In Vitro Phosphorylation of Phosphoenolpyruvate Carboxylase from the Green Alga Selenastrum minutum
Bibliographic record
Abstract
Previously, we described two distinct classes of phosphoenolpyruvate carboxylase (PEPC) isoforms in the green alga Selenastrum minutum. Class 1 PEPC (PEPC1) is a homotetramer composed of 102 kDa subunits (p102), whereas Class 2 PEPCs exist as three large protein complexes (PEPC2-PEPC4) containing varying proportions of structurally dissimilar p102 and 130 kDa (p130) PEPC catalytic subunits. In the current study, a p102 calcium-independent protein kinase was shown to co-purify with PEPC1, but not PEPC2. However, the p130 subunit of PEPC2 was phosphorylated in vitro during its incubation in the presence of [gamma-(32)P]ATP and a clarified algal extract. Treatment of purified PEPC2 with protein phosphatase 2A(2) increased its apparent M(r) as judged by Superose 6 gel filtration chromatography. The presence of the protein phosphatase inhibitors NaF and microcystin-LR throughout PEPC purification significantly influenced the activity and structural organization of Class 2, but not Class 1, PEPC isoforms. The results are consistent with the notion that under the culture conditions employed: (i) Class 1 and Class 2 PEPC isoforms exist in vivo mainly in their dephosphorylated and phosphorylated forms, respectively, and (ii) phosphorylation of Class 2 PEPCs leads to a significant reduction in their activity and native M(r). We propose that protein kinase-mediated phosphorylation is involved in the control and structural organization of green algal PEPC.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".