D-Fructose Dehydrogenase

Related Reading

Fructose is a familiar monosaccharide, which is isomers with glucose. In nature, it exists in many fruits, honey and some compositae plants. Fructose has its own unique properties, its natural high sweetness is unmatched by other sugars, and fructose does not cause dental caries after eating. These characteristics make it very widely used in industrial production. At present, many fructose processing containing different forms food is popular in the market, such as carbonated, fruit juice drinks, etc., and fructose as a food additive has been increasingly used in food processing. In the production of food and beverages, fructose, glucose, sucrose, and lactose are currently the four commonly used nutritive sweeteners. In the past two decades, the use of fructose has increased from 20% by ten percent. It occupies an important position in the market. In addition, crystalline fructose with high purity and good stability is gradually being developed and applied in many industries. Its market demand is considerable and it has broad application prospects.

Figure 1. Structure of fructose.

Features

• Fructose is mainly catalyzed by fructokinase to produce fructose monophosphate in the liver, kidney and small intestine.
• In the body, fructose can be converted into glucose or synthesized glycogen; but glucose and glycogen cannot be reversely converted into fructose.
• Causal fructose can bypass the rate-limiting enzyme (phosphofructokinase) in glycolysis, and in the liver, fructose decomposes faster than glucose.
• The intensity of fructose metabolism depends on the concentration of fructose and is not affected by insulin. The intake and absorption of fructose will not cause hypoglycemia.

D-Fructose Dehydrogenase

In enzymology, fructose 5-dehydrogenase is an enzyme that catalyzes chemical reactions.

D-fructose + receptor→5-dehydro-D-fructose + reducing receptor

Therefore, the two substrates of the enzyme are D-fructose and the receptor, while its two products are 5-dehydro-D-fructose and the reduced receptor. This enzyme belongs to the family of oxidoreductases, especially those that act on the CH-OH group of the donor together with other acceptors. The systematic name of this enzyme class is D-fructose: receptor 5-oxidoreductase. Other commonly used names include fructose 5-dehydrogenase (acceptor), D-fructose dehydrogenase and D-fructose: (acceptor) 5-oxidoreductase.

Properties

• Homogeneity.

The enzyme shows a symmetrical sedimentation peak with an apparent sedimentation constant of 5.8 S in the presence of 1%Triton X-100 in 20-fold diluted Mcllvaine buffer, pH 6.0. Gel filtration alsoshows a symmetrical elution peak of protein coincident with enzyme ac-tivity when analyzed by a column of Sephadex G-200 (1 x 115 cm) thathas been equilibrated with 20-fold diluted buffer, pH 6.0, containing 0.1%Triton X-100 and 1 mM 2-mercaptoethanol. The apparent molecularweight was 140,000 by gel filtration. For the estimation of purity andhomogeneity of the enzyme, the use of a conventional polyacrylamide gelelectrophoresis is not recommended. The purified enzyme dissociates intosubunit components during gel electrophoresis and gives three protein bands.

• Absorption Spectra.

The purified D-fructose dehydrogenase has a cytochrome c-like absorption spectrum. A partially reduced hemoprotein is present in the enzyme preparation, suggesting that the hemoprotein is more autoxidizable when compared with heme c in alcohol dehydrogenase of acetic acid bacteria. Absorption maxima at 553- 550nm, 523 nm, and 417 nm are observed for the reduced enzyme, and a single peak at 409 nm is observed for the oxidized enzyme.

• Catalytic Properties.

The D-fructose dehydrogenase can be assayed in vitro in the presence of any one of the following dyes as an electron acceptor: potassium ferricyanide, phenazine methosulfate, nitro blue tet-razolium, or 2,6-dichlorophenolindophenol, NAD, NADP, or oxygen are completely inactive as electron acceptors. This finding applies to other membrane-bound dehydrogenases.

Reference

1. Ameyama M; Adachi O. D-Fructose dehydrogenase from Gluconobacter industrius, membrane-bound. Methods in Enzymology. 1982, 89: 154–159.