Phosphoribosylaminoimidazole carboxylase
Encyclopedia
Phosphoribosylaminoimidazole carboxylase (or AIR carboxylase) is an enzyme
involved in nucleotide
biosynthesis
and in particular in purine biosynthesis. It catalyzes the conversion of 5'-phosphoribosyl-5-aminoimidazole
("AIR") into 5'-phosphoribosyl-4-carboxy-5-aminoimidazole
("CAIR") as described in the reaction:
in plant
s and fungi, but consists of two non-interacting proteins in bacteria, PurK and PurE.
The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme.
Escherichia coli
the reaction is catalyzed in two steps carried out by two separate enzymes, PurK and PurE.
PurK, N5-carboxyaminoimidazole ribonucleotide synthetase, catalyzes the conversion of 5-aminoimidazole ribonucleotide ("AIR"), ATP
, and bicarbonate
to N5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), ADP
, and Pi
.
PurE, N5-carboxyaminoimidazole ribonucleotide mutase, converts N5-CAIR to CAIR, the sixth step of de novo purine biosynthesis. In the presence of high concentrations of bicarbonate, PurE is reported able to convert AIR to CAIR directly and without ATP. Some members of this family contain two copies of this domain.
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...
involved in nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
biosynthesis
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
and in particular in purine biosynthesis. It catalyzes the conversion of 5'-phosphoribosyl-5-aminoimidazole
5'-phosphoribosyl-5-aminoimidazole
5'-Phosphoribosyl-5-aminoimidazole is an intermediate in the formation of purines. Thus, it is an intermediate in the adenine pathway, and is synthesized from 5'-phosphoribosylformylglycinamidine by AIR synthetase....
("AIR") into 5'-phosphoribosyl-4-carboxy-5-aminoimidazole
5'-phosphoribosyl-4-carboxy-5-aminoimidazole
5'-Phosphoribosyl-4-carboxy-5-aminoimidazole is an intermediate in the formation of purines.It is formed by phosphoribosylaminoimidazole carboxylase....
("CAIR") as described in the reaction:
- 5-aminoimidazole ribonucleotide + CO2
5'-phosphoribosyl-4-carboxy-5-aminoimidazole + 2 H+
In plants and fungi
Phosphoribosylaminoimidazole carboxylase is a fusion proteinFusion protein
Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...
in plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s and fungi, but consists of two non-interacting proteins in bacteria, PurK and PurE.
The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme.
In Escherichia coli
In the bacteriumBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
the reaction is catalyzed in two steps carried out by two separate enzymes, PurK and PurE.
PurK, N5-carboxyaminoimidazole ribonucleotide synthetase, catalyzes the conversion of 5-aminoimidazole ribonucleotide ("AIR"), ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, and bicarbonate
Bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
to N5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), ADP
Adenosine diphosphate
Adenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....
, and Pi
Pi
' is a mathematical constant that is the ratio of any circle's circumference to its diameter. is approximately equal to 3.14. Many formulae in mathematics, science, and engineering involve , which makes it one of the most important mathematical constants...
.
PurE, N5-carboxyaminoimidazole ribonucleotide mutase, converts N5-CAIR to CAIR, the sixth step of de novo purine biosynthesis. In the presence of high concentrations of bicarbonate, PurE is reported able to convert AIR to CAIR directly and without ATP. Some members of this family contain two copies of this domain.
