Electron Transport Chain
The electron transport chain (ETC) is the τ-categorical oxidoreductase cascade that converts the reducing power of NADH and FADH₂ into a proton gradient. Categorically, it is the upstream half of oxidative phosphorylation: a series of four membrane-embedded complexes (I-IV) that move electrons stepwise toward O₂, releasing free energy in pump-sized increments and transducing it into transmembrane H⁺ flux.
τ-Definition
The electron transport chain (ETC) is the τ-categorical oxidoreductase cascade that converts the reducing power of NADH and FADH₂ into a proton gradient. Categorically, it is the upstream half of oxidative phosphorylation: a series of four membrane-embedded complexes (I-IV) that move electrons stepwise toward O₂, releasing free energy in pump-sized increments and transducing it into transmembrane H⁺ flux.
Categorical invariant. Stepwise electron-transfer cascade with redox potentials traversing E°' ≈ -320 mV (NADH) → +820 mV (O₂/H₂O), Δ ≈ 1.14 V; pumps 10 H⁺ per NADH oxidized (Complex I: 4, III: 4, IV: 2) on the cytochrome-c branch.
Primary registry anchor:
VI.D32
τ-Derivation Chain
Empirical Correlate
Biomarker: Complex stoichiometry per NADH: 4 H⁺ (I) + 4 H⁺ (III) + 2 H⁺ (IV) = 10 H⁺ pumped; redox span E°' = -320 mV (NADH/NAD⁺) to +820 mV (O₂/H₂O); ubiquinone pool [Q]_total ≈ 5-10 mM in inner membrane; cytochrome-c content ~0.5 mM; ROS leak rate ~1-3% of electron flux at Complexes I and III.
Measurable range: Complex I activity 100-500 nmol NADH min⁻¹ mg⁻¹ protein; Complex IV (cytochrome c oxidase) turnover ~250 s⁻¹ per heme a₃; ETC supercomplex (I+III₂+IV, the 'respirasome') visible by blue-native PAGE and cryo-EM; full chain electron transit time ≈10 ms per electron pair.
Observation method: Blue-native PAGE for complex assembly, in-gel activity stains, spectrophotometric assays of individual complexes (Complex I: NADH:ubiquinone reductase at 340 nm; IV: reduced-cytochrome-c oxidation at 550 nm), Oroboros high-resolution respirometry with sequential substrate / inhibitor titration, cryo-EM of supercomplexes.
Calibration anchor: LG-Y02-kinetic-pseudoscalar-channel
Anchor chain:
- VI.L18 chirality channel
- iron-sulfur cluster handedness in Complexes I, II, III
- stereospecific orientation of every embedded oxidoreductase across the bilayer
Manuscript reference: manuscript-sources/book-06/part03/ch20-atp.tex
Lean Coverage
Status: Planned