In enzymology, a ribulose-phosphate 3-epimerase (also known as pentose-5-phosphate 3-epimerase or PPE) is the enzyme that converts D-ribulose 5-phosphate into D-xylulose 5-phosphate in Calvin's reductive pentose phosphate cycle

Calvin cycle

The Calvin cycle or Calvin–Benson-Bassham cycle or reductive pentose phosphate cycle or C3 cycle or CBB cycle is a series of biochemical redox reactions that take place in the stroma of chloroplasts in photosynthetic organisms...

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D-ribulose 5-phosphate D-xylulose 5-phosphate

Hence, this enzyme has one substrate

Substrate (biochemistry)

In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...

, D-ribulose 5-phosphate, and one product

Product (chemistry)

Product are formed during chemical reactions as reagents are consumed. Products have lower energy than the reagents and are produced during the reaction according to the second law of thermodynamics. The released energy comes from changes in chemical bonds between atoms in reagent molecules and...

, D-xylulose 5-phosphate.

This enzyme belongs to the family of isomerase

Isomerase

In biochemistry, an isomerase is an enzyme that catalyzes the structural rearrangement of isomers. Isomerases thus catalyze reactions of the formwhere B is an isomer of A.-Nomenclature:...

s, specifically those racemases and epimerases acting on carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

s and derivatives.

In Alcaligenes eutrophus

Alcaligenes eutrophus

Alcaligenes eutrophus is a bacterial species that naturally produces polyhydroxyalkanoates . PHAs are a broad type of biodegradable polymers that can be used for biodegradable plastics. A...

two copies of the gene coding for PPE are known, one is chromosomally encoded , the other one is on a plasmid . PPE has been found in a wide range of bacteria, archaebacteria, fungi and plants. All the proteins have from 209 to 241 amino acid residues. The enzyme has a TIM barrel

TIM barrel

The TIM barrel is a conserved protein fold consisting of eight α-helices and eight parallel β-strands that alternate along the peptide backbone. The structure is named after triosephosphate isomerase, a conserved glycolytic enzyme. TIM barrels are quite common among the conserved protein folds...

 structure.

The systematic name of this enzyme class is D-ribulose-5-phosphate 3-epimerase. Other names in common use include phosphoribulose epimerase, erythrose-4-phosphate isomerase, phosphoketopentose 3-epimerase, xylulose phosphate 3-epimerase, phosphoketopentose epimerase, ribulose 5-phosphate 3-epimerase, D-ribulose phosphate-3-epimerase, D-ribulose 5-phosphate epimerase, D-ribulose-5-P 3-epimerase, D-xylulose-5-phosphate 3-epimerase, and pentose-5-phosphate 3-epimerase.

This enzyme participates in 3 metabolic pathways

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

: pentose phosphate pathway

Pentose phosphate pathway

The pentose phosphate pathway is a process that generates NADPH and pentoses . There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars...

, pentose and glucuronate interconversions, and carbon fixation

Carbon fixation

In biology, carbon fixation is the reduction of carbon dioxide to organic compounds by living organisms. The obvious example is photosynthesis. Carbon fixation requires both a source of energy such as sunlight, and an electron donor such as water. All life depends on fixed carbon. Organisms that...

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Structural studies

As of late 2007, 4 structures

Tertiary structure

In biochemistry and molecular biology, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...

 have been solved for this class of enzymes, with PDB

Protein Data Bank

The Protein Data Bank is a repository for the 3-D structural data of large biological molecules, such as proteins and nucleic acids....

accession codes , , , and .