Open mitochondrial research · Plain-language explainer

Published on Zenodo · October 11, 2026

Finite POLGB Capacity Exposes a Conditional Gain Boundary in POLG Catalytic-Subunit Turnover

Friedl, Andrew

Abstract

**Background:** POLG disease-biology interpretation can conflate catalytic-subunit import, total POLGA abundance, POLGB association, active DNA engagement and synthesis readouts. A finite accessory-capacity model creates a narrower question: whether exact total-POLGA and synthesis trajectories can identify assembly, loss and capacity parameters, and which gain calibration remains unresolved.

**Objective:** This working paper retains the selected question: In a declared POLG catalytic-subunit turnover model with finite POLGB, known imported input and absolute total POLGA, which assembly, loss and capacity parameters are conditionally recoverable from a constant-gain synthesis signal, which activity quantity still needs gain calibration, and how does the matched pseudo-first-order buffered limit erase the nonlinear coefficient information?

**Methods:** Current primary-literature verification and archived primary texts were used only to bound claims. A deterministic synthetic ODE analysis replayed the declared finite-POLGB model with seven capacity values, two constant synthesis gains, three matched-family settings, two derivative-perturbation magnitudes and 99 automated checks. No patient data, fitted biological rates, pooled effect size, treatment ranking, rescue efficacy claim or clinical inference was generated.

**Results:** The replayed analysis passed 99 of 99 deterministic checks. In full-rank finite-capacity trajectories, the coefficient inverse recovered assembly, dissociation, free loss, associated loss, capacity and the effective synthesis coefficient κ with maximum reported exact-recovery error below 1e-5. Constant detector-gain changes left recovered assembly, loss and capacity parameters unchanged while scaling recovered κ. Equal gain-activity products produced identical total and synthesis outputs, so effective per-associated-pool activity k was not separated from detector gain g. As capacity increased from 4 to 1,000,000 at fixed pseudo-first-order assembly a, nonlinear coefficients r and s decreased from 0.2 and 0.1667 to 8e-7 and 6.667e-7, and the relative coefficient condition increased from 218.9 to 31,014,096.9.

**Conclusions:** The result is a conditional mathematical discriminator, not biological validation. Under the declared POLG model, absolute total POLGA, known imported input and a constant-gain synthesis signal can be sufficient for assembly, loss and capacity recovery, while effective per-associated-pool activity remains gain-confounded unless detector gain is known. Knowing detector gain would separate g from the effective coefficient k in this model, but would not by itself establish intrinsic kcat or the active enzyme fraction. Application to purified assays, cells, organoids, animals or patients requires separate proof of input calibration, total-protein calibration, active-pool meaning, POLGB capacity, free-enzyme activity and gain stability.

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DOI: 10.5281/zenodo.23300190

The paper at a glance

The question

POLG studies can measure import, protein amount, accessory-subunit binding or DNA synthesis. Those measurements do not always answer the same question.

Main takeaway

In the ideal model, exact total POLGA and synthesis readouts can recover assembly, loss and capacity terms. The effective activity coefficient still cannot be separated from detector gain unless that gain is calibrated.

Important caution

The work does not show that a drug rescues POLG disease, does not estimate patient benefit and does not prove that real cells follow this model.

Why this matters

POLG studies can measure import, protein amount, accessory-subunit binding or DNA synthesis. Those measurements do not always answer the same question.

How the research was done

The paper studied a mathematical model, not people or animals. POLGA is the catalytic protein made by POLG. POLGB is an accessory protein that can help POLGA work and remain stable.

What the researchers found

In the ideal model, exact total POLGA and synthesis readouts can recover assembly, loss and capacity terms. The effective activity coefficient still cannot be separated from detector gain unless that gain is calibrated.

What this does not prove

The work does not show that a drug rescues POLG disease, does not estimate patient benefit and does not prove that real cells follow this model.

What researchers should test next

A useful validation study would measure imported POLGA, total POLGA, active enzyme state and synthesis signal in the same system over time.

See the evidence

Visual findings

Visual finding 1. Figure 1 analysis-process source image
Visual finding 2. Figure 2 concept-summary source image

Inspect the evidence

Key tables from the paper

Evidence-coded synthesis

CitationModelObserved evidenceInterpretive limit
PEO POLGA variants, HEK293T import assay, mouse model, purified primer-extension assayThe source reports mixed rescue involving aggregation, MITOL/import-associated endpoints and in vitro polymerisation activity.Separate import and activity assays do not provide matched dynamic imported input, total POLGA and synthesis trajectories for the inverse.
Purified POLG variant enzyme assays and DNA-binding measurementsInitial rates were normalized by active enzyme-DNA complex concentration measured under kinetic-assay conditions.Associated POLGA/POLGB cannot be equated with active DNA-engaged enzyme, and detector gain remains separate from intrinsic activity.
Purified PolG and PolG2 proteins with LonP1 proteolysisAssociation-dependent protection from LonP1 motivates different free and associated POLGA loss terms.Purified proteolysis does not calibrate cellular first-order turnover constants or validate zero free-POLGA output.
Mouse PolgA449T/A449T tissues and related human A467T biochemical contextThe source links impaired POLGB interaction to catalytic-subunit depletion and LONP1 susceptibility.The genotype context motivates protection qualitatively; no synthetic parameter is assigned to A449T, A467T or any patient.
Nonlinear dynamic systems-biology identifiability methodologyThe paper establishes identifiable parameter combinations and independent measurements as experiment-design tools.Coefficient inversion is established mathematics; the contribution here is only the bounded POLG observation-map application.
Purified PolG2-DNA and PolG holoenzyme biochemical assaysActivity isotherms and binding measurements already interrogate accessory-subunit dependence.A fixed usable-dimer capacity is a simplifying model assumption, not a direct measurement of all POLGB biology.
Finite ligand-depletion structural-identifiability modelsWhite, Rottschaefer and Bridge already show that nonlinear finite-depletion counterparts can restore identifiability.The present model is not a first general finite-depletion result; it adds only a POLG-specific imported-input and gain-boundary calculation.

Exact recovery, conditioning and derivative perturbation

Brssynthesis design cond.coefficient cond.log-param cond.rank1e-6 derivative inverse
40.20.1667103.8218.9817.76k err 7.847e-06; B err 2.570e-06
100.080.0666796.22380.514756k err 1.393e-05; B err 1.055e-06
1000.0080.00666792.5531571.240e+046k err 1.126e-04; B err 5.231e-05
10008.000e-046.667e-0492.243.107e+041.221e+056k err 0.001105; B err 5.631e-04
100008.000e-056.667e-0592.213.102e+051.219e+066k err 0.01131; B err 0.005588
1000008.000e-066.667e-0692.213.101e+061.218e+076k err 0.152; B err 0.04182
10000008.000e-076.667e-0792.213.101e+071.219e+085invalid

For non-specialists

What this could mean for patients and families

This is a research-methods paper. It should not be used to choose treatment. Its value is in making future POLG experiments more careful about what each measurement can and cannot prove.

  • Does this paper test a treatment in patients?
  • Which POLG measurement was modeled?
  • Why does detector gain matter?
  • What evidence would be needed before biological claims are stronger?