**Glycine N-benzoyltransferase**
**Definition**
Glycine N-benzoyltransferase is an enzyme that catalyzes the transfer of a benzoyl group from benzoyl-CoA to glycine, producing N-benzoylglycine (hippuric acid) and Coenzyme A. It plays a key role in the detoxification and metabolism of aromatic compounds in various organisms.
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## Glycine N-benzoyltransferase
### Overview
Glycine N-benzoyltransferase (EC 2.3.1.71) is a member of the acyltransferase family of enzymes, specifically those transferring acyl groups other than aminoacyl groups. It facilitates the conjugation of benzoyl-CoA with glycine to form N-benzoylglycine, commonly known as hippuric acid. This enzymatic reaction is an important biochemical pathway in the metabolism and detoxification of aromatic compounds, particularly benzoate derivatives, in animals and some microorganisms.
### Nomenclature and Classification
The enzyme is systematically named benzoyl-CoA:glycine N-benzoyltransferase. It is also referred to as benzoyl-CoA:glycine N-acyltransferase or simply benzoyl-CoA:glycine acyltransferase. The enzyme is classified under the Enzyme Commission number EC 2.3.1.71, indicating its function as an acyltransferase transferring acyl groups to nitrogen atoms.
### Biochemical Reaction
The primary reaction catalyzed by glycine N-benzoyltransferase is:
**Benzoyl-CoA + Glycine → Coenzyme A + N-benzoylglycine (hippuric acid)**
In this reaction, the benzoyl group from benzoyl-CoA is transferred to the amino group of glycine, forming hippuric acid. This conjugation reaction increases the solubility of benzoate derivatives, facilitating their excretion from the body.
### Biological Role and Significance
Glycine N-benzoyltransferase plays a crucial role in the detoxification of benzoic acid and related aromatic compounds. Benzoic acid is a common preservative and environmental contaminant, and its metabolism is essential for preventing toxicity. The enzyme-mediated conjugation with glycine produces hippuric acid, which is water-soluble and readily excreted in urine.
This detoxification pathway is particularly significant in the liver and kidney tissues of mammals, where glycine N-benzoyltransferase is predominantly expressed. The enzyme contributes to the metabolism of dietary and xenobiotic aromatic compounds, aiding in their clearance from the body.
### Distribution in Organisms
Glycine N-benzoyltransferase is found primarily in vertebrates, including humans, rodents, and other mammals. It is localized mainly in the mitochondrial matrix of liver and kidney cells. Some microorganisms also possess similar enzymatic activities, although the specific enzymes and pathways may vary.
### Molecular Structure and Properties
The enzyme is a mitochondrial protein with a molecular weight typically ranging between 30 to 40 kDa, depending on the species. It belongs to the family of CoA-dependent acyltransferases and contains conserved motifs responsible for binding benzoyl-CoA and glycine substrates.
Structural studies, including crystallography and homology modeling, have revealed that glycine N-benzoyltransferase has a characteristic fold common to acyltransferases, with distinct binding pockets for the acyl donor (benzoyl-CoA) and the acceptor (glycine). The active site facilitates nucleophilic attack by the amino group of glycine on the thioester bond of benzoyl-CoA, enabling the transfer of the benzoyl group.
### Mechanism of Action
The catalytic mechanism involves the formation of a tetrahedral intermediate during the transfer of the benzoyl group. Initially, benzoyl-CoA binds to the enzyme, positioning the thioester bond adjacent to the active site residues. Glycine then binds, and its amino group attacks the carbonyl carbon of the benzoyl moiety, forming the intermediate. Subsequent collapse of this intermediate releases Coenzyme A and forms N-benzoylglycine.
Key amino acid residues in the active site stabilize the transition state and facilitate proton transfers necessary for catalysis. The enzyme operates under physiological conditions, with optimal activity at neutral to slightly alkaline pH.
### Regulation and Expression
The expression of glycine N-benzoyltransferase is regulated at the transcriptional and post-translational levels, often influenced by the availability of substrates and the presence of xenobiotics. Induction of the enzyme can occur in response to increased exposure to benzoate compounds, enhancing the organism’s capacity to detoxify these substances.
Hormonal regulation and nutritional status may also affect enzyme levels, reflecting the metabolic demands and detoxification needs of the organism.
### Clinical and Environmental Relevance
The activity of glycine N-benzoyltransferase has clinical significance in the context of exposure to benzoic acid and related compounds. Elevated levels of hippuric acid in urine are often used as biomarkers for exposure to toluene and other aromatic solvents in occupational and environmental health assessments.
Deficiencies or alterations in the enzyme’s activity can impact the metabolism of benzoate derivatives, potentially leading to accumulation of toxic intermediates. However, such deficiencies are rare and not well characterized in human disease.
In environmental microbiology, understanding glycine N-benzoyltransferase and related enzymes contributes to bioremediation strategies aimed at degrading aromatic pollutants.
### Research and Applications
Research on glycine N-benzoyltransferase includes studies on its structure-function relationships, substrate specificity, and role in xenobiotic metabolism. The enzyme serves as a model for studying acyltransferase mechanisms and mitochondrial detoxification pathways.
Biotechnological applications may involve engineering the enzyme or its pathway for enhanced degradation of environmental pollutants or for biosynthesis of conjugated compounds with pharmaceutical relevance.
### Related Enzymes and Pathways
Glycine N-benzoyltransferase is part of a broader family of acyltransferases involved in amino acid conjugation reactions. Similar enzymes catalyze the conjugation of other acyl-CoA derivatives with amino acids, such as glycine N-acyltransferase, which acts on a variety of acyl-CoA substrates.
The enzyme functions within the benzoate metabolism pathway, which includes benzoate activation to benzoyl-CoA by benzoyl-CoA synthetase and subsequent conjugation by glycine N-benzoyltransferase.
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**Meta Description:**
Glycine N-benzoyltransferase is an enzyme that catalyzes the conjugation of benzoyl-CoA with glycine to form hippuric acid, playing a vital role in the detoxification of aromatic compounds in mammals. It is primarily expressed in liver and kidney mitochondria and is important for metabolic clearance of benzoate derivatives.