Enzymes are biological macromolecules that catalyze chemical reactions, accelerating the rate of metabolic processes essential to life. These proteins lower the activation energy of reactions, making biochemical transformations more efficient and sustainable. Enzymes are essential for cellular functions ranging from digestion and energy production to DNA replication and signal transduction.

Enzymes are classified based on the types of reactions they catalyze, and the International Union of Biochemistry and Molecular Biology (IUBMB) has categorized them into six major classes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Creative Enzymes offers a wide range of high-quality enzymes under all enzyme categories to meet your research and industrial needs.

Oxidoreductases: Catalysts of Redox Reactions

Definition and Role

Oxidoreductases are a class of enzymes that facilitate oxidation-reduction (redox) reactions involving the transfer of electrons from one molecule (electron donor) to another (electron acceptor). These reactions are critical for maintaining cellular energy balance, biosynthesis, and detoxification.

Oxidoreductases are particularly important in:

• Cellular respiration, where they help generate ATP by transferring electrons through the electron transport chain.
• Photosynthesis, where they participate in the conversion of solar energy into chemical energy.
• Detoxification, where they break down harmful reactive oxygen species (ROS) such as hydrogen peroxide.
• Biosynthesis, where they contribute to the formation of essential biomolecules such as fatty acids and nucleotides.

Most oxidoreductases require coenzymes such as NAD⁺, NADP⁺, FAD, and FMN, which act as electron carriers to facilitate redox reactions.

Key Examples and Their Functions

• Dehydrogenases: Dehydrogenases catalyze the removal of hydrogen atoms from substrates, typically transferring them to electron carriers such as NAD⁺ or FAD. They are essential for cellular respiration and metabolic pathways.
• Oxidases: Oxidases catalyze the transfer of electrons to molecular oxygen, often producing water or hydrogen peroxide as a by-product. Cytochrome oxidase is a specific example, a critical enzyme in the electron transport chain (ETC) located in the mitochondrial membrane. Cytochrome oxidase transfers electrons from cytochrome c to oxygen, which drives ATP synthesis through oxidative phosphorylation. Defects in cytochrome oxidase can lead to severe mitochondrial diseases.
• Peroxidases: Peroxidases break down hydrogen peroxide (H₂O₂), preventing oxidative damage to cells. Catalase is a peroxidase that breaks down H₂O₂ into water and oxygen, neutralizing toxic byproducts of metabolism. Catalase is found in almost all aerobic organisms, especially in liver and kidney cells. Catalase deficiency can lead to acatalasia, a rare disorder associated with tissue damage due to oxidative stress.
• Reductases: Reductases facilitate reduction reactions, often working in conjunction with oxidases and dehydrogenases. One example is ribonucleotide reductase (RNR), which converts ribonucleotides to deoxyribonucleotides, essential for DNA synthesis and replication. RNR is a target for cancer therapy because of its critical role in cell proliferation.

Figure 1. Examples for an oxidation reaction with malate dehydrogenase (top) and for a reduction with homoserine dehydrogenase (bottom). The transformation of a hydroxyl group into a ketone function or vice versa (red) is carried out in both reactions. (Klebe, 2013)

Biological Importance

Oxidoreductases are essential for maintaining redox balance and ensuring the proper functioning of metabolic pathways. Their biological importance includes energy metabolism, where enzymes such as dehydrogenases and oxidases drive cellular respiration and produce ATP, while dysfunction can lead to mitochondrial diseases and metabolic disorders. They also play a critical role in detoxifying reactive oxygen species (ROS), as peroxidases and catalases protect cells from oxidative stress, and ROS accumulation is associated with neurodegenerative diseases such as Parkinson's and Alzheimer's, as well as with aging. In addition, oxidoreductases are essential for biosynthetic processes, where reductases help synthesize essential biomolecules such as nucleotides, fatty acids, and steroids, and impaired oxidoreductase function can lead to developmental abnormalities and metabolic syndromes.

Transferases: Facilitators of Molecular Transfer

Definition and Role

Transferases are enzymes that catalyze the transfer of functional groups (e.g., phosphate, methyl, amino) from one molecule to another. These enzymes are crucial in various biochemical processes, including:

• Metabolism, where they facilitate the transformation of biomolecules.
• Signal transduction, by regulating the phosphorylation and dephosphorylation of proteins.
• Gene expression, through epigenetic modifications like methylation.

Transferases enable cells to adapt to environmental changes and maintain homeostasis.

Key Examples and Their Functions

• Kinases: Kinases transfer phosphate groups (PO₄^3-) from ATP to proteins, lipids, or other molecules to regulate signaling pathways. An important classification of kinases is protein kinases, which control cell division, differentiation, and apoptosis. Tyrosine kinases regulate growth factor signaling (e.g. EGFR in cancer progression).
• Transaminases (Aminotransferases): Transaminases facilitate the transfer of amino groups between amino acids and keto acids, which is essential for amino acid metabolism. A specific example is alanine aminotransferase (ALT), which converts alanine and α-ketoglutarate to pyruvate and glutamate.
• Methyltransferases: Methyltransferases add methyl groups (-CH₃) to DNA, RNA, proteins, or small molecules, thereby affecting gene regulation. DNA methyltransferase (DNMT) catalyzes the methylation of cytosine residues in DNA, thereby regulating gene expression.

Figure 2. General scheme of kinase function.

Biological Importance

Kinases are critical regulators of cellular function, metabolism, and genetic control, playing essential roles in diverse biological processes. In cell signaling and communication, kinases modulate signal transduction pathways that control growth, apoptosis, and immune responses, while abnormal kinase activity is associated with cancer, neurodegeneration, and metabolic disorders. In metabolism and energy production, transaminases are essential for amino acid biosynthesis and nitrogen balance, and their deficiencies can lead to neurological disorders and metabolic diseases. In epigenetic regulation and gene expression, methyltransferases influence chromatin remodeling and transcriptional silencing, with epigenetic changes contributing to cancer, neurodevelopmental disorders, and aging. In addition, in disease, overactive kinases are targets for cancer therapies such as tyrosine kinase inhibitors, and DNA methylation patterns serve as biomarkers for disease diagnosis and prognosis.

Hydrolases: The Bond Breakers

Definition and Role

Hydrolases are enzymes that catalyze the hydrolysis of chemical bonds by incorporating water molecules. This reaction results in the breakdown of complex biomolecules into simpler components, making hydrolases essential for digestion, intracellular recycling, and metabolic regulation. These enzymes function in a variety of biological systems, facilitating nutrient absorption, cellular maintenance, and waste management. They play a central role in homeostasis by ensuring that macromolecules are efficiently broken down and their components reused or excreted.

Key Examples and Their Functions

• Proteases (Peptidases): Enzymes that hydrolyze peptide bonds in proteins, breaking them down into smaller peptides or free amino acids. Examples include trypsin and pepsin, which play important roles in digestive processes.
• Lipases: Enzymes that catalyze the breakdown of lipids into glycerol and fatty acids. For example, pancreatic lipase is essential for the digestion of dietary fats in the small intestine.
• Amylases: Enzymes responsible for hydrolyzing starch and glycogen into simpler sugars like maltose and glucose. Salivary amylase initiates carbohydrate digestion in the mouth.
• Nucleases: Enzymes that cleave the phosphodiester bonds in nucleic acids, breaking down DNA and RNA into their nucleotide components. Examples include DNAse and RNAse, which are vital for nucleic acid metabolism and turnover.

Figure 3. General enzymatic reaction of a lipase. Under natural conditions lipases catalyze the hydrolysis of triacylglycerol into a diglyceride and fatty acid. In non-aqueous environment, lipases can also catalyze ester synthesis (Reproduced from Jaeger et al., 1994).

Biological Importance

Hydrolases are essential for maintaining biological function. Their role in breaking down food molecules enables nutrient absorption, while their involvement in cellular turnover helps eliminate damaged or old biomolecules. Inadequate hydrolase activity can lead to serious diseases such as lysosomal storage disorders, in which dysfunctional enzyme activity leads to the accumulation of macromolecules in cells, causing progressive tissue and organ damage. Similarly, deficiencies in digestive hydrolases contribute to gastrointestinal disorders and malnutrition.

Lyases: The Bond Cleavers

Definition and Role

Lyases are enzymes that catalyze the cleavage of various chemical bonds without the involvement of water or oxidation-reduction reactions. These enzymes often facilitate the formation of double bonds or cyclic structures, making them essential for metabolic pathways and biosynthetic processes. Lyases enable the removal of functional groups, creating molecules that serve as intermediates in essential biochemical reactions.

Key Examples and Their Functions

• Decarboxylases: Remove carboxyl (-COO-) groups from organic molecules, producing carbon dioxide as a byproduct. Pyruvate decarboxylase is a key enzyme in fermentation, converting pyruvate to acetaldehyde and CO₂.
• Aldolases: Break carbon-carbon bonds and play an important role in metabolic pathways such as glycolysis. Aldolase A is involved in the splitting of fructose 1,6-bisphosphate into two three-carbon molecules for energy production.
• Synthases: Facilitate the formation of new bonds without ATP hydrolysis. For example, citrate synthase is a key enzyme in the Krebs cycle that links acetyl-CoA and oxaloacetate to form citrate, an essential intermediate in energy metabolism.

Figure 4. All aldolase family members regulate glycolysis. They catalyze the conversion of fructose 1,6-bisphosphatase to glyceraldehyde 3-phosphate (glyceraldehyde 3P) and dihydroxyacetone phosphate (DHAP). ALDOA plays a major role depending on its activity and low K_m. ALDOB and ALDOC are also involved in the fructolysis process for glyceraldehyde production. TCA, tricarboxylic acid. (Chang et al., 2018)

Biological Importance

Lyases are integral to energy production, biosynthetic pathways, and the regulation of metabolic flux. They contribute to the synthesis of essential biomolecules such as amino acids, hormones, and nucleotides. Dysfunctional lyase activity can lead to metabolic imbalances that affect energy homeostasis and biosynthesis, potentially resulting in conditions such as lactic acidosis and certain genetic disorders associated with impaired enzyme function.

Isomerases: Molecular Rearrangers

Definition and Role

Isomerases are enzymes that catalyze the rearrangement of molecular structures without adding or removing atoms. This conversion between isomers is critical for metabolic processes, ensuring the proper configuration of biomolecules required for efficient biochemical function. These enzymes are particularly important in sugar metabolism, nucleotide synthesis and hormone regulation.

Key Examples and Their Functions

• Racemases: Convert molecules into their mirror-image enantiomers, ensuring the correct configuration of biological compounds. For example, alanine racemase plays a key role in bacterial cell wall synthesis by converting L-alanine to D-alanine.
• Epimerases: Change the stereochemistry of a single chiral carbon within a molecule. UDP-glucose epimerase converts UDP-glucose to UDP-galactose, a critical step in carbohydrate metabolism.
• Mutases: Transfer functional groups within the same molecule, enabling critical metabolic transitions. For example, phosphoglucomutase interconverts glucose-1-phosphate and glucose-6-phosphate in glycogen metabolism.

Figure 5. Reversible conversion of glucose to fructose catalyzed by glucose isomerase. (Paul et al., 2019)

Biological Importance

Isomerases provide metabolic flexibility and contribute to the precise regulation of biomolecules. They ensure that biochemical reactions proceed efficiently by adapting molecular configurations to specific enzymatic requirements. Deficiencies in isomerases can lead to metabolic disorders, including inborn errors of carbohydrate metabolism such as galactosemia, where improper conversion of galactose leads to toxic accumulation.

Ligases: The Bond Builders

Definition and Role

Ligases are enzymes that catalyze the joining of two molecules, often requiring ATP hydrolysis to drive the reaction. These enzymes are fundamental to genetic processes, biosynthesis, and energy metabolism. Ligases play an essential role in joining DNA fragments, forming peptide bonds, and incorporating carbon groups into metabolic intermediates.

Key Examples and Their Functions

• DNA Ligases: Repair DNA by sealing breaks in the sugar-phosphate backbone during replication and recombination. DNA ligase I is essential for maintaining genome integrity.
• Synthetases: Catalyze the formation of complex molecules using ATP energy. For example, glutamine synthetase incorporates ammonia into glutamate to form glutamine, which is essential for nitrogen metabolism.
• Carboxylases: Add carboxyl groups (-COO-) to molecules to facilitate biosynthetic pathways. Pyruvate carboxylase is essential for gluconeogenesis, converting pyruvate to oxaloacetate to produce glucose.

Figure 6. Ligases catalyze reactions that involve the creation of chemical bonds with nucleotide triphosphates. (Paul et al., 2019)

Biological Importance

Ligases are essential for genetic stability, the synthesis of essential biomolecules, and the regulation of metabolic pathways. Their activity ensures the proper replication and repair of genetic material, the formation of structural proteins, and the efficient utilization of metabolic substrates. Ligase dysfunction is associated with genetic disorders, such as DNA repair defects, and metabolic conditions, where improper bond formation leads to dysregulated biochemical homeostasis.

Figure 7. A summary of the six types of enzymes. Non-enzymatic counterparts of six enzymes representatives to the six general chemical reaction types/main classes of enzymatic reactions (top hierarchical level of enzyme commission number). Enzymes are exemplified by crystallographic structures illustrated in pymol; Protein Structure Databank (PDB, accession codes: 8CAT (catalase), 1PKW (human glutathione transferase A1-1), 2J0E (6-phosphogluconolactonase), 1N8P (PLP-dependent cystathionine gamma-lyase), 4OWG (triosephosphate isomerase) and 2G36 (iron–sulfur cluster containing tryptophanyl-tRNA synthetase). (Keller et al., 2015)

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