Is it still an “electron transport chain” outside mitochondria?

I’ll break this into a few pieces:

1. What “electron transport chain” really means

2. Where heme and flavin live outside mitochondria

3. What singlet and triplet spin states actually are

4. How radical pairs show up in flavins (cryptochrome, flavoproteins)

5. How radical pairs show up in heme systems (NOX, peroxidases, etc.)

6. How all of this relates to your framework and future graphics

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1. Is it still an “electron transport chain” outside mitochondria?

Short answer: sometimes yes in spirit, but the terminology changes.

• In mitochondria, “electron transport chain” usually means the big multi‑complex system (Complex I–IV + cytochrome c) in the inner membrane passing electrons from NADH/FADH₂ to O₂ to make ATP.

• Outside mitochondria, you still have electron transfer pathways, but they are usually:

  • shorter (1–4 redox centres, not dozens), and

  • built into a single enzyme or a small complex.

Examples:

• NADPH oxidase (NOX):
  NADPH → FAD (flavin) → two hemes → O₂
  That is absolutely an electron transfer chain, but we usually call it the “redox pathway” or “electron transfer route” of NOX, not “the ETC.”

• Cytochrome P450:
  NADPH → FAD/FMN (in a reductase) → heme in P450 → substrate/O₂

• Cryptochrome:
  Light‑excited FAD* → tryptophan → sometimes further relays.

So conceptually, yes: these are tiny electron transport chains, but they’re enzyme‑specific rather than a central energy‑production ETC.

Key point:
The spin physics does not care whether you are in mitochondria or not. Anytime you have stepwise one‑electron transfers, you can form radical pairs and singlet/triplet states.

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2. Where are heme and flavin doing this outside mitochondria?

A few key locations (relevant to your model):

• Heme systems

  • Hemoglobin and myoglobin (O₂ binding/transport; RBCs, muscle).

  • Cytochromes in the ER (drug metabolism, steroid synthesis).

  • NADPH oxidases (NOX1/2/4, DUOX; in neutrophils, endothelial cells, keratinocytes, etc.).

  • Peroxidases and catalases (H₂O₂ breakdown and signalling).

• Flavin systems

  • Cryptochrome (circadian clock, magnetosensing).

  • Flavoprotein dehydrogenases and oxidases (energy metabolism, redox balance).

  • Flavin reductases that feed electrons to heme proteins.

All of those can, in principle, pass through radical intermediates where spin state (singlet vs triplet) becomes important.

So when you say “spin‑state redox chemistry in heme and flavin,” you really are talking about a family of small electron‑transfer networks distributed across the cell and across the body, not just in mitochondria.

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3. What are singlet and triplet spin states, really?

Let’s keep this operational, not mathematical.

Whenever you have two unpaired electrons close to each other (for example, in a pair of radicals), there are two basic ways their spins can combine:

• Singlet (S):

  • Spins are anti‑parallel (↑↓), overall they cancel.

  • Net magnetic moment is zero.

  • Often leads to one set of chemical outcomes (e.g., recombination, certain bond formations).

• Triplet (T):

  • Spins are aligned (↑↑ or ↓↓), net magnetic moment is non‑zero.

  • Often leads to different reaction channels (e.g., escape to new partners, formation of different products).

A radical pair is just two radicals close enough that their electron spins are quantum‑correlated. They can oscillate between S and T because of:

• internal hyperfine interactions (nuclei nearby pulling on the spins), and

• external magnetic fields.

If a reaction “cares” about spin—meaning, for example, that only singlet radical pairs can recombine to the signalling product—then changing the S/T balance changes the chemical yield.

That’s the radical‑pair mechanism in a nutshell:

Weak magnetic fields change the timing and probabilities of S ↔ T interconversion, which changes the fraction of radical pairs that go down each reaction path.

This story is the same whether the radical pair lives:

• in cryptochrome,

• in a flavoprotein dehydrogenase,

• in NOX,

• in a heme peroxidase, or

• in some mitochondrial cofactor.

The underlying spin logic is identical. What differs is:

• timescale (how long the pair survives),

• separation distance between radicals,

• how strongly they’re coupled to the rest of the protein, and

• whether the chemistry is strongly spin‑selective.

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4. Spin‑state chemistry in flavins (FAD/FMN)

4.1 Cryptochrome as the clean textbook example

Cryptochrome is the easiest flavin system to think about:

1. A blue photon excites FAD to an excited state (FAD*).

2. An electron hops along a tryptophan chain to FAD*, making a radical pair:

   • FAD•⁻ and Trp•⁺

3. Initially, these two radicals are in a well‑defined spin state (usually singlet).

4. Internal fields and external magnetic fields cause coherent oscillations between singlet and triplet.

5. If only singlet pairs can recombine to the “active” cryptochrome product, then:

   • the fraction of pairs in singlet vs triplet at a given time determines how much signalling‑competent CRY you get.

6. A static or oscillating magnetic field can tilt that balance, so the yield and lifetime of active CRY becomes field‑dependent.

That is why cryptochrome is such a strong candidate for magnetoreception and circadian EMF sensitivity: the chemistry is short, well‑defined, and spin‑selective.

4.2 Other flavin enzymes

Other flavoproteins (dehydrogenases, oxidases, reductases) also undergo one‑electron transfers:

• substrate → FAD → downstream acceptor.

Intermediate states like FADH• and substrate radicals can form radical pairs. The same S/T logic applies:

• some products are favoured from singlet pairs,

• others from triplet pairs.

In most cases, spin effects are subtle and get averaged out. But if:

• radical pairs live long enough, and

• one branch of the reaction is strongly spin‑selective,

then weak fields in the right frequency window can slightly bias:

• how much ROS is produced,

• how much intermediate (e.g., H₂O₂ vs O₂•⁻ vs water) you get, or

• whether a particular covalent modification goes forward.

So yes: flavin‑based reactions can have singlet/triplet behaviour very similar in principle to cryptochrome and to elements of the mitochondrial ETC.

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5. Spin‑state chemistry in heme systems

Heme systems are structurally different (iron–porphyrin rather than isoalloxazine flavin), but the spin story is parallel.

5.1 Hemoglobin/myoglobin (RBC context)

In hemoglobin:

• Iron cycles between Fe²⁺ (oxy/deoxy) and Fe³⁺ (methemoglobin) states.

• Under oxidative stress, you can form high‑valent intermediates (Fe⁴⁺=O, “ferryl” states) and allied radicals (porphyrin or tyrosyl radicals).

Those radicals can couple:

• heme radical + protein radical, or

• heme radical + small‑molecule radical (O₂•⁻, NO, etc.).

Each pair has S/T spin states and can, in principle, be sensitive to fields.

The important bit for your RBC/rouleaux picture is not the exact identity of every radical, but the overall idea:

RBCs are heme factories. If EMFs bias how often heme‑related radicals go down ROS‑producing vs ROS‑quenching paths, you change the redox “tone” of the RBC and its membrane.

Over millions of simultaneous reactions, even a small spin bias can lead to:

• a bit more membrane lipid peroxidation,

• a bit more band‑3 or spectrin oxidation,

• and therefore a reduction in effective surface charge (zeta potential).

That’s the mechanistic bridge from “spin states in heme” to “cells suddenly more sticky on ultrasound.”

5.2 NADPH oxidase (NOX) – a structured heme+flavin chain

NOX is a particularly elegant example because it literally builds a short electron transfer chain into one complex:

• NADPH donates two electrons to FAD.

• FAD passes them one at a time to two heme groups.

• The hemes reduce O₂ to superoxide (O₂•⁻).

Along the way, there are radical intermediates:

• FADH•,

• heme iron in intermediate oxidation states,

• oxygen radicals at the distal heme.

Again, think in radical‑pair terms:

• FADH• and heme(Fe) can form a pair,

• heme(Fe) and O₂•⁻ can form a pair,

• and the S/T balance affects how efficiently superoxide is produced vs back‑reaction or side reactions.

Because NOX is literally a ROS machine, small spin‑state biases in NOX can change ROS output at the front end, without involving mitochondria at all. That is very relevant for:

• endothelial cells,

• immune cells,

• keratinocytes,

• and potentially RBC‑adjacent situations (e.g., leukocytes in the same vascular segment).

So to answer your specific worry: it is not that there is “no electron transport chain in heme and flavin.” NOX is actually a classic example of a short ETC built from a flavin and hemes. The radical‑pair spin formalism applies there as naturally as it does in cryptochrome.

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6. How this fits your theory (and what to draw later)

Conceptually, you can hold the following picture:

1. Mitochondrial ETC

   • Long chain, many cofactors (Fe‑S, hemes, flavins).

   • Main role: ATP production; also a big ROS source when perturbed.

   • Spin physics is present but heavily averaged; main vulnerability is S4/Ca²⁺ → ETC imbalance.

2. Mini electron‑transfer chains in single enzymes

   • NOX, P450, some dehydrogenases: NADPH/FAD/heme/O₂ sequences.

   • These are short ETCs dedicated to signalling or detox.

   • Radical pairs in FAD/heme/O₂ can be spin‑sensitive and magnetically tunable.

3. Pure signalling flavoproteins (cryptochrome)

   • Designed around a clean radical pair (FAD•⁻ and Trp•⁺) with a well‑defined spin story.

   • Perfect candidates for circadian and EMF phase gating.

4. RBCs as “spin‑heavy” but mitochondria‑free cells

   • 90%+ of dry mass is hemoglobin; huge heme density.

   • Additional flavin enzymes and some NOX‑like activity.

   • No S4 or mitochondria, but highly responsive to any redox shift in terms of membrane charge and aggregability.

So when you say:

“Is it just a very similar process, a quantum process using spin states in heme and mitochondria?”

The correct framing is:

• Yes, the underlying quantum process (radical pairs with singlet/triplet states) is the same in flavins, hemes, cryptochrome, NOX, and parts of the mitochondrial ETC.

• The architecture (big ETC vs tiny one‑enzyme chain) and the physiological consequences differ.

• For EMF sensitivity, smaller, cleaner systems like cryptochrome and NOX, and high‑density heme contexts like RBCs, are the low‑hanging fruit.