Haloperoxidase
Encyclopedia
Haloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide
. Both halides and hydrogen peroxide are widely available in the environment
.
The Nernst equation
shows that hydrogen peroxide can oxidize chloride
(E°= 1.36 V), bromide
(E°= 1.09 V) and iodide
(E°= 0.536 V) from a thermodynamic perspective under natural conditions, i.e., a temperature range of about 0-30 °C and a pH
ranging from about 3 (humic soil layer) to about 8 (sea water). Fluoride
(E°= 2.87 V) cannot be oxidized by hydrogen peroxide. The table shows the classification of haloperoxidases according to the halides whose oxidation they are able to catalyze.
The classification of these enzymes by substrate-usability does not necessarily indicate enzyme substrate preference. For example, although eosinophil peroxidase
is able to oxidize chloride, it preferentially oxidizes bromide.
The mammalian haloperoxidases myeloperoxidase (MPO), lactoperoxidase (LPO,) and eosoniphil peroxidase (EPO) are also capable of oxidizing the pseudohalide thiocyanate
(SCN-). They each contain a heme
prosthetic group covalently bound by two ester linkages to aspartate and/or glutamate side-chains. MPO has a third covalent link through a methionine
residue. Horseradish peroxidase
is also capable of oxidizing these substrates, but its heme is not covalently bound and becomes damaged during turnover.
A specific vanadium bromoperoxidase
in marine organisms (fungi, bacteria, microalgae, perhaps other eukaryotes) uses vanadate
and hydrogen peroxide to brominate electrophilic organics.
Murex
snails have a bromoperoxidase
used to produce Tyrian purple
dye. The enzyme is very specific to bromide and physically stable, but has not been characterized as to its active site.
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
. Both halides and hydrogen peroxide are widely available in the environment
Environment (biophysical)
The biophysical environment is the combined modeling of the physical environment and the biological life forms within the environment, and includes all variables, parameters as well as conditions and modes inside the Earth's biosphere. The biophysical environment can be divided into two categories:...
.
The Nernst equation
Nernst equation
In electrochemistry, the Nernst equation is an equation that can be used to determine the equilibrium reduction potential of a half-cell in an electrochemical cell. It can also be used to determine the total voltage for a full electrochemical cell...
shows that hydrogen peroxide can oxidize chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
(E°= 1.36 V), bromide
Bromide
A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...
(E°= 1.09 V) and iodide
Iodide
An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
(E°= 0.536 V) from a thermodynamic perspective under natural conditions, i.e., a temperature range of about 0-30 °C and a pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
ranging from about 3 (humic soil layer) to about 8 (sea water). Fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
(E°= 2.87 V) cannot be oxidized by hydrogen peroxide. The table shows the classification of haloperoxidases according to the halides whose oxidation they are able to catalyze.
The classification of these enzymes by substrate-usability does not necessarily indicate enzyme substrate preference. For example, although eosinophil peroxidase
Eosinophil peroxidase
Eosinophil peroxidase is a haloperoxidase enzyme that in humans is encoded by the EPX gene. The enzyme is a heterodimeric 71-77 kD peroxidase consisting of a heavier glycosylated chain and a lighter nonglycosylated chain...
is able to oxidize chloride, it preferentially oxidizes bromide.
The mammalian haloperoxidases myeloperoxidase (MPO), lactoperoxidase (LPO,) and eosoniphil peroxidase (EPO) are also capable of oxidizing the pseudohalide thiocyanate
Thiocyanate
Thiocyanate is the anion [SCN]−. It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Organic compounds containing the functional group SCN are also called thiocyanates...
(SCN-). They each contain a heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
prosthetic group covalently bound by two ester linkages to aspartate and/or glutamate side-chains. MPO has a third covalent link through a methionine
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...
residue. Horseradish peroxidase
Horseradish peroxidase
The enzyme horseradish peroxidase , found in horseradish, is used extensively in biochemistry applications primarily for its ability to amplify a weak signal and increase detectability of a target molecule.-Applications:...
is also capable of oxidizing these substrates, but its heme is not covalently bound and becomes damaged during turnover.
A specific vanadium bromoperoxidase
Vanadium bromoperoxidase
Vanadium bromoperoxidase is a haloperoxidase, used to synthesize halogenated organic compounds associated with defense and pigmentation in seaweeds and marine algae. It is the source of the bulk of organobromine compounds in the ocean...
in marine organisms (fungi, bacteria, microalgae, perhaps other eukaryotes) uses vanadate
Vanadate
In chemistry, a vanadate is a compound containing an oxoanion of vanadium generally in its highest oxidation state of +5. The simplest vanadate ion is the tetrahedral, orthovanadate, VO43− anion, which is present in e.g. sodium orthovanadate and in solutions of V2O5 in strong base...
and hydrogen peroxide to brominate electrophilic organics.
Murex
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 calle "murexes" or "rock snails"...
snails have a bromoperoxidase
Bromoperoxidase
Bromoperoxidases are enzymes that catalyse the bromination of hydrocarbons. The enzymes accomplish this reaction via the following reaction:Related chloroperoxidase enzymes effect chlorination....
used to produce Tyrian purple
Tyrian purple
Tyrian purple , also known as royal purple, imperial purple or imperial dye, is a purple-red natural dye, which is extracted from sea snails, and which was possibly first produced by the ancient Phoenicians...
dye. The enzyme is very specific to bromide and physically stable, but has not been characterized as to its active site.
| Haloperoxidase | Oxidisable halide | Origin |
|---|---|---|
| Chloroperoxidase (CPO) | Cl–, Br–, I– | neutrophils (myeloperoxidase Myeloperoxidase Myeloperoxidase is a peroxidase enzyme that in humans is encoded by the MPO gene. Myeloperoxidase is most abundantly expressed in neutrophil granulocytes . It is a lysosomal protein stored in azurophilic granules of the neutrophil... ), eosinophils (eosinophil peroxidase Eosinophil peroxidase Eosinophil peroxidase is a haloperoxidase enzyme that in humans is encoded by the EPX gene. The enzyme is a heterodimeric 71-77 kD peroxidase consisting of a heavier glycosylated chain and a lighter nonglycosylated chain... ), Caldariomyces fumago |
| Bromoperoxidase (BPO) | Br–, I– | milk Milk Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many... , saliva Saliva Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,... , tears Tears Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears.... (lactoperoxidase Lactoperoxidase Lactoperoxidase is a peroxidase enzyme secreted from mammary, salivary, and other mucosal glands that functions as a natural antibacterial agent. Lactoperoxidase is a member of the heme peroxidase family of enzymes. In humans, lactoperoxidase is encoded by the LPO gene.Lactoperoxidase catalyzes... ), sea urchin Sea urchin Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull... eggs (ovoperoxidase), vanadium bromoperoxidase Vanadium bromoperoxidase Vanadium bromoperoxidase is a haloperoxidase, used to synthesize halogenated organic compounds associated with defense and pigmentation in seaweeds and marine algae. It is the source of the bulk of organobromine compounds in the ocean... ,(marine algae, other marine spp.?), Murex 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 calle "murexes" or "rock snails"... snail bromoperoxidase (does not use I- or Cl-) |
| Iodoperoxidase (IPO) | I– | horseradish Horseradish Horseradish is a perennial plant of the Brassicaceae family, which also includes mustard, wasabi, broccoli, and cabbages. The plant is probably native to south eastern Europe and the Arab World , but is popular around the world today... (horseradish peroxidase Horseradish peroxidase The enzyme horseradish peroxidase , found in horseradish, is used extensively in biochemistry applications primarily for its ability to amplify a weak signal and increase detectability of a target molecule.-Applications:... ) thyroid Thyroid The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage... (thyroid peroxidase Thyroid peroxidase Thyroid peroxidase or thyroperoxidase is an enzyme expressed mainly in the thyroid that liberates iodine for addition onto tyrosine residues on thyroglobulin for the production of thyroxine or triiodothyronine , thyroid hormones. In humans, thyroperoxidase is encoded by the TPO... ) |