Description

Mitochondrial markers are structural or functional properties that are specific for mitochondria. A structural mt-marker is the area of the inner mt-membrane or mt-volume determined stereologically, which has its limitations due to different states of swelling. If mt-area is determined by electron microscopy, the statistical challenge has to be met to convert area into a volume. When fluorescent dyes are used as mt-marker, distinction is necessary between mt-membrane potential dependent and independent dyes. mtDNA or cardiolipin content may be considered as a mt-marker. Mitochondrial marker enzymes may be determined as molecular (amount of protein) or functional properties (enzyme activities). Respiratory capacity in a defined respiratory state of a mt-preparation can be considered as a functional mt-marker, in which case respiration in other respiratory states is expressed as flux control ratios. » MiPNet article

Abbreviation: mt-marker

Reference: Gnaiger 2020 BEC MitoPathways

Mitochondrial markers and expression of mitochondrial respiration

Gnaiger E (2014) Mitochondrial markers and expression of mitochondrial respiration. Mitochondr Physiol Network 2014-07-26.

Oroboros (2014) MiPNet

Abstract: Respiratory performance capacity of an organism, tissue or cell may change due to a change in size, concentration of functional elements (biomarker density) or element function (mt-specific function).

• O2k-Network Lab: AT Innsbruck Gnaiger E

Biomarkers

Oxygen flow and normalized flux in living cells. From Gnaiger 2020 BEC MitoPathways.

Markers for size are volume, mass, area. If mass is not expressed as total mass but as protein mass, then a physical marker of size is replaced by a biochemical marker. In isolated mitochondria, protein can be determined as a measure of amount of mitochondria or mt-concentration [mg mt-protein/mL]. However, protein cannot be used as a mt-biomarker in other mitochondrial preparations.

Determination of the size of a system under investigation always requires the definition of the system. The system (subject) whose phenotype is studied may be an organism, a tissue, or a cell. The biochemical marker total protein can be replaced by a specific protein, e.g. by a marker enzyme (Renner et al 2003). A biomarker can be considered as a functional element. Expressing performance (I_O2, oxygen flow per biological system) per size yields specific performance (J_O2, oxygen flux = flow per system size) in an unstructured analysis (Gnaiger 1993).

A biomarker introduces a structural (and functional) element into the analysis. Therefore, expressing performance (I_O2) per functional element mtE (biomarker) yields marker-specific performance (J_O2/mtE, mt-specific oxygen flux per mt-marker) in a structured analysis (Gnaiger 2020).

When replacing an enzyme activity by the respiratory activity in a defined respiratory state as a biomarker, then flow per mt-marker becomes a flux control ratio FCR (Gnaiger 2009; Pesta et al 2011). Expressing structure by functional markers is without problem as long as the structure in question does not undergo any functional (qualitative) changes.

References

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Gnaiger 1993 Pure Appl Chem	Gnaiger E (1993) Nonequilibrium thermodynamics of energy transformations. Pure Appl Chem 65:1983-2002. http://dx.doi.org/10.1351/pac199365091983	1993
Gnaiger 2009 Int J Biochem Cell Biol	Gnaiger E (2009) Capacity of oxidative phosphorylation in human skeletal muscle. New perspectives of mitochondrial physiology. Int J Biochem Cell Biol 41:1837-45. https://doi.org/10.1016/j.biocel.2009.03.013	2009
Gnaiger 2020 BEC MitoPathways	Gnaiger E (2020) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5^th ed. Bioenerg Commun 2020.2. https://doi.org/10.26124/bec:2020-0002	2020
BEC 2020.1 doi10.26124bec2020-0001.v1	Gnaiger E et al ― MitoEAGLE Task Group (2020) Mitochondrial physiology. Bioenerg Commun 2020.1. https://doi.org/10.26124/bec:2020-0001.v1	2020
Pesta 2011 Am J Physiol Regul Integr Comp Physiol	Pesta D, Hoppel F, Macek C, Messner H, Faulhaber M, Kobel C, Parson W, Burtscher M, Schocke M, Gnaiger E (2011) Similar qualitative and quantitative changes of mitochondrial respiration following strength and endurance training in normoxia and hypoxia in sedentary humans. Am J Physiol Regul Integr Comp Physiol 301:R1078–87.	2011
Renner 2003 Biochim Biophys Acta	Renner K, Amberger A, Konwalinka G, Gnaiger E (2003) Changes of mitochondrial respiration, mitochondrial content and cell size after induction of apoptosis in leukemia cells. Biochim Biophys Acta 1642:115-23.	2003