An isomerase enzyme, epimerase catalyzes the stereochemistry inversion within biological chemicals. They configure an asymmetric carbon atom from a substrate which has more than one center for asymmetry and forms interconverting epimers.
One particular mechanism involves inverting the configuration of a 4’hydroxl group of UDP-galactose. This is completed through a series of four steps. Once bound the conserved tyrosine residue within the active site, then removes a proton from the 4’ hydroxyl group.
As well as this, the 4’hydrid is added to the particular si-face for NAD+. After this, the NADH, as well as the 4-ketopryranose intermediate, are generated. This then rotates one hundred and eighty degrees around the pyrophosphorylase atom which presents the opposite face of the ketopyranose intermediate. Once this is complete a hydride moves from NADH to the other face and inverts the 4’ center stereochemistry. During this stage, the conserved tyrosine donates a proton which allows for the regeneration of the 4’ hydroxyl group.
Epmierase can also catalyze the conversion of UDP-GicNAc to UDP-GalNAC is a reverse process. This occurs through a completely identical mechanism with the stereochemical configured from the sugars 4’ hydroxyl group.
In the human body, epimerase has a wide range of interactions. This includes the breakdown of several amino acids such as valine, isoleucine, methionine and alanine. It also interacts with UDP-glucose 4-epimerase. This is used in the final phase of galactose metabolism. It catalyzes UDP-galactose to UDP-glucose which is a reversible conversion process.
Epimierases function as part of crucial metabolic pathways. This does include the Leloir pathway which is where the conversion from galactose to glucose-1 phosphate occurs. Furthermore, bacterial epimerase are also involved with the creation of complex carbohydrate polymers. These are used in the cell walls and are known as potential targets for therapy during the treatment of a bacterial infection. There are various different groups of epimerase enzymes and they each have a unique function. Some are reliant on a permanent keto group while others eliminate nucleotide before adding it once more. Some reform carbon-carbon bonds and certain others cyclize and linearise the pyranose ring. As such, there are a variety of different biochemical processes within what is often determined to be a simple reaction.
As there are numerous different types of epimerase enzymes, they all have individual structures. One example is UDP-galactose 4-epimerase dimer. This is from E. coli and the substrate DP-glucose as well as the cofactor NAD- can be seen bound within the active site. It functions as a homopentamer and there are five monomers arranged in a particular ring.
These catalytic triad residues that are seen and discovered in GALE are also found in AGME. With similar positions structurally, this has analogous functions. There is also the GMER dimer with NADPH bound. Again, the catalytic triad residues are present in GMER and they complete the reduction form of the enzyme.
Each monomer within GALE consists of 348 as well as 338 amino acids. There is also one molecule of NAD. This is tightly bound with a syn-conformation and the s-face is positioned towards a sugar substrate.