470
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
minutes destroys nearly 90% of the oxidase activity but hardly affects the
mutarotase. In fact, the two enzymes can be physically separated by
ammonium sulfate fractionation and differential adsorption on calcium
phosphate gel. The activity of mutarotase is unusually high. Its catalytic
coefficient, 2 X 10
5 min.
-1 , is higher than the coefficient of hydroxyl ion,
8.8 X 10
3 . The latter is one of the most active nonenzymatic catalysts
known for mutarotation (246).
Glucose oxidase has been also found in the red alga Irridophycus
(247), in Pseudomonas fluorescens (55), and in Azotobacter vinelandii
(248). The latter is especially interesting. The oxidation of glucose
catalyzed by a partially purified particulate fraction from A. vinelandii
accumulates D-glucono-8-lactone almost quantitatively even in the absence of a lactone trapping agent. However, the nature of the prosthetic
group of the enzymes from the alga and the pseudomonad has still not
been clearly shown.
Glucose dehydrogenase was first found in the acetone powder of
mammalian liver (249, 250). Even the most potent sample of the
original preparations (251) is far from pure, since it slowly reacts with
methylene blue. An earlier claim that DPN is the coenzyme (252) has
been disputed by Das, who has found both DPN and TPN effective
(253). Work on purification has also been done by Wainio and coworkers (254, 255). However, Brink (222) and Strecker and Korkes
(221) have done the most extensive characterization. More recently it
has been found that the purified preparation can use either pyridine
nucleotide as coenzyme. The Michaelis constant of the glucose dehydrogenase from liver for TPN is smaller than that for DPN.
The H from C-l of glucose is directly transferred to the 4 position
of the nicotinamide of DPN. Like other dehydrogenases the enzyme
also exhibits stereospecificity of the /Mype; it involves the hydrogen
transfer to the opposite side of the ring from that utilized in the reactions
by yeast alcohol dehydrogenase and muscle lactic dehydrogenase or
wheat germ malic dehydrogenase (256, 257, 258). In contrast to liver
alcohol dehydrogenases, the absorption maximum of DPNH at 340 πΐμ
does not shift to 325 πΐμ when it is linked with apoenzyme (259). In
addition to glucose, the enzyme also catalyzes the oxidation of Dgalactose, D- and L-xylose, and D-arabinose (260). Liver glucose dehydrogenase is strongly and competitively inhibited by glucose-6-phosphate
or fructose-l,6-diphosphate. The inhibition constant (K;) for the diphosphate is 6.2 X 10
5 M, and that for G-6-P is 2.5 X 10
6 M (259).
The physiological function of glucose dehydrogenase is obscure.
Brink has suggested (222) that the oxidation of glucose to gluconic
acid (catalyzed by this enzyme) is not a normal metabolic pathway of
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
minutes destroys nearly 90% of the oxidase activity but hardly affects the
mutarotase. In fact, the two enzymes can be physically separated by
ammonium sulfate fractionation and differential adsorption on calcium
phosphate gel. The activity of mutarotase is unusually high. Its catalytic
coefficient, 2 X 10
5 min.
-1 , is higher than the coefficient of hydroxyl ion,
8.8 X 10
3 . The latter is one of the most active nonenzymatic catalysts
known for mutarotation (246).
Glucose oxidase has been also found in the red alga Irridophycus
(247), in Pseudomonas fluorescens (55), and in Azotobacter vinelandii
(248). The latter is especially interesting. The oxidation of glucose
catalyzed by a partially purified particulate fraction from A. vinelandii
accumulates D-glucono-8-lactone almost quantitatively even in the absence of a lactone trapping agent. However, the nature of the prosthetic
group of the enzymes from the alga and the pseudomonad has still not
been clearly shown.
Glucose dehydrogenase was first found in the acetone powder of
mammalian liver (249, 250). Even the most potent sample of the
original preparations (251) is far from pure, since it slowly reacts with
methylene blue. An earlier claim that DPN is the coenzyme (252) has
been disputed by Das, who has found both DPN and TPN effective
(253). Work on purification has also been done by Wainio and coworkers (254, 255). However, Brink (222) and Strecker and Korkes
(221) have done the most extensive characterization. More recently it
has been found that the purified preparation can use either pyridine
nucleotide as coenzyme. The Michaelis constant of the glucose dehydrogenase from liver for TPN is smaller than that for DPN.
The H from C-l of glucose is directly transferred to the 4 position
of the nicotinamide of DPN. Like other dehydrogenases the enzyme
also exhibits stereospecificity of the /Mype; it involves the hydrogen
transfer to the opposite side of the ring from that utilized in the reactions
by yeast alcohol dehydrogenase and muscle lactic dehydrogenase or
wheat germ malic dehydrogenase (256, 257, 258). In contrast to liver
alcohol dehydrogenases, the absorption maximum of DPNH at 340 πΐμ
does not shift to 325 πΐμ when it is linked with apoenzyme (259). In
addition to glucose, the enzyme also catalyzes the oxidation of Dgalactose, D- and L-xylose, and D-arabinose (260). Liver glucose dehydrogenase is strongly and competitively inhibited by glucose-6-phosphate
or fructose-l,6-diphosphate. The inhibition constant (K;) for the diphosphate is 6.2 X 10
5 M, and that for G-6-P is 2.5 X 10
6 M (259).
The physiological function of glucose dehydrogenase is obscure.
Brink has suggested (222) that the oxidation of glucose to gluconic
acid (catalyzed by this enzyme) is not a normal metabolic pathway of