9. SACCHARIDES: ALTERNATE ROUTES OF METABOLISM
473
where E, G, P, T and TH 2 are for the dehydrogenase, glucose, gluconolactone (product), oxidized and reduced TPN, respectively. Thus it is
similar to the reaction of yeast alcohol dehydrogenase (280) and
creatine phosphokinase (281) rather than that of liver alcohol dehydrogenase extensively studied by Theorell and Chance (282, 283). Using
the technique similar to that developed by Dixon (284), the extrapolation of kinetic constants determined at different acidities suggests that
both pK values of EGT and E are slightly higher than 7.0.
In comparing the properties of glucose oxidase, on the one hand, and
glucose dehydrogenase as well as enzymes for the pentose cyclic oxidation of glucose on the other, several important but cryptic facts may be
pointed out.
The particulate glucose oxidase can use 2,6-dichlorophenolindophenol
to replace oxygen as electron acceptor. Triphenyltetrazolium chloride or
methylene blue are practically inactive. This enzyme does not contain
pyridine nucleotide. Its niacin content by the most rigid and sensitive
tests gives a negative value. The particulate preparation, which has the
full glucose oxidase activity, also contains flavin and practically all the
cytochromes in the organism. Very recently Iwasaki (285) has confirmed our results in the oxidation behavior of glucose in this organism,
but he apparently did not fully appreciate the concept of multiple
catabolic pathways of glucose. Although our preparation catalyzes the
decomposition of hydrogen peroxide, neither the rate of the oxidation
nor the total amount of oxygen is changed by addition of ethanol, high
concentrations of acetate or crystalline catalase (286). These results
may point to water rather than hydrogen peroxide as the primary product. Moreover, under anaerobic conditions glucose reduces immediately
all the cytochromes in the preparation, as sodium dithionate does. Although the behavior of flavin in the glucose oxidation catalyzed by the
particulate preparation has not been extensively studied, these findings
indicate that the mode of this oxidation differs from that of the mold
oxidase. On the other hand, the pattern is very close to particulate succinic oxidase such as that in the Keilin-Hartree preparation. This
organism cannot oxidize succinic acid. It may well be that glucose
takes the place of succinic acid in relation to the occurrence of a "twin
headed" (glucose and DPNH) respiratory chain, similarly to succinic
and DPNH in mammals.
Another property that merits discussion is the effect of pH upon the
enzymatic activity. The optimum pH value for glucose oxidase is 5.5. At
acid pH ranges the reduced cytochrome spectra in the particulate
preparation can hardly be demonstrated in aerobic conditions because
the reduced cytochromes are rapidly oxidized by molecular oxygen. On
the other hand, at pH 8.0, the reduced spectrum from glucose does not
473
where E, G, P, T and TH 2 are for the dehydrogenase, glucose, gluconolactone (product), oxidized and reduced TPN, respectively. Thus it is
similar to the reaction of yeast alcohol dehydrogenase (280) and
creatine phosphokinase (281) rather than that of liver alcohol dehydrogenase extensively studied by Theorell and Chance (282, 283). Using
the technique similar to that developed by Dixon (284), the extrapolation of kinetic constants determined at different acidities suggests that
both pK values of EGT and E are slightly higher than 7.0.
In comparing the properties of glucose oxidase, on the one hand, and
glucose dehydrogenase as well as enzymes for the pentose cyclic oxidation of glucose on the other, several important but cryptic facts may be
pointed out.
The particulate glucose oxidase can use 2,6-dichlorophenolindophenol
to replace oxygen as electron acceptor. Triphenyltetrazolium chloride or
methylene blue are practically inactive. This enzyme does not contain
pyridine nucleotide. Its niacin content by the most rigid and sensitive
tests gives a negative value. The particulate preparation, which has the
full glucose oxidase activity, also contains flavin and practically all the
cytochromes in the organism. Very recently Iwasaki (285) has confirmed our results in the oxidation behavior of glucose in this organism,
but he apparently did not fully appreciate the concept of multiple
catabolic pathways of glucose. Although our preparation catalyzes the
decomposition of hydrogen peroxide, neither the rate of the oxidation
nor the total amount of oxygen is changed by addition of ethanol, high
concentrations of acetate or crystalline catalase (286). These results
may point to water rather than hydrogen peroxide as the primary product. Moreover, under anaerobic conditions glucose reduces immediately
all the cytochromes in the preparation, as sodium dithionate does. Although the behavior of flavin in the glucose oxidation catalyzed by the
particulate preparation has not been extensively studied, these findings
indicate that the mode of this oxidation differs from that of the mold
oxidase. On the other hand, the pattern is very close to particulate succinic oxidase such as that in the Keilin-Hartree preparation. This
organism cannot oxidize succinic acid. It may well be that glucose
takes the place of succinic acid in relation to the occurrence of a "twin
headed" (glucose and DPNH) respiratory chain, similarly to succinic
and DPNH in mammals.
Another property that merits discussion is the effect of pH upon the
enzymatic activity. The optimum pH value for glucose oxidase is 5.5. At
acid pH ranges the reduced cytochrome spectra in the particulate
preparation can hardly be demonstrated in aerobic conditions because
the reduced cytochromes are rapidly oxidized by molecular oxygen. On
the other hand, at pH 8.0, the reduced spectrum from glucose does not