biochemistry Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, a ...

, ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) is a chemical compound used to observe the

reaction kinetics Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is different from chemical thermodynamics, which deals with the direction in which a ...

of specific

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s. A common use for it is in the enzyme-linked immunosorbent assay (ELISA) to detect the binding of molecules to each other. It is commonly used as a substrate with

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 viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

for a

peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides, and should not be confused with other ...

enzyme (such as

horseradish peroxidase The enzyme horseradish peroxidase (HRP), found in the roots of horseradish, is used extensively in biochemistry applications. It is a metalloenzyme with many isoforms, of which the most studied type is C. It catalyzes the oxidation of various or ...

) or alone with blue multicopper oxidase enzymes (such as laccase or bilirubin oxidase). Its use allows the reaction kinetics of peroxidases themselves to be followed. In this way it also can be used to indirectly follow the reaction kinetics of any

-producing enzyme, or to simply quantify the amount of hydrogen peroxide in a sample. The formal reduction potentials for ABTS are high enough for it to act as an electron donor for the reduction of oxo species such as molecular oxygen and hydrogen peroxide, particularly at the less-extreme pH values encountered in biological catalysis. Under these conditions, the sulfonate groups are fully deprotonated and the mediator exists as a dianion. :ABTS^–· + e^– → ABTS^2– E° = 0.67 V vs SHE :ABTS + e^– → ABTS^–· E° = 1.08 V vs SHE This compound is chosen because the enzyme facilitates the reaction with hydrogen peroxide, turning it into a green and

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

end-product. Its new

absorbance Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". Alternatively, for samples which scatter light, absorbance may be defined as "the negative log ...

maximum of 420 nm

light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...

(ε = 3.6 × 10⁴ M^–1 cm^–1) can easily be followed with a spectrophotometer, a common laboratory instrument. It is sometimes used as part of a

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

estimating

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

when finding glucose concentrations of solutions such as

blood serum Serum () is the fluid and solvent component of blood which does not play a role in clotting. It may be defined as blood plasma without the clotting factors, or as blood with all cells and clotting factors removed. Serum contains all proteins ex ...

. ABTS is also frequently used by the food industry and agricultural researchers to measure the

antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...

capacities of foods. In this assay, ABTS is converted to its radical cation by addition of

sodium persulfate Sodium persulfate is the inorganic compound with the formula Na2 S2 O8. It is the sodium salt of peroxydisulfuric acid, H2S2O8, an oxidizing agent. It is a white solid that dissolves in water. It is almost non-hygroscopic and has good shelf-life. ...

. This radical cation is blue in color and absorbs light at 415, 645, 734 and 815 nm. The ABTS radical cation is reactive towards most antioxidants including phenolics,

thiols In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

and

Vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits, berries and vegetables. It is also a generic prescription medication and in some countries is sold as a non-prescription di ...

. During this reaction, the blue ABTS radical cation is converted back to its colorless neutral form. The reaction may be monitored spectrophotometrically. This assay is often referred to as the Trolox equivalent antioxidant capacity (TEAC) assay. The reactivity of the various antioxidants tested are compared to that of Trolox, which is a water-soluble analog of

vitamin E Vitamin E is a group of eight compounds related in molecular structure that includes four tocopherols and four tocotrienols. The tocopherols function as fat-soluble antioxidants which may help protect cell membranes from reactive oxygen speci ...

Applications for functional food analysis

Based on the special chemical properties of formed free radicals, ABTS assay has been used to determine the antioxidant capacity of food products. For example, polyphenol compounds, which widely exist in fruit, can quench free radicals inside human body, thus prevent oxidative damage by free radicals. The antioxidant potency of plant extract or food product has been measured by ABTS assay. One example with detailed method is the antioxidant activity analysis of Hibiscus products.

References

{{DEFAULTSORT:Abts Biochemistry methods Enzyme kinetics Sulfonic acids Benzothiazolines