Biochemistry


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0 Q&A 8549 Views Nov 5, 2015
Mannitol is a polyol that occurs in a wide range of living organisms, where it fulfills different physiological roles. Several pathways have been described for the metabolism of mannitol by bacteria, including the phosphoenolpyruvate-dependent phosphotransferase system (PST) and a M2DH-based catabolic pathway. The latter involves two enzymes, a mannitol-2-dehydrogenase (EC 1.1.1.67) and a fructokinase (EC 2.7.1.4), and has been identified in different bacteria, e.g., the marine Bacteroidetes Zobellia galactanivorans (Zg) which had recently gained interest to study the degradation of macroalgal polysaccharides. This protocol describes the biochemical characterization of a recombinant mannitol-2-dehydrogenase (M2DH) of Zobellia galactanivorans. The ZgM2DH enzyme catalyzes the reversible conversion of mannitol to fructose using NAD+ as a cofactor. ZgM2DH activity was assayed in both directions, i.e., fructose reduction and mannitol oxidation.
Reversible reaction:
D-mannitol + NAD+ ↔ D-fructose + NADH + H+
0 Q&A 9316 Views Nov 5, 2015
Mannitol is a polyol that occurs in a wide range of living organisms, where it fulfills different physiological roles. Several pathways have been described for the metabolism of mannitol by bacteria, including the phosphoenolpyruvate-dependent phosphotransferase system (PST) and a M2DH-based catabolic pathway. The latter involves two enzymes, a mannitol-2-dehydrogenase (EC 1.1.1.67) and a fructokinase (EC 2.7.1.4), and has been identified in different bacteria, e.g.,, the marine Bacteroidetes Zobellia galactanivorans (Zg) which had recently gained interest to study the degradation of macroalgal polysaccharides. This protocol describes the biochemical characterization of a recombinant fructokinase (FK) of Zobellia galactanivorans. The ZgFK enzyme catalyzes the conversion of fructose to fructose-6-phosphate using ATP as a cofactor.
[Principle] Fructokinase (FK) activity was determined by an enzyme-coupled assay (Figure 1). ADP formed through the FK reaction, i.e., phosphorylation of fructose to fructose-6-phosphate (F6P), is used by the pyruvate kinase (PK) which transforms phosphoenolpyruvate (PEP) to pyruvate. Then, lactate dehydrogenase (LDH) converts pyruvate to lactate using NADH as a cofactor. FK activity is measured by following the decrease in absorbance at 340 nm which corresponds to the transformation of NADH to NAD+.


Figure 1. Enzyme-coupled reaction used for determination of fructokinase (FK) activity



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