The Endothermic Effects during Denaturation of Lysozyme by Temperature Modulated Calorimetry and an Intermediate Reaction Equilibrium
Bibliographic record
Abstract
To gain insight into the thermodynamics of protein denaturation, the complex heat capacity, C p * (= C p ‘ − iC p ‘ ‘) of lysozyme−water system has been measured at pH 2.5 in the 293−368 K range by using temperature-modulated scanning calorimetry (TMSC), a technique in which the thermally reversible enthalpy changes are measured separately and simultaneously with the thermally irreversible enthalpy changes. The plot of C p ‘ against the temperature T shows a broad peak, which is similar to that observed in C p, DSC, measured here and elsewhere by differential scanning calorimetry (DSC), a technique which gives the sum of both the reversible and irreversible contributions in the apparent heat capacity value. This peak in C p, DSC has been generally attributed to endothermic heat absorption on reversible and irreversible unfolding processes and irreversible thermal denaturation. It is shown that the observed C p ‘ peak results from heat absorption when the equilibrium constant between the native lysozyme state and a conformationally different intermediate state increases with T . The plot of C p ‘ versus T is subdivided into four regions, corresponding to the dominance of a certain process. Thermal denaturation of lysozyme was found to occur according to a scheme, native state ↔ unfolded (intermediate) state → denatured state. This conclusion is consistent with the general view that the first step of denaturation of small one-domain globular protein like lysozyme is a reversible conformational (unfolding) transition, and the second step is irreversible denaturation. It is shown that when kept isothermally at T > 341 K, i.e., within the transition temperature range, C p ‘ of lysozyme decreases. This decrease is exponential in time and corresponds to a rate constant, which varies according to the Arrhenius-type equation, with a preexponential factor of 5 × 10 20 s -1 and energy of 167 kJ/mol. The overall kinetics of the denaturation reaction is of the first order.
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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 | 0.001 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| 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".