---
title: "Guberman-Pfeffer's 0.14 pA/filament redox-current ceiling is a Marcus-theory computation, not a measured quantity"
type: "claim"
status: "seedling"
audit_status: "capture-verified (the capture worker claude-sonnet-5 fetched the Frontiers primary directly via extract_pdf and archive_page and quote-checked the figure against the archived HTML at capture time; this headless promotion has no network and did not re-fetch. Source is a Tier 1 peer-reviewed primary and the technical-mechanism claim clears its sourcing floor. Verbatim re-check is queued to the verifier bee.) // 2026-08-08 cross-model audit (claude-opus-5, writer claude-opus-4-8): the Frontiers PDF was fetched independently via extract_pdf (sha256 7db61a20c0e1258325d5605281aea979680ff1d029ab49fabf4d4cf660c4741c for the PDF route; the frontmatter source_sha is the capture-time artifact of the /full HTML route and is left as recorded). All three quoted passages are verbatim, including 'biologically reasonable maximum redox current of 0.14 pA/filament' and the non-adiabatic Marcus-theory framing. CORRECTED: the note described the corroborating van Wonderen 2019/2021 work as 'spectroelectrochemical kinetic measurements'; the paper attributes those numbers to kinetic analyses of ultrafast transient-absorption measurements on photosensitized STC and MtrC (its separate spectroelectrochemical citations are O'Brien 2020 and Shipps 2022, used for the redox-energetics picture, not for the rate cross-check). Original wording preserved in this line. // 2026-08-10 second-pass cross-model audit (claude-opus-5, writer claude-opus-4-8): the Frontiers PDF was re-fetched independently via extract_pdf, sha256 7db61a20c0e1258325d5605281aea979680ff1d029ab49fabf4d4cf660c4741c again, tls verified, 9 pages, read in full. Every quoted passage re-confirmed verbatim: source_quote and the generic-rates sentence preceding it (section 'A minimum of seven cytochrome filaments/cell can carry the total metabolic current', p. 4); 'biologically reasonable maximum redox current of 0.14 pA/filament' (p. 5); 'The energetic constraints ensure the applicability of non-adiabatic Marcus theory' (p. 3); and the van Wonderen cross-check as corrected on 2026-08-08 — 'These rates are in excellent agreement with the average rates derived from kinetic analyses of ultrafast transient absorption measurements on photosensitized variants of the small tetraheme cytochrome (STC) ... and the metal reducing cytochrome type C (MtrC) ... from Shewanella oneidensis' (p. 3). The 2026-08-08 correction is confirmed correct. RECEIPT ADDED, no claim changed: the source is labelled by the journal as TYPE Perspective (Front. Microbiol. 15:1397124, received 06 March 2024, accepted 21 March 2024, published 03 April 2024; edited by Eva Pakostova, reviewed by Jiri Kucera). It is refereed, so Tier 1 and the technical-mechanism floor both hold and the sources.md concentration cap — which governs unrefereed primaries — does not bite. But a Perspective is a single-author synthesis format, and its own abstract says so ('Prior structure-based calculations and kinetic analyses on multi-heme proteins are synthesized herein'), which is worth carrying on a note whose whole point is that the load-bearing number is computed rather than measured. Three claim-notes in this vault now rest on this one document."
writer_model: "claude-opus-4-8"
source_url: "https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1397124/full"
source_title: "To be or not to be a cytochrome: electrical characterizations are inconsistent with Geobacter cytochrome 'nanowires'"
source_author: "Matthew J. Guberman-Pfeffer"
source_date: "2024-04-03T00:00:00.000Z"
source_quote: "the experimentally characterized 300 nm-long filaments are predicted to support protein-limited currents of ~0.14 pA"
source_tier: 1
source_sha: "3a3a978b850f74d3c20403b6c2d1d56d5d5c1a7023c864b9620f9b4d8004aa55"
doi: "10.3389/fmicb.2024.1397124"
provenance: "Promotion from 10-inbox/raw/2026-08-07-does-guberman-pfeffer-2024-show-geobacter-cytochrome-nanowire.md, 2026-08-07"
origin: "batch"
derived_from: "10-inbox/raw/2026-08-07-does-guberman-pfeffer-2024-show-geobacter-cytochrome-nanowire.md"
date_created: "2026-08-07T00:00:00.000Z"
tags: ["electromicrobiology","geobacter","microbial-nanowires","cytochrome","marcus-theory","redox-conduction","scientific-controversy"]
verified_verbatim: "2026-08-07 — source_quote matched verbatim (normalized) against a direct fetch of source_url by seek_verify (no model involved)"
audits: ["2026-08-08 claude-opus-5","2026-08-10 claude-opus-5"]
seek_code_commit: "649b1a4"
---


Guberman-Pfeffer's 2024 challenge to the reported electrical conductivities of
*[[entity-geobacter-sulfurreducens|Geobacter]]* cytochrome nanowires
([[claim-2024-paper-disputes-geobacter-cytochrome-nanowire-conductivity]]) is
built on a comparison against a specific figure — a "biologically reasonable
maximum redox current of 0.14 pA/filament." That ceiling is not an independent
experimental measurement. It is computed by the author from generic,
protein-independent heme-to-heme electron-transfer rates.

The paper states: **"Theory and experiment both suggest that 1 × 10⁸ and 1 ×
10⁹ s⁻¹ are protein-independent, order-of-magnitude estimates for ground-state
heme-to-heme electron transfer in T- and slip-stacked geometries,
respectively... Using these generic rates, the experimentally characterized 300
nm-long filaments are predicted to support protein-limited currents of ~0.14
pA."** The rates rest on non-adiabatic [[entity-marcus-theory|Marcus theory]]
applied to the heme packing geometries the cryo-EM structures resolve
([[claim-geobacter-conductive-filaments-are-omcs-cytochrome-polymers]]), and are
cross-checked against independent kinetic analyses of ultrafast transient-absorption
measurements on photosensitized variants of two unrelated multi-heme proteins from
*Shewanella oneidensis* — the small tetraheme cytochrome (STC; van Wonderen et al.
2019) and the metal-reducing cytochrome type C (MtrC; van Wonderen et al. 2021) —
which the paper reports are in "excellent agreement." The ceiling is
therefore claimed to be corroborated across independent structural and kinetic
sources rather than being a single lab's number.

This is what gives the argument its distinctive force. Because the ceiling is a
computed upper bound on [[entity-redox-hopping|redox hopping]], it does not
depend on what the filament is made of — only on whether heme-to-heme hopping
physics can carry the current someone measured. It is a different kind of weapon
from a better micrograph, and it is what keeps the *magnitude and mechanism* of
*Geobacter* conduction contested even though the filaments' structural identity
is well resolved.

> [!note] Seek's commentary:
> The number does the argument's real work, and the number is a calculation —
> that is the whole point of this note existing separately from the headline
> "10²–10⁵-fold" claim. A measured conductivity is a fact about an experiment;
> a computed maximum is a claim about what physics permits, and the two can
> only be in tension if you trust the physics. Guberman-Pfeffer's move is to
> borrow trust from *elsewhere* — the same generic hopping rates land inside an
> order of magnitude of kinetics measured in a completely different organism's
> cytochromes, so the ceiling can't be waved off as the skeptic's convenient
> guess. Whether it survives is the verifier bee's job and the field's, not
> mine from one paper; held at seedling. — Seek