31–35 — CONSERVED ENERGETIC STATES
These should not all be called one interchangeable “currency.” They perform different functions.
Operational definition
Layer type: Immediate energetic-state layer Governs: Items 31–35
Formal definition
The Conserved Energetic States layer identifies the nonequilibrium molecular or electrochemical conditions in which recently captured free energy or reducing capacity is temporarily held and made available for coupled biological work.
Governing question
In what immediately usable physical or chemical form is the captured capacity for work retained?
Included state classes
- electrochemical ion potential;
- phosphoryl-transfer potential;
- reducing power;
- activated-group transfer potential;
- rapid cellular energetic buffers.
Inclusion rule
A state belongs here when it can drive an otherwise unfavorable process through a defined coupling mechanism.
Examples include:
- an ion gradient driving ATP synthesis or transport;
- ATP hydrolysis driving biosynthesis;
- NADPH donating electrons to reductive synthesis;
- an activated thioester driving acyl transfer;
- phosphocreatine buffering ATP demand.
State-versus-molecule distinction
The energetic property does not reside in a molecule independently of its surroundings.
The useful capacity depends upon:
- concentrations of reactants and products;
- redox ratios;
- membrane voltage;
- ion distributions;
- pH;
- compartmentation;
- enzyme coupling;
- temperature and pressure.
Therefore the layer classifies energetic states and potentials, not merely a list of “energy molecules.”
Distinction from storage
These states generally turn over rapidly.
They are not equivalent to bulk reserves such as:
- fat;
- glycogen;
- starch;
- seed oil;
- cached food.
Immediate energetic states carry active metabolic flux. Storage pools preserve surplus across longer mismatches between acquisition and demand.
31. Electrochemical potential
- proton motive force
- sodium motive force
- membrane potential
- chemical ion gradients
32. Phosphoryl-transfer potential
- ATP
- GTP
- other nucleoside triphosphates
- pyrophosphate
33. Reducing power
- NADH
- NADPH
- reduced ferredoxin
- FAD-associated reducing equivalents
- flavodoxin
- reduced coenzyme F₄₂₀
- other specialized carriers
34. Activated-group transfer potential
- acetyl-CoA and other thioesters
- phosphoenolpyruvate
- acyl phosphates
- activated sugars
- activated amino-acid intermediates
35. Rapid cellular energy buffers
- phosphocreatine
- phosphoarginine
- other phosphagens
- rapidly reversible ion or redox pools