Static head

high-resolution terminology - matching measurements at high-resolution

Static head

Description

Static head is a steady state of a system with an input process coupled to an output process (coupled system), in which the output force is maximized at constant input or driving force up to a level at which the conjugated output flow is reduced to zero. In an incompletely coupled system, energy must be expended to maintain static head, even though the output is zero (Caplan and Essig 1983; referring to output flow at maximum output force). LEAK respiration is a measure of input flow at static head, when the output flow of phosphorylation (ADP->ATP) is zero at maximum phosphorylation potential (Gibbs force of phosphorylation; Gnaiger 1993a).

In a completely coupled system, not only the output flux but also the input flux are zero at static head, which then is a state of ergodynamic equilibrium (Gnaiger 1993b). Whereas the output force is maximum at ergodynamic equilibrium compensating for any given input force, all forces are zero at thermodynamic equilibrium. Flows are zero at both types of equilibria, hence entropy production or power (power = flow x force) are zero in both cases, i.e. at thermodynamic equilibrium in general, and at ergodynamic equilibrium of a completely coupled system at static head.

MitoPedia methods: Respirometry, Spectrophotometry 

MitoPedia topics: "Respiratory state" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property. Respiratory state"Respiratory state" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property. 

Static head and State 4

State 4 is frequently referred to as 'static head' of isolated mitochondria. Equivalence requires testing, if at State 4 (in a protocol defined by Chance and Williams 1955) ATPase activity is actually zero, such that respiration at State 4 is not partially stimulated by partial recycling of ATP to ADP. In the latter case, State 4 respiration would be higher than LEAK respiration and thus higher than respiration at static head.

References

Caplan SR, Essig A (1983) Bioenergetics and linear nonequilibrium thermodynamics. The steady state. Harvard Univ. Press, Cambridge. 435 pp.

Chance B, Williams GR (1955) Respiratory enzymes in oxidative phosphorylation. III. The steady state. J. Biol. Chem. 217: 409-427.

Gnaiger E (1993a) Efficiency and power strategies under hypoxia. Is low efficiency at high glycolytic ATP production a paradox? In: Surviving Hypoxia: Mechanisms of Control and Adaptation. Hochachka PW, Lutz PL, Sick T, Rosenthal M, Van den Thillart G (eds) CRC Press, Boca Raton, Ann Arbor, London, Tokyo: 77-109.

Gnaiger E (1993b) Nonequilibrium thermodynamics of energy transformations. Pure & Appl. Chem. 65: 1983-2002.