Vanadium bromoperoxidases are a kind of

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 ...

s called haloperoxidases. Its primary function is to remove

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 ...

which is produced during

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

from in or around the cell. By producing

hypobromous acid Hypobromous acid is a weak, unstable acid with chemical formula of HOBr. It is mainly produced and handled in an aqueous solution. It is generated both biologically and commercially as a disinfectant. Salts of hypobromite are rarely isolated as ...

(HOBr) a secondary reaction with

dissolved organic matter Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called parti ...

, what results is the

bromination In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymer ...

of organic compounds that are associated with the defense of the organism. These enzymes produce the bulk of natural organobromine compounds in the world. Vanadium bromoperoxidases are one of the few classes of enzymes that requires

vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer ( pass ...

. The active site features a vanadium oxide center attached to the protein via one histidine side chain and a collection of

hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...

s to the oxide ligands.

Occurrence and function

Vanadium bromoperoxidases have been found in bacteria, fungi, marine macro algae ( seaweeds), and marine microalgae (

diatoms A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

) which produce brominated organic compounds. It has not been definitively identified as the bromoperoxidase of higher eukaryotes, such as

murex ''Murex'' is a genus of medium to large sized predatory tropical sea snails. These are carnivorous marine gastropod molluscs in the family Muricidae, commonly called "murexes" or "rock snails".Houart, R.; Gofas, S. (2010). Murex Linnaeus, 175 ...

snails, which have a very stable and specific bromoperoxidase, but perhaps not a vanadium dependent one. While the purpose of the bromoperoxidase is still unknown, the leading theories include that it’s a way of regulating hydrogen peroxide produced by photosynthesis and/or as a self-defense mechanism by producing hypobromic acid which prevents the growth of bacteria. The enzymes catalyse the oxidation of bromide (0.0067% of

sea water Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approx ...

) by

. The resulting electrophilic bromonium cation (Br⁺) attacks hydrocarbons (symbolized as R-H in the following equation): :R-H + Br⁻ + H₂O₂ → R-Br + H₂O + OH⁻ The bromination acts on a variety of dissolved organic matter and increasingly bromination leads to the formation of

bromoform Bromoform (CHBr3) is a brominated organic solvent, colorless liquid at room temperature, with a high refractive index, very high density, and sweet odor is similar to that of chloroform. It is one of the four haloforms, the others being fluoroform, ...

. The vanadium bromoperoxidases produce an estimated 1–2 million tons of

and 56,000 tons of

bromomethane Bromomethane, commonly known as methyl bromide, is an organobromine compound with formula C H3 Br. This colorless, odorless, nonflammable gas is produced both industrially and biologically. It has a tetrahedral shape and it is a recognized ozo ...

annually. Partially in the polar regions, which has high blooms of microalgae in the spring, these compounds have the potential to enter the troposphere and lower stratosphere. Through

photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...

, brominated methanes produce a bromine radical (Br^.) that can lead to ozone depletion. Most of the earth's natural

organobromine compound Organobromine compounds, also called organobromides, are organic compounds that contain carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons avai ...

s arise by the action of this enzyme.

References

External links

* * Example structure: * Family/Domain classifications: ** ** ** ** EC 1.11.1 {{Enzyme-stub