35epimerase

The 35epimerase is an enzyme class described to catalyze epimerization at carbon-3 and/or carbon-5 of carbohydrate substrates. The name reflects the stereochemical centers involved. It is not a widely used term in standard catalogs, but may appear in discussions of sugar epimerization.

Mechanism: Epimerization typically proceeds via deprotonation-reprotonation at the target carbon, often aided by conserved catalytic residues. Some sugar epimerases operate through transient oxidation to a keto intermediate followed by reduction, sometimes requiring cofactors such as NAD+/NADH or metal ions. The exact mechanism varies among family members and substrates.

Substrates and scope: Most proposed 35epimerases would act on monosaccharides or nucleotide-activated sugars (such as UDP- or GDP-sugars) and alter the configuration at C3 and/or C5, generating epimers that differ in hydroxyl orientation and stereochemistry. The products can influence the biosynthesis of polysaccharides, glycoconjugates, or cell wall components.

Biological role: Such enzymes, if present, would contribute to sugar diversity and metabolic flexibility, aiding organisms in producing distinct glycans or adjusting flux through sugar biosynthetic pathways. Known examples of individual 3- or 5-epimerases are documented in various organisms, illustrating the plausibility of combined 3/5 activity.

Nomenclature and status: As of now, there is no standard, widely accepted enzyme formally named "35epimerase." If identified, family members would be characterized by substrate specificity, reaction mechanism, structure, and physiological role, and assigned standard gene and protein names.

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