Barbiturase
Encyclopedia
Barbiturase is a zinc containing amidohydrolase
. Barbiturase acts as a catalyst
in the second step of oxidative pyrimidine degradation, promoting the ring-opening hydrolysis
of barbituric acid
to ureidomalonic acid. Although grouped into the naturally existing amidohydrolase
s, it demonstrates more homology with cyanuric acid
amidohydrolase. Therefore, it has been proposed that barbiturase, along with cyanuric acid, should be grouped into a new family.
KEGG
(Zn) atom. Absorption spectrum analysis illustrates that zinc is the only cofactor present in barbiturase. Unlike other zinc containing amidohydrolases, the zinc binding motif of barbiturase is found on the carboxylic acid
terminus, specifically at amino acid
s 320 to 324. Several highly conserved histidine
residues were found in the zinc binding motif region of barbiturase, suggesting that histidine residues are involved in zinc binding and are necessary for the catalytic activity of barbiturase. Experiments have shown that barbiturase is sensitive to metal ion chelators
. Finally, barbiturase activity can be blocked upon addition of other metal ions, such as copper and mercury.
The molecular weight of barbiturase is 172000 kD. Its Km is 1.0 mM. Its Vmax is 2.5 µmol/min/mg. The highest enzymatic activity of barbiturase is at pH 8 and 40-45 °C. Above 55 °C barbiturase loses its activity.
, malonate
, and cyanuric acid inhibit the hydrolysis of barbituric acid. Dihydro-L-orotate is an intermediate in the pyrimidine biosynthesis pathway and competitively inhibits barbiturase. In addition, barbituric acid inhibits multiple enzyme
s that are involved in de novo pyrimidine synthesis. These last two points suggest a connection between pyrimidine anabolism and oxidative catabolism.
Barbiturase activity or the existence of oxidative pyrimidine metabolism
has not yet been discovered in mammals.
Amidohydrolase
Amidohydrolases are a type of hydrolase that acts upon amide bonds.They are categorized under EC number EC 3.5.1 and 3.5.2.Examples include:* Beta-lactamase* Histone deacetylase* Urease...
. Barbiturase acts as a catalyst
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
in the second step of oxidative pyrimidine degradation, promoting the ring-opening hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of barbituric acid
Barbituric acid
Barbituric acid or malonylurea or 6-hydroxyuracil is an organic compound based on a pyrimidine heterocyclic skeleton. It is an odorless powder soluble in water. Barbituric acid is the parent compound of barbiturate drugs, although barbituric acid itself is not pharmacologically active...
to ureidomalonic acid. Although grouped into the naturally existing amidohydrolase
Amidohydrolase
Amidohydrolases are a type of hydrolase that acts upon amide bonds.They are categorized under EC number EC 3.5.1 and 3.5.2.Examples include:* Beta-lactamase* Histone deacetylase* Urease...
s, it demonstrates more homology with cyanuric acid
Cyanuric acid
Cyanuric acid or 1,3,5-triazine-2,4,6-triol is a chemical compound with the formula 3. Like many industrially useful chemicals, this triazine has many synonyms. This white, odorless solid finds use as a precursor or a component of bleaches, disinfectants, and herbicides...
amidohydrolase. Therefore, it has been proposed that barbiturase, along with cyanuric acid, should be grouped into a new family.
KEGG
Background
Barbiturase consists of four identical subunits, each bound to a zincZinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
(Zn) atom. Absorption spectrum analysis illustrates that zinc is the only cofactor present in barbiturase. Unlike other zinc containing amidohydrolases, the zinc binding motif of barbiturase is found on the carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
terminus, specifically at amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s 320 to 324. Several highly conserved histidine
Histidine
Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...
residues were found in the zinc binding motif region of barbiturase, suggesting that histidine residues are involved in zinc binding and are necessary for the catalytic activity of barbiturase. Experiments have shown that barbiturase is sensitive to metal ion chelators
Chelation
Chelation is the formation or presence of two or more separate coordinate bonds between apolydentate ligand and a single central atom....
. Finally, barbiturase activity can be blocked upon addition of other metal ions, such as copper and mercury.
The molecular weight of barbiturase is 172000 kD. Its Km is 1.0 mM. Its Vmax is 2.5 µmol/min/mg. The highest enzymatic activity of barbiturase is at pH 8 and 40-45 °C. Above 55 °C barbiturase loses its activity.
Reaction
The equilibrium of the reaction favors the formation of barbituric acid. Barbiturase is very specific to barbituric acid and will not react with derivatives. UreaUrea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
, malonate
Malonate
The malonate or propanedioate ion is CH222− . Malonate compounds include salts and esters of malonic acid, such as*diethyl malonate, 2,*dimethyl malonate, 2,...
, and cyanuric acid inhibit the hydrolysis of barbituric acid. Dihydro-L-orotate is an intermediate in the pyrimidine biosynthesis pathway and competitively inhibits barbiturase. In addition, barbituric acid inhibits multiple enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s that are involved in de novo pyrimidine synthesis. These last two points suggest a connection between pyrimidine anabolism and oxidative catabolism.
Barbiturase activity or the existence of oxidative pyrimidine metabolism
Pyrimidine metabolism
Pyrimidine biosynthesis occurs both in the body and through organic synthesis.-De novo biosynthesis of pyrimidine :Unlike purines, pyrimidines are assembled before being attached to 5-phosphoribosyl-1-pyrophosphate ....
has not yet been discovered in mammals.