Isolation and characterization of a xylose-glucose isomerase from a new strain <i>Streptomyces thermovulgaris</i> 127, var. 7-86
Bibliographic record
Abstract
A thermostable D-xylose-glucose isomerase was isolated from the thermophilic strain Streptomyces thermovulgaris 127, var. 7-86, as a result of mutagenic treatment by gamma-irradiation of the parent strain, by precipitation and sequential chromatographies on DEAE-Sephadex A50, TSK-gel, FPLC-Mono Q/HR, and Superose 12 columns. The N-terminal amino acid sequence and amino acid analysis shows 73-92% homology with xylose-glucose isomerases from other sources. The native molecular mass, determined by gel filtration on a Superose 12 column, is 180 kDa, and 44.6 and 45 kDa were calculated, based on amino acid analysis and 10% SDS-PAGE, respectively. Both, the activity and stability of the enzyme were investigated toward pH, temperature, and denaturation with guanidine hydrochloride. The enzyme activity showed a clear pH optimum between pH 7.2 and 9.0 with D-glucose and 7.4 and 8.3 with D-xylose as substrates, respectively. The enzyme is active up to 60-85 degrees C at pH 7.0, using D-glucose, and up to 50-60 degrees C at pH 7.6, using D-xylose as substrates. The activation energy (Ea = 46 kJ x mol(-1)) and the critical temperature (Tc = 60 degrees C) were determined by fluorescence spectroscopy. Tc is in close coincidence with the melting temperature of denaturation (Tm = 59 degrees C), determined by circular dichroism (CD) spectroscopy. The free energy of stabilization in water after denaturation with Gdn.HCl was calculated to be 12 k x mol(-1). The specific activity (km values) for D-xylose-glucose isomerase at 70 degrees C toward different substrates, D-xylose, D-glucose, and D-ribose, were determined to be 4.4, 55.5, and 13.3 mM, 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) | 0.001 | 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".