Enantiostasis is the ability of an open system, especially a living

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

, to maintain and conserve its metabolic and physiological functions in response to variations in an unstable environment. Estuarine organisms typically undergo enantiostasis in order to survive with constantly changing salt concentrations. The Australian NSW Board of Studies defines the term in its Biology syllabus as "the maintenance of metabolic and physiological functions in response to variations in the environment". Enantiostasis is not a form of classical

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

, meaning "standing at a similar level," which focuses on maintenance of internal body conditions such as pH, oxygen levels, and ion concentrations. Rather than maintaining homeostatic (stable ideal) conditions, enantiostasis involves maintaining only functionality in spite of external fluctuations. However, it can be considered a type of homeostasis in a broader context because functions are kept relatively consistent. Organic compounds such as

Taurine Taurine (), or 2-aminoethanesulfonic acid, is an organic compound that is widely distributed in animal tissues. It is a major constituent of bile and can be found in the large intestine, and accounts for up to 0.1% of total human body weight. It ...

have been shown to still properly function within environments that have been disrupted from an ideal state. The term ''enantiostasis'' was proposed by Mangum and Towle. It is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

('; opposite, opposing, over against) and ('; to stand, posture).

Trehalose

* Fruit Flies Drosophila use the non-toxic sugar trehalose that is found in the hemolymph of insects to cope with changes in environmental conditions. Trehalose levels can spike up to 2% in the hemolymph in response to temperature changes, salinity and osmotic and oxidative stress. * Yeast cells accumulate Trehalose in order to withstand heat stress.

Estuarine Environments

Examples of organisms which undergo enantiostasis in an estuarine environment include: * The oxygen binding effectiveness of

hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2) ...

in the blue crab ''

Callinectes sapidus ''Callinectes sapidus'' (from the Ancient Greek ,"beautiful" + , "swimmer", and Latin , "savory"), the blue crab, Atlantic blue crab, or regionally as the Chesapeake blue crab, is a species of crab native to the waters of the western Atlantic O ...

'' varies according to the concentration of two factors, calcium ion concentration, and hydrogen ion concentration. When these concentrations are varied in the same direction, they have a counterbalancing effect. To stabilize oxygen binding at low ionic concentrations, the crab increases its internal pH (decreasing the hydrogen ion concentration) to allow the hemocyanin to continue to function efficiently. * The

Dungeness crab The Dungeness crab (''Metacarcinus magister'') is a species of crab inhabiting eelgrass beds and water bottoms along the west coast of North America. It typically grows to across the carapace and is a popular seafood. Its common name comes from ...

, ''Cancer magister'', relies on the magnesium ion (Mg2+) for its

oxygen affinity. In the juvenile stage, the crab has higher magnesium ion concentrations resulting in higher hemocyanin oxygen affinity. This changes throughout development, such that the adult ''Cancer magister'' has less magnesium ion and thus, less hemocyanin oxygen affinity. Intrinsic oxygen affinity is inversely proportional magnesium ion concentrations in the crab, which counterbalances the hemocyanin oxygen affinity.

High Salt Environments

Halophiles The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...

have adapted to high salt environments by using energy from the sun to maintain a high internal potassium ion concentration and by using biological proteins that can function in the varying, high internal potassium ion concentrations. These adaptions allow halophiles to thrive by increasing internal osmolarity to compensate for the high sodium concentrations of the external environment, which prevents the movement of water out of the cell.

References

{{reflist Ecology Homeostasis