What Is a Peroxidase?
A peroxidase is one of any number of protein-based enzymes that act as catalysts to facilitate a variety of biological processes. Specifically, peroxidase activity involves donating electrons to bind to other substrate substances, such as ferrocyanide and ascorbate, in order to break them down into harmless components. Most notably, peroxidase enzymes degrade hydrogen peroxide, a naturally occurring byproduct of oxygen metabolism in the body. As a result, this substance is converted into water and oxygen.
Investigation into the nature of peroxidases was driven by the discovery of hydrogen peroxide synthesis by the French baron and chemist, Louis Jacques Thénard in the mid-19th century. In contrast to the popular theory of “vitalism” that dominated the scientific community at the time, Thénard proposed that the decomposition of hydrogen peroxide occurred due to the presence of a specific material other than a “vital force.” In short, he initiated the idea that certain enzymes empowered with catalyst properties triggered chemical reactions instead. By the early 1900s, the as yet unknown enzymes at work in the human body were labeled as “catalases,” while the simultaneous observation that plants and animals utilized polyphenols to degrade hydrogen peroxide lead to the term “peroxidases.”
Today, the study of peroxidase function has led to a more comprehensive understanding of the mechanism behind their catalystic activity, which is determined by the availability of electron donation and substrate electron reception. For instance, it is now known that glutathione peroxidase promotes a two-electron conversion to effectively detoxify the body of hydroperoxides without causing free radical damage in the process. However, this substance also uses hydroperoxides as substrates to form bonds with certain proteins involved with redox regulation (oxygen reduction), which is necessary for proper metabolic functioning. In addition, the study of redux modulation afforded by peroxidase agents that contain a heme cofactor, or an iron atom, in their prosthetic groups has spawned new areas of biochemistry, such as enzyme kinetics.
The study of plant-based peroxidases, namely HRP derived from horseradish root, has furthered the fields of molecular biology and immunohistochemistry, also known as histochemistry. In the former, HRP is used to detect peroxidase antibodies that may indicate a metabolic disorder, such as thyroid disease. It is also used to measure serum or urine levels of glucose. As a diagnostic tool in pathology, HRP has the ability to target and bind to certain biomarkers found in cancerous cells and produce a stain reaction when introduced to biopsy samples. Aside from being readily available and inexpensive to obtain, HRP is considered particularly useful for such tests due to being highly stable and open to reacting with a variety of substrates.
Written by Karyn Maier
