9. SACCHARIDES: ALTERNATE ROUTES OF METABOLISM
471
glucose. This is in line with the findings from isotopic studies by Stetten
and Stetten (261), who have concluded that the direct oxidation of
glucose catalyzed by the liver dehydrogenase contributes little, if any,
gluconic acid to the body fluid.
Glucose dehydrogenase has also been found in yeast (262) and in
extracts of Candida reukaufii and Endomyces vernalis (263). However,
the latter uses methylene blue as the acceptor. Further characterization
remains to be done.
In most systems the proposal of a lactone as the first intermediate in
the glucose oxidation is not based on the direct study of the enzymatic
reaction. However, a lactone-splitting enzyme has been studied, and its
purification from yeast has been achieved with at least 36-fold concentration (248). This enzyme has been also found in bacteria, molds, and
mammalian tissues. It requires divalent ions, such as Mg
2+ , Mn
2+ or
Co
2+ for activity. Only those lactones which possess the same configuration as D-glucono-δ-lactone are active. Among the compounds tested
with the purified lactonase only D-glucono-δ -lactone and 6-phosphoglucono-δ-lactone show 100% hydrolysis in 5 minutes; lactobionic-δlactone, D-glucono-y-lactone, and D-galacto-y-lactone are much slower;
whereas D-mannono-δ-lactone, D-xylono-y-lactone, D-glycero-D-galactonoheptono-y-lactone, D-saccharo-δ-, D-gulono-y-, D-glucurono-γ-, D- and
L-arabono-γ-, D-talono-γ-, L-galactono-y-, D-glycero-D-idoheptono-γ-, and
D-glycero-D-galactono-y-lactones, lactide, and pantoyl lactone are inactive. The enzymatic hydrolysis follows the first-order kinetics in contrast
to the nonenzymatic reaction of zero order (248).
B. MULTIPLE CATABOLIC PATHWAYS OF GLUCOSE
IN Acetobacter suboxydans
Acetobacter suboxydans is the one of a few organisms which have
been extensively studied and possess divergent pathways in the oxidation of glucose, as summarized in Fig. 11. This colorful microorganism
was first isolated in 1924 by Kluyver and DeLeeuw (264). Prior to
1952, however, practically all biochemical reactions were studied in
fermentation media or at most with resting cells. Consequently it was
believed that this organism had only a very restricted oxidation capacity;
the yields of sorbose from sorbitol were more than 85%, and there was
nearly quantitative conversion of glycerol to dihydroxyacetone, or of
glucose to gluconic acid. Reviews on earlier work have appeared (265,
266). In 1952, two important techniques for the study of this microorganism were introduced. They are use of 2,4-dinitrophenol, toward
which A. suboxydans shows unusual behavior, and the methods of cellfree preparations (267-273). Since then both methods have been ex-
471
glucose. This is in line with the findings from isotopic studies by Stetten
and Stetten (261), who have concluded that the direct oxidation of
glucose catalyzed by the liver dehydrogenase contributes little, if any,
gluconic acid to the body fluid.
Glucose dehydrogenase has also been found in yeast (262) and in
extracts of Candida reukaufii and Endomyces vernalis (263). However,
the latter uses methylene blue as the acceptor. Further characterization
remains to be done.
In most systems the proposal of a lactone as the first intermediate in
the glucose oxidation is not based on the direct study of the enzymatic
reaction. However, a lactone-splitting enzyme has been studied, and its
purification from yeast has been achieved with at least 36-fold concentration (248). This enzyme has been also found in bacteria, molds, and
mammalian tissues. It requires divalent ions, such as Mg
2+ , Mn
2+ or
Co
2+ for activity. Only those lactones which possess the same configuration as D-glucono-δ-lactone are active. Among the compounds tested
with the purified lactonase only D-glucono-δ -lactone and 6-phosphoglucono-δ-lactone show 100% hydrolysis in 5 minutes; lactobionic-δlactone, D-glucono-y-lactone, and D-galacto-y-lactone are much slower;
whereas D-mannono-δ-lactone, D-xylono-y-lactone, D-glycero-D-galactonoheptono-y-lactone, D-saccharo-δ-, D-gulono-y-, D-glucurono-γ-, D- and
L-arabono-γ-, D-talono-γ-, L-galactono-y-, D-glycero-D-idoheptono-γ-, and
D-glycero-D-galactono-y-lactones, lactide, and pantoyl lactone are inactive. The enzymatic hydrolysis follows the first-order kinetics in contrast
to the nonenzymatic reaction of zero order (248).
B. MULTIPLE CATABOLIC PATHWAYS OF GLUCOSE
IN Acetobacter suboxydans
Acetobacter suboxydans is the one of a few organisms which have
been extensively studied and possess divergent pathways in the oxidation of glucose, as summarized in Fig. 11. This colorful microorganism
was first isolated in 1924 by Kluyver and DeLeeuw (264). Prior to
1952, however, practically all biochemical reactions were studied in
fermentation media or at most with resting cells. Consequently it was
believed that this organism had only a very restricted oxidation capacity;
the yields of sorbose from sorbitol were more than 85%, and there was
nearly quantitative conversion of glycerol to dihydroxyacetone, or of
glucose to gluconic acid. Reviews on earlier work have appeared (265,
266). In 1952, two important techniques for the study of this microorganism were introduced. They are use of 2,4-dinitrophenol, toward
which A. suboxydans shows unusual behavior, and the methods of cellfree preparations (267-273). Since then both methods have been ex-