Deasy’s Taxonomia Vitae – ENERGY-CONSERVATION MECHANISM

Operational definition

Layer type: Coupling-mechanism layer Governs: Items 24–30

Governing question

By what mechanism is released free energy prevented from being immediately lost as heat?

Included mechanisms

• membrane-based chemiosmosis;
• electron-transport phosphorylation;
• substrate-level phosphorylation;
• electron bifurcation;
• electron confurcation;
• reverse electron transport;
• other ion-coupled conservation systems.

Required components

A complete mechanism description should identify:

1. the exergonic driving process;
2. the coupling machinery;
3. the endergonic process being driven;
4. the conserved energetic product;
5. the membrane or compartment, where relevant.

Example

electron transfer
→
proton translocation
→
proton motive force
→
ATP synthase
→
ATP

Experimental studies directly demonstrate proton-motive-force-driven ATP synthesis and the dependence of ATP synthase activity on the electrochemical driving force. (PubMed Central (PMC))

Inclusion rule

A process belongs here only if it couples a favorable transformation to the production of a usable energetic state or to the execution of an otherwise unfavorable reaction.

Exclusion rule

This layer excludes:

• the original environmental source;
• the electron donor’s identity;
• the conserved energetic state itself;
• long-term storage;
• the final biological function.

A proton gradient is a state. Proton pumping is a conservation mechanism.

24. Membrane-based chemiosmosis

24.1 Proton motive force

Δ p=Δψ-(2.303RT / F)Δ pH

Its components are:

• electrical membrane potential
• chemical proton gradient

24.2 Sodium motive force

A sodium electrochemical gradient drives:

• ATP production
• transport
• motility
• other cellular work

24.3 Mixed ion systems

Some organisms use both proton- and sodium-coupled systems.

24.4 ATP synthase coupling

ion motive force → ATP synthase rotation → ATP

Proton motive force and sodium motive force are therefore conserved intracellular energetic states, not equivalent primary environmental trophic sources. (PubMed Central (PMC))

25. Electron-transport phosphorylation

25.1 Oxidative phosphorylation

Respiratory electron transport produces an ion gradient that drives ATP synthesis.

25.2 Photophosphorylation

Light-driven electron transport or ion pumping produces the gradient.

25.3 Extracellular respiratory phosphorylation

External solid or electrode-associated electron transfer supports membrane energy conservation.

26. Substrate-level phosphorylation

A high-transfer-potential intermediate directly phosphorylates:

ADP → ATP

or an equivalent nucleotide diphosphate.

27. Electron bifurcation

One pair of electrons is divided so that:

• one transfer proceeds favorably
• the released free energy drives a second, unfavorable reduction

28. Electron confurcation

Two electron flows are combined to drive a common reduction.

Electron bifurcation and confurcation are especially important in anaerobic microbial bioenergetics and expand the taxonomy beyond the simplified “respiration versus fermentation” distinction. (PubMed Central (PMC))

29. Reverse electron transport

Previously conserved energy is spent to drive electrons toward a more reducing potential.

Purpose:

• generate NADH
• generate NADPH
• reduce ferredoxin
• support carbon fixation or biosynthesis

30. Other ion-coupled conservation mechanisms

• ion-translocating decarboxylation
• methyl-transfer-linked ion translocation
• pyrophosphate-driven pumps
• specialized archaeal energy-conserving systems