As an important member of the aldo-keto reductase ( AKR) superfamily，microbial AKRs exist in a wide range of microorganisms and perform oxidoreduction on a broad variety of natural and artificial ketone compounds． Usually，microbial AKRs are monomeric proteins with molecular weights around 37 kDa，containing the typical ( α /β)8-barrel fold and a conserved coenzyme binding domain． All microbial AKRs obey the ordered bi-bi mechanism，driven by a tetrad of Asp-Tyr-Lys-His． Currently，microbial AKRs have been applied in the synthesis of xylitol，vitamin C immediate precursor 2-keto-L-gulonic acid and pharmaceutical intermediate chiral alcohols．