What is a Lyase Definition Classification Mechanism and Examples
In physiology, Lyase meaning is defined as any member of an enzyme class that catalyzes the removal or addition of the elements of ammonia (nitrogen, hydrogen), carbon dioxide (carbon, oxygen), or water (oxygen, hydrogen) at double bonds in different ways other than hydrolysis and oxidation. For example, dehydrases remove water and decarboxylases remove carbon dioxide from amino acids.
Nomenclature
The systematic names can be formed as "substrate group-lyase." Common names are aldolase, dehydratase, decarboxylase, and so on. Synthase may be used in the name of a product when it is very essential, such as phosphosulfolactate synthase sulfite's Michael addition to phosphoenolpyruvate). A combination of both - a Michael and elimination addition is seen in the O-succinylhomoserine (thiol) -lyase (either MetY or MetZ) that catalyze first the γ-elimination of O-succinyl homoserine (succinate as a leaving group) and after that, the sulphide addition to the vinyl intermediate. First, this particular reaction was classified as a lyase, but then, it was reclassified as a transferase.
Examples of Lyase
A few examples of lyase include phenylalanine ammonia-lyase, citrate lyase, isocitrate lyase, hydroxynitrile, pectate lyase, argininosuccinate lyase, pyruvate formate lyase, alginate lyase, and pectin lyase.
Classification
In the classification of enzymes, lyases may be classified further into seven subclasses.
The first group includes Lyases that cleave carbon-carbon bonds and also include decarboxylases, aldehyde lyases by facilitating the aldol condensation's reverse reaction, oxo acid lyases (EC 4.1.3), which catalyzes the cleavage of several 3-hydroxy acids, including others.
The second one has a group of lyases, which break carbon-oxygen bonds like dehydratases. Hydro-lyases, being a part of carbon-oxygen lyases, may facilitate the cleavage of C-O bonds by water elimination. Phosphate reduction or the removal of alcohol from a polysaccharide was promoted by a few other carbon-oxygen lyases.
Lyases cleaving the carbon-nitrogen bonds are. And, they could release ammonia with the powerful cleaving ability and simultaneously produce a double ring or bond. A few of these enzymes may also help to eliminate an amide or amine group.
The fourth group shows lyases that split carbon-sulphur bonds that could either substitute or eliminate hydrogen sulphide (H₂S) from a reaction.
Carbon-halide bonds, by cleaving enzymes, are the lyases in the fifth group and which utilize an action mode, which removes hydrochloric acid from dichloro-diphenyl-trichloroethane (DDT), a synthetic pesticide.
Sixth group comprises the bonds of lyases fracturing phosphorus-oxygen, such as guanylyl cyclase and adenylyl cyclase, and they eliminate phosphate from the nucleotide triphosphates.
Example of Lyases in Each Category
Carbon-Carbon Lyases
Carboxy-Lyases: Pyruvate decarboxylase, acetoacetate decarboxylase, Oxaloacetate decarboxylase, Glutamate decarboxylase, Malonyl-CoA decarboxylase, Ornithine decarboxylase, Phosphoribosylaminoimidazole carboxylase, Lysine decarboxylase, Histidine decarboxylase, Aromatic L-amino acid decarboxylase, Uridine monophosphate synthetase/Orotidine 5'-phosphate decarboxylase, Phosphoenolpyruvate carboxylase, Uroporphyrinogen III decarboxylase, Pyrophosphomevalonate decarboxylase, RUBISCO, Adenosylmethionine decarboxylase, phosphoenolpyruvate carboxykinase
Aldehyde-Lyases: 2-hydroxyphytanoyl-CoA-lyase, aldolase A, aldolase B
Oxo-Acid-Lyases: 3-hydroxy-3-methylglutaryl-CoA lyase
Carbon-Oxygen Lyases: Fumarase, carbonic anhydrase, Enolase (Alpha), aconitase, Enoyl-CoA hydratase/3-Hydroxyacyl ACP dehydrase, Methylglutaconyl-CoA hydratase, Tryptophan synthase, Porphobilinogen synthase, cystathionine beta-synthase, 3-isopropyl malate dehydratase, nitrile hydratase, Urocanate hydratase, Uroporphyrinogen III synthase.
Carbon-Nitrogen Lyases:
Ammonia-Lyases: Histidine ammonia-lyase, Formiminotransferase cyclodeaminase, Serine dehydratase
Amidine-Lyases: Argininosuccinate lyase, Adenylosuccinate lyase
Carbon-Sulphur Lyases: Cystathionine gamma-lyase, Cystathionine-beta-lyase, Leukotriene C4 synthase
Carbon-Halide Lyases: Dichloromethane dehalogenase, Halohydrin dehalogenase
Phosphorus-Oxygen Lyases: guanylate cyclase, adenylate cyclase
Substrate Specificity
Usually, the specificity of a narrow substrate is considered to be a drawback for any enzyme's commercialization because it greatly restricts the enzyme's flexibility as an assistant in the related compound's production. Generally, lyases, but not all the time, are found with narrow substrate specificity. Most of the ammonia and hydratases-lyases possess a quite narrow substrate specificity, whereas the substrate specificity for decarboxylases, oxy nitrilases, and aldolases is much broader.
Note that the substrate specificity of a particular lyase varies based on its source. However, it is not given as an absolute prerequisite for enzymes to own the unrestricted substrate specificity for their commercial exploitation. Also, there are many lyases in commercial use bearing a narrow substrate spectrum.
Co-factor Requirements
The enzyme's commercial potential may be severely limited by the expensive cofactor's requirement. Since the addition catalyzed by lyase does not implicate the mere reduction or oxidation, it is not an important requirement for cofactors. However, till now, many lyases identified do require cofactors that are involved in the stabilization of reaction intermediates, substrate binding, substrate polarisation, temporary binding of the nucleophile, and more.
The majority of these cofactors are covalently bound to the enzyme and are not very expensive. Thereby, the lyases' cofactors do not establish a barrier to their commercialization. The requirements for lyases' cofactors differ as per their different sources.
Lyase Deficiency Disorder
Lyase deficiency, which is also referred to as HMG-CoA lyase deficiency, is given as a rare inherited disorder, which causes a mess in the metabolism of amino acid leucine and also prevents the body from synthesizing ketones, which are used for energy production during the body's food lacking periods. This condition could be inherited in an autosomal recessive pattern, which means that both copies of the gene in every cell undergo mutations.
Usually, the lyase deficiency symptoms express within the life's first year and primarily include vomiting, diarrhea, dehydration, lethargy, and weak muscular development. During the lyase deficiency episode, blood sugar concentrations may be either extremely low or hypoglycemic and a few harmful compounds would be accumulated to cause the blood to become quite acidic.
Whereas, if it is left untreated, the disorder could even initiate convulsions, coma, breathing problems, and also death. Infection, strenuous exercise, and other physical stresses may probably give rise to bouts with the symptoms of lyase deficiency.
FAQs on Lyase Enzymes in Biochemistry
1. What is a lyase in biochemistry?
A lyase is an enzyme that catalyzes the breaking or formation of chemical bonds without using ATP or water, typically forming or removing a double bond. In enzyme classification, lyases are grouped under EC class 4.
- They cleave bonds such as C–C, C–O, C–N, or C–S.
- They often produce a double bond or a ring structure as a result.
- The reverse reaction may involve adding a group across a double bond.
2. What reaction do lyases catalyze?
Lyases catalyze non-hydrolytic bond cleavage or the addition of groups to double bonds. These reactions typically involve elimination or addition mechanisms.
- Elimination reaction: removal of a small molecule to form a double bond.
- Addition reaction: addition of a group to an existing double bond.
- No ATP or water is required for bond breaking.
3. How are lyases different from hydrolases?
The main difference is that lyases break bonds without water, while hydrolases use water to cleave bonds.
- Lyases: non-hydrolytic cleavage, often forming double bonds.
- Hydrolases: hydrolysis reactions involving H2O.
- Lyases belong to EC 4, hydrolases to EC 3.
4. What are the main types of lyases?
Lyases are classified into several types based on the bond they break, all under EC class 4.
- Carbon–carbon lyases (EC 4.1) – e.g., decarboxylases.
- Carbon–oxygen lyases (EC 4.2) – e.g., dehydratases.
- Carbon–nitrogen lyases (EC 4.3).
- Carbon–sulfur lyases (EC 4.4).
5. What is an example of a lyase reaction in glycolysis?
An example of a lyase reaction in glycolysis is the conversion of 2-phosphoglycerate to phosphoenolpyruvate catalyzed by enolase.
- Enzyme: enolase (a carbon–oxygen lyase).
- Reaction type: dehydration (removal of H2O).
- Product formed: phosphoenolpyruvate (contains a double bond).
6. What is a decarboxylase and is it a lyase?
A decarboxylase is a lyase that removes a carboxyl group as CO2 without hydrolysis or oxidation. Decarboxylases belong to EC 4.1 (carbon–carbon lyases).
- They catalyze non-hydrolytic removal of CO2.
- Often require cofactors such as thiamine pyrophosphate (TPP).
- Common in metabolic pathways like the citric acid cycle.
7. Do lyases require ATP to function?
Lyases generally do not require ATP to break chemical bonds.
- Bond cleavage occurs without ATP hydrolysis.
- The reaction is driven by substrate rearrangement or formation of stable products such as double bonds.
- This distinguishes lyases from ligases (EC 6), which require ATP.
8. What is the difference between lyase and ligase?
The key difference is that lyases break or form double bonds without ATP, while ligases join two molecules using ATP.
- Lyases: EC 4, non-hydrolytic cleavage or addition.
- Ligases: EC 6, bond formation coupled to ATP hydrolysis.
- Lyases often create double bonds; ligases form new single bonds.
9. What is the EC number classification for lyases?
Lyases are classified under Enzyme Commission (EC) number 4. The EC system categorizes enzymes based on the reactions they catalyze.
- EC 4.1: Carbon–carbon lyases.
- EC 4.2: Carbon–oxygen lyases.
- EC 4.3: Carbon–nitrogen lyases.
- EC 4.4: Carbon–sulfur lyases.
10. Why are lyases important in metabolism?
Lyases are important in metabolism because they facilitate key bond rearrangements and double-bond formations in pathways like glycolysis and the citric acid cycle.
- They enable decarboxylation and dehydration steps.
- They help generate high-energy intermediates such as phosphoenolpyruvate.
- They contribute to amino acid and carbohydrate metabolism.
