The catalase is an oxidoreductase enzyme (H2O2: H2O2 oxidoreductase) widely distributed in nature. It catalyzes, in various tissues and cell types, the "breakdown" reaction of hydrogen peroxide into molecular oxygen and water.
The first observations of this type of enzyme date back to the early 1810s, but it was in 1901 that Loew recognized that catalase is present in virtually all existing living organisms and in multiple different cell types.
Molecular structure of the enzyme Catalase (Source: Vossman via Wikimedia Commons)
This enzyme, crucial for the maintenance of cellular integrity and the main regulator of hydrogen peroxide metabolism, was a fundamental factor to be able to affirm that in nature there are enzymes that act on specific substrates.
Mammals and other organisms possess catalase enzymes that can also behave as peroxidases, catalyzing redox reactions of different substrates using hydrogen peroxide.
In most eukaryotes, catalase enzymes are predominantly found in subcellular organelles known as "peroxisomes", and in humans there are numerous pathological conditions related to the deficiency of this enzyme.
characteristics
The activity of enzymes like catalase can vary considerably depending on the type of tissue considered. In mammals, for example, catalase activity is significant in both the kidneys and the liver, and is much lower in connective tissues.
Thus, catalase in mammals is primarily associated with all tissues exhibiting significant aerobic metabolism.
Mammals possess catalases in both mitochondria and peroxisomes, and in both compartments they are enzymes associated with organellar membranes. In erythrocytes, in contrast, catalase activity is associated with a soluble enzyme (remember that erythrocytes have few internal organelles).
Catalase is an enzyme with a high turnover number or catalytic constant (it is very fast and efficient) and the general reaction that it catalyzes is the following:
2H2O2 → 2H2O + O2
In the presence of low concentrations of hydrogen peroxide, mammalian catalase, for example, behaves like an oxidase, using instead molecular oxygen (O2) to oxidize molecules such as indole and β-phenylethylamine, precursors of the amino acid tryptophan and a neurotransmitter, respectively.
Some competitive inhibitors of catalase activity are currently known, notably sodium azide and 3-aminotriazole. Azide, in its anionic form, is a powerful inhibitor of other proteins with heme groups and is used to eliminate or prevent the growth of microorganisms under different conditions.
Structure
In humans, catalase is encoded by a 34 kb gene that has 12 introns and 13 exons and encodes a 526 amino acid protein.
Most of the catalases studied are tetrameric enzymes with a molecular weight close to 240 kDa (60 kDa for each subunit) and each monomer is associated with a prosthetic hemin or ferroprotoporphyrin group.
Its structure is made up of four domains composed of secondary structures formed by alpha helices and beta-folded sheets, and studies carried out in the liver enzyme of humans and bovines have shown that these proteins are bound to four NADPH molecules.
These NADPH molecules do not appear to be essential for the enzymatic activity of catalase (for the production of water and oxygen from hydrogen peroxide), but they do seem to be related to a decrease in the susceptibility of this enzyme to high concentrations of its toxic substrate.
The domains of each subunit in human catalase are:
-A non-globular extended N-terminal arm, which functions for the stabilization of the quaternary structure
-A β-barrel of eight antiparallel β-folded sheets, which contribute some of the lateral binding residues to the heme group
-A "envelope" domain that surrounds the outer domain, including the heme group and, finally
-A domain with alpha helix structure
The four subunits, with these four domains, are responsible for the formation of a long channel whose size is critical for the mechanism of recognition of hydrogen peroxide by the enzyme (which uses amino acids such as histidine, asparagine, glutamine and aspartic acid to it).
Features
According to some authors, catalase fulfills two enzymatic functions:
-The decomposition of hydrogen peroxide into water and molecular oxygen (as a specific peroxidase).
-Oxidation of proton donors, such as methanol, ethanol, many phenols and formic acid, using one mole of hydrogen peroxide (as a non-specific peroxidase).
-In erythrocytes, the large amount of catalase seems to play an important role in the protection of hemoglobin against oxidizing agents, such as hydrogen peroxide, ascorbic acid, methylhydrazine and others.
The enzyme present in these cells is responsible for the defense of other tissues with little catalase activity against high concentrations of hydrogen peroxide.
-Some insects such as the bombardier beetle use catalase as a defense mechanism, as they decompose hydrogen peroxide and use the gaseous oxygen product of this reaction to propel the release of water and other chemical compounds in the form of vapor.
-In plants, catalase (also present in peroxisomes) is one of the components of the photorespiration mechanism, during which the phosphoglycollate produced by the enzyme RuBisCO is used for the production of 3-phosphoglycerate.
Related pathologies in humans
The main sources of production of the substrate for catalase, hydrogen peroxide, are reactions catalyzed by oxidase enzymes, reactive oxygen species and some tumor cells.
This compound is involved in inflammatory processes, in the expression of adhesive molecules, in apoptosis, in the regulation of platelet aggregation and in the control of cell proliferation.
When there are deficiencies of this enzyme, high concentrations of its substrate are generated, which causes lesions in the cell membrane, defects in electron transport in mitochondria, in homocysteine metabolism and in DNA.
Among the diseases associated with mutations in the coding gene for human catalase are:
-Mellitus diabetes
-Arterial hypertension
-Alzheimer
-Vitiligo and others
References
- Agar, N., Sadrzadeh, S., Hallaway, P., & Eaton, J. (1986). Erythrocyte Catalase. A Somatic Oxidant Defense? J. Clin. Invest., 77, 319–321.
- Góth, L., Rass, P., & Páy, A. (2004). Catalase Enzyme Mutations and their Association with Diseases. Molecular Diagnosis, 8 (3), 141–149.
- Kirkman, H., & Gaetanit, GF (1984). Catalase: A tetrameric enzyme with four tightly bound molecules of NADPH. Proc. Natl. Acad. Sci. USA, 81, 4343-4347.
- Kirkman, HN, & Gaetani, GF (2006). Mammalian catalase: a venerable enzyme with new mysteries. Trends in Biochemical Sciences, 32 (1), 44–50.
- Rawn, JD (1998). Biochemistry. Burlington, Massachusetts: Neil Patterson Publishers.
- Solomon, E., Berg, L., & Martin, D. (1999). Biology (5th ed.). Philadelphia, Pennsylvania: Saunders College Publishing.
- Vainshtein, B., Melik-Adamyan, W., Barynin, V., Vagin, A., & Grebenko, A. (1981). Three-dimensional structure of the enzyme catalase. Nature, 293 (1), 411-412.