9. SACCHARIDES: ALTERNATE ROUTES OF METABOLISM
475
workers (274, 300). They have isolated two soluble and one particulate
enzyme from cell-free preparations of A. suboxydans. Both soluble enzymes are TPN-specific in catalyzing the oxidation of gluconate to
2-ketogluconate and 5-ketogluconate, respectively. They are named
2-ketogluconate reductase and 5-ketogluconate reductase (300). The
particulate enzyme is possibly cytochrome linked and catalyzes the
gluconate oxidation to 2-ketogluconate. 2-Ketogluconate reductase has
been also partially purified from Corynebacterium helvolum, from yeast,
Debaryomyces hansenii, and from the mold Aspergillus nidulans (301).
With extracts of Aerobacter cloacae, DeLey (302, 303) has found
another soluble enzyme, 2-ketogluconokinase, which catalyzes the following reaction (91):
Mg
++
2-Keto-D-gluconic acid + ATP
► 2-Keto-6-phospho-D-gluconic acid + ADP
The product upon hydrolysis yields 2-ketogluconic acid. The Ghent
school in this connection has made an impressive survey on the metabolism of a great number of microorganisms and their ability to form
2-keto-6-phospho-D-gluconic acid by cell-free extracts (304). Table VIII
is adapted from DeLey and Vandamme (304). As can be seen from the
table, a great number of organisms can grow on 2-ketogluconate, but
none tested contains constitutive 2-ketogluconokinase. Some doubt would
thus be cast on the importance of the kinase in normal metabolism
since it is only an inducible enzyme.
The literature in the field is quite diffuse although the scale of studies
by a number of schools is impressive. To date a few hundred organisms
have been scanned for gluconate metabolism. However, even the slightest indication of relationship between the biochemical pattern and the
evolutionary scale cannot be traced out, nor can a general rationalization be gained in spite of the real existence of species specificity. These
facts are true not only with respect to the activities just described, but
also regarding other physiological reactions. One consequently would
wonder whether the tactics of attacks now prevalent and the areas of
reactions chosen are the most profitable or efficient to pursue the
discipline of comparative biochemistry.
D. POLYOL DEHYDROGENASES
Investigations on the biochemical oxidation of polyols were begun as
early as the middle of the nineteenth century. Pelouze (305) fermented
the juice of mountain ash berries in open vessels and obtained an
optically active, crystalline, unknown compound. However, it was not
until 1896-1898 that Bertrand (306) was able to identify the product as
475
workers (274, 300). They have isolated two soluble and one particulate
enzyme from cell-free preparations of A. suboxydans. Both soluble enzymes are TPN-specific in catalyzing the oxidation of gluconate to
2-ketogluconate and 5-ketogluconate, respectively. They are named
2-ketogluconate reductase and 5-ketogluconate reductase (300). The
particulate enzyme is possibly cytochrome linked and catalyzes the
gluconate oxidation to 2-ketogluconate. 2-Ketogluconate reductase has
been also partially purified from Corynebacterium helvolum, from yeast,
Debaryomyces hansenii, and from the mold Aspergillus nidulans (301).
With extracts of Aerobacter cloacae, DeLey (302, 303) has found
another soluble enzyme, 2-ketogluconokinase, which catalyzes the following reaction (91):
Mg
++
2-Keto-D-gluconic acid + ATP
► 2-Keto-6-phospho-D-gluconic acid + ADP
The product upon hydrolysis yields 2-ketogluconic acid. The Ghent
school in this connection has made an impressive survey on the metabolism of a great number of microorganisms and their ability to form
2-keto-6-phospho-D-gluconic acid by cell-free extracts (304). Table VIII
is adapted from DeLey and Vandamme (304). As can be seen from the
table, a great number of organisms can grow on 2-ketogluconate, but
none tested contains constitutive 2-ketogluconokinase. Some doubt would
thus be cast on the importance of the kinase in normal metabolism
since it is only an inducible enzyme.
The literature in the field is quite diffuse although the scale of studies
by a number of schools is impressive. To date a few hundred organisms
have been scanned for gluconate metabolism. However, even the slightest indication of relationship between the biochemical pattern and the
evolutionary scale cannot be traced out, nor can a general rationalization be gained in spite of the real existence of species specificity. These
facts are true not only with respect to the activities just described, but
also regarding other physiological reactions. One consequently would
wonder whether the tactics of attacks now prevalent and the areas of
reactions chosen are the most profitable or efficient to pursue the
discipline of comparative biochemistry.
D. POLYOL DEHYDROGENASES
Investigations on the biochemical oxidation of polyols were begun as
early as the middle of the nineteenth century. Pelouze (305) fermented
the juice of mountain ash berries in open vessels and obtained an
optically active, crystalline, unknown compound. However, it was not
until 1896-1898 that Bertrand (306) was able to identify the product as