[Chemistry Class Notes] Lyase Pdf for Exam

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.

1. 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.

2. 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.

3. 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.

4. The fourth group shows lyases that split carbon-sulphur bonds that could either substitute or eliminate hydrogen sulphide (H₂S) from a reaction.

5. 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.

6. 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.