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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 .
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.
Example mechanism for alkyne zipper reaction. The 3-aminopropylamine anion attacks the same lesser-substituted carbon adjacent to the allene , removing a proton and catalyzing a similar process, where the electrons from the carbon-hydrogen bond move to form a triple-bond (an alkyne ).
Isomerization involves transforming a molecule so that it adopts a different structural conformation; proline isomerization plays an integral role in the modification of histone tails. [36] Fpr4 is the prolyl isomerase enzyme (PPIase) which converts the amino acid proline (P) on histones between the cis and trans conformations .
For example, in the cyclic alcohol inositol (a six-fold alcohol of cyclohexane), the six-carbon cyclic backbone largely prevents the hydroxyl and the hydrogen on each carbon from switching places. Therefore, one has different configurational isomers depending on whether each hydroxyl is on "this side" or "the other side" of the ring's mean plane.
This article needs attention from an expert in biochemistry.The specific problem is: someone with a solid grasp of the full scope of this subject and of its secondary and advanced teaching literatures needs to address A, the clear structural issues of the article (e.g., general absence of catabolic biosynthetic pathways, insertion of macromolecule anabolic paths before all building blocks ...
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 ...