine (dopamine) and 4-hydroxyphenylacetaldehyde (4-HPAA) as the first committed step in the biosynthesis of benzylisoquinoline alkaloids such as morphine, sanguinarine, and berberine, in plants. A molecular clone encoding NCS was isolated from a meadow rue (Thalictrum flavum ssp. glaucum) cell suspension culture cDNA library. Heterologous expression of the NCS cDNA, truncated to remove a putative signal peptide, produced a recombinant protein with NCS activity. Recombinant NCS showed sigmoidal saturation kinetics for dopamine (Hill coefficient=1.98), hyperbolic saturation kinetics for 4-HPAA (Km of 700 microm), and pH and temperature optima of 7.0 and 40 degrees C, respectively, all similar to the purified, plant-derived enzyme. NCS exhibits 28-38% identity, and putative structural homology, with the Bet v 1 allergen and pathogenesis-related (PR)10 protein families. NCS also displays 35% identity with the enzyme (HYP1) responsible for hypericin biosynthesis in St John's wort (Hypericum perforatum). The novel catalytic functions of NCS and HYP1 define a new class of plant secondary metabolic enzymes within the Bet v 1 and PR10 protein families. Weaker homology was also detected between NCS and proteins identified in the latex of Papaver somniferum (opium poppy), and in Arabidopsis thaliana. A family of three to five NCS genes is abundantly expressed in the rhizome, followed by petioles and roots of T. flavum. NCS transcripts were localized to the immature endodermis and pericycle in roots, and the protoderm of leaf primordia in rhizomes; thus, the sites of NCS gene expression and berberine accumulation are temporally and spatially separated in roots and rhizomes respectively.
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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 | 0.001 |
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".