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A classic example of ring opening and contraction is the isomerization of glucose (an aldehyde with a six-membered ring) to fructose (a ketone with a five-membered ring). The conversion of D-glucose-6-phosphate to D-fructose-6-phosphate is catalyzed by glucose-6-phosphate isomerase , an intramolecular oxidoreductase .
In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. [1] Enolization is an example of isomerization, as is tautomerization .
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form a ...
Then, the substrate is rotated about the C3-C4 bond to position it for isomerization. At this point, Glu357 deprotonates C2 to create a cis-enediolate intermediate stabilized by Arg272. To complete the isomerization, Glu357 donates its proton to C1, the C2 hydroxyl group loses its proton and the open-chain ketose fructose 6-phosphate is formed.
Skeletal isomerization is not normally encountered in the laboratory, but is the basis of large applications in oil refineries. In general, straight-chain alkanes are converted to branched isomers by heating in the presence of a catalyst. Examples include isomerisation of n-butane to isobutane and pentane to isopentane. Highly branched alkanes ...
A photoswitch is a type of molecule that can change its structural geometry and chemical properties upon irradiation with electromagnetic radiation.Although often used interchangeably with the term molecular machine, a switch does not perform work upon a change in its shape whereas a machine does. [1]
Isomerization of azobenzene, induced by light (hν) or heat (Δ) The most important elementary reactions are unimolecular and bimolecular reactions. Only one molecule is involved in a unimolecular reaction; it is transformed by isomerization or a dissociation into one or more other molecules. Such reactions require the addition of energy in the ...
If it does bind the furanose ring, it next opens the ring. Then the enzyme forms the eneldiol which is stabilized by a lysine or arginine residue. [ 6 ] [ 8 ] Calculations have demonstrated that this stabilization is the most significant contributor to the overall catalytic activity of this isomerase and a number of others like it.