Isomerase
[1] They convert one isomer to another, meaning that the end product has the same molecular formula but a different physical structure.
[2] The sub-categories of isomerases containing racemases, epimerases and cis-trans isomers are examples of enzymes catalyzing the interconversion of stereoisomers.
[3] Calculating isomerase kinetics from experimental data can be more difficult than for other enzymes because the use of product inhibition experiments is impractical.
[6] This technique was then adopted to study the profile of proline racemase and its two states: the form which isomerizes L-proline and the other for D-proline.
At high concentrations it was shown that the transition state in this interconversion is rate-limiting and that these enzyme forms may differ just in the protonation at the acidic and basic groups of the active site.
[9] This sub-class can be broken down according to the functional group the enzyme transfers: This category (EC 5.5) includes intramolecular lyases.
The overall reaction involves the opening of the ring to form an aldose via acid/base catalysis and the subsequent formation of a cis-endiol intermediate.
This reaction is a Claisen rearrangement that can proceed with or without the isomerase, though the rate increases 106 fold in the presence of chorismate mutase.
[12] Experimental evidence indicates that the isomerase selectively binds the chair transition state, though the exact mechanism of catalysis is not known.
It is thought that this binding stabilizes the transition state through electrostatic effects, accounting for the dramatic increase in the reaction rate in the presence of the mutase or upon addition of a specifically-placed cation in the active site.
In this isomerization reaction a stable carbon-carbon double bond is rearranged top create a highly electrophilic allylic isomer.
IPP isomerase catalyzes this reaction by the stereoselective antarafacial transposition of a single proton.
PHI is the second most frequent erthoenzyopathy in glycolysis besides pyruvate kinase deficiency, and is associated with non-spherocytic haemolytic anaemia of variable severity.
As in humans, the hemolytic syndrome, which is characterized by a diminished erythrocyte number, lower hematocrit, lower hemoglobin, higher number of reticulocytes and plasma bilirubin concentration, as well as increased liver- and spleen-somatic indices, was exclusively manifested in homozygous mutants.
[16] The disease referred to as triosephosphate isomerase deficiency (TPI), is a severe autosomal recessive inherited multisystem disorder of glycolytic metabolism.
[19] The most common mutation is the substitution of gene, Glu104Asp, which produces the most severe phenotype, and is responsible for approximately 80% of clinical TPI deficiency.
[20] Being an autosomal recessive inherited disease, TPI deficiency has a 25% recurrence risk in the case of heterozygous parents.
These symptoms include: dystonia, tremor, dyskinesia, pyramidal tract signs, cardiomyopathy and spinal motor neuron involvement.
[18] TPI is detected through deficiency of enzymatic activity and the build-up of dihyroxyacetone phosphate(DHAP), which is a toxic substrate, in erythrocytes.
Because of the range of symptoms TPI causes, a team of specialist may be needed to provide treatment to a single individual.
That team of specialists would consists of pediatricians, cardiologists, neurologists, and other healthcare professionals, that can develop a comprehensive plan of action.
[22] Supportive measures such as red cell transfusions in cases of severe anaemia can be taken to treat TPI as well.
High-fructose corn syrup is preferred by many confectionery and soda manufacturers because of the high sweetening power of fructose (twice that of sucrose[25]), its relatively low cost and its inability to crystallize.
[24] Major issues of the use of glucose isomerase involve its inactivation at higher temperatures and the requirement for a high pH (between 7.0 and 9.0) in the reaction environment.
Overall, extensive research in genetic engineering has been invested into optimizing glucose isomerase and facilitating its recovery from industrial applications for re-use.
Glucose isomerase is able to catalyze the isomerization of a range of other sugars, including D-ribose, D-allose and L-arabinose.
The most efficient substrates are those similar to glucose and xylose, having equatorial hydroxyl groups at the third and fourth carbons.
[28] The current model for the mechanism of glucose isomerase is that of a hydride shift based on X-ray crystallography and isotope exchange studies.
