Extracellular superoxide dismutase u-Zn'' is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

that in

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s is encoded by the ''SOD3''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

. This gene encodes a member of the

superoxide dismutase Superoxide dismutase (SOD, ) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide () radical into ordinary molecular oxygen (O2) and hydrogen peroxide (). Superoxide is produced as a by-product of oxygen me ...

(SOD) protein family. SODs are

antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...

s that

catalyze Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

the

dismutation In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...

of two

superoxide In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the ...

radicals into

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

. The product of this gene is thought to protect the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...

, and other tissues from

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily Detoxification, detoxify the reactive intermediates or to repair the resulting damage. Disturbances ...

. The protein is secreted into the

extracellular space Extracellular space refers to the part of a multicellular organism outside the cells, usually taken to be outside the plasma membranes, and occupied by fluid. This is distinguished from intracellular space, which is inside the cells. The compositi ...

and forms a

glycosylated Glycosylation is the reaction in which a carbohydrate (or 'glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not alw ...

homotetramer A tetrameric protein is a protein with a protein quaternary structure, quaternary structure of four subunits (tetrameric). Homotetramers have four identical Protein subunit, subunits (such as glutathione S-transferase), and heterotetramers are M ...

that is anchored to the

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...

(ECM) and cell surfaces through an interaction with

heparan sulfate Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan (HSPG, i.e. Heparan Sulfate ProteoGlycan) in which two or three HS chains are attached in close proximity to cell surface or extracellular ma ...

proteoglycan Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to whic ...

and

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...

. A fraction of the protein is cleaved near the

C-terminus The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

before secretion to generate circulating tetramers that do not interact with the ECM. Among

black garden ant The black garden ant (''Lasius niger''), also known as the common black ant, is a formicine ant, the type species of the subgenus ''Lasius'', which is found across Europe and in some parts of North America, South America, Asia and Australasia. ...

s (''Lasius niger''), the lifespan of

queens Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. Located on Long Island, it is the largest New York City borough by area. It is bordered by the borough of Brooklyn at the western tip of Long ...

is an order of magnitude greater than of workers despite no systematic nucleotide sequence difference between them.Lucas ER, Keller L. Elevated expression of ageing and immunity genes in queens of the black garden ant. Exp Gerontol. 2018 Jul 15;108:92-98. doi: 10.1016/j.exger.2018.03.020. Epub 2018 Apr 3. PMID: 29625209 The ''SOD3'' gene was found to be the most differentially over-expressed gene in the brains of queen vs worker ants. This finding raises the possibility that SOD3 antioxidant activity plays a key role in the striking longevity of social insect queens.

References

Further reading