Sorbitol Dehydrogenase (SDH)

L-iditol:NAD⁺ 5′-oxidoreductase
Sorbitol dehydrogenase (SDH) from sheep liver has a molar mass of 152kDa. The protein is a tetramer of four identical subunits. Each of these subunits has 355 amino acid residues, of which 10 are cysteine residues. Each subunit contains a zinc atom at the active site, which is associated with three protein ligands and a water molecule. The zinc atom associates with the oxygen of the sorbitol hydroxyl or of the fructose carbonyl interconverted during catalysis.

Reduces L-iditol to L-sorbose. Also acts on D-glucitol and other closely related sugar alcohols. Allows the reduction of ketones to polyols (see aldolases for the synthesis of ketoses).

Sorbitol dehydrogenase (SDH) catalyzes the reversible NAD-linked conversion of D-sorbitol to D-fructose and forms a part of the sorbitol pathway, which is a crucial bypass to glycolysis for glucose metabolism. This pathway has been found to be associated with the accumulation of sorbitol in lens, which results in diabetic cataractogenesis. SDH also oxidizes various polyols and other secondary alcohols into their corresponding ketones.

Lyophilizate (60 mg contain 10 mg enzyme protein and 50 mg maltose).

Activator: The reactions (oxidation or reduction) are fastest in Tris or triethanolamine buffer.
Stabilizers: Maltose is used as stabilizer.
Storage conditions (working solution): An aqueous solution is stable at 2 to 8 °C for several weeks.

Store at 2 to 8 °C. (Store the lyophilizate dry.)

Contaminants: <0.01% ADH, <0.02% GIDH and glucose dehydrogenase, each, <0.05% LDH and MDH, each.

For life science research only. Not for use in diagnostic procedures.

One unit (U) sorbitol dehydrogenase will reduce 1 mol of D-fructose in one minute at +25 °C and pH 7.6 [triethanolamine buffer; 150 mM fructose (nonsaturating concentration)]. The above assay consumes 1 mol of NADH per mol of D-sorbitol formed.