The glucose dehydrogenase was purified from acetone powder of cattle liver. The enzymatic activity was estimated spectrophotometrically by following the increase of the optical density at 340 mμ, the reduction of the coenzyme of the glucose dehydrogenase, in the reaction mixture, which consists of enzyme, DPN and glucose. However, the increment of the absorption could not be attained when glucose had been substituted for glucose oxime, indicating that oxime could not be dehydrogenated by the glucose dehydrogenase. Furthermore, the enzymatic formation of DPNH by the glucose-glucose dehydrogenase system did not be influenced by addition of glucose oxime, pyruvate oxime and hydroxylamine. However, the rate of the reaction was suppressed by the extract of acetone precipitate from fowl liver and this inhibition was recovered by hydroxylamine. In connection with the similar procedure of the spectrophotometric estimation of the enzymatic oxidation and reduction of oxime, deviced in our laboratory, some supplementary experiments were carried out concerning the effect of buffers and that of the concentration of glucose upon the glucose dehydrogenase. Thus, it was established that, even when glucose oxime had been used in those cases, the variation of the extinction at 340 mμ was attributed to oxime itself, which receive and donate the electron, but not to the glucose-glucose dehydrogenase system probably contaminated. Then, the carboxylase was prepared from baker's yeast and its activity was assayed with a Warburg manometer by determining the amounts of carbon dioxide liberated from pyruvate. In this case too, pyruvate oxime as well as α-keteglutarate was not effective as the substrate of this carboxylase preparation in place of pyruvic acid. Furthermore, the decarboxylation from pyruvate did not be influenced by several oximes of pyruvic acid, α-ketoglutaric acid, acetone and glucose. In contrast with the case of the glucose dehydrogenase, however, the evolution of carbon dioxide was repressed by hydroxylamine, although the initial rate of the decarboxylation did not be inhibited and the time until the end of the reaction was almost the same with and without hydroxylamine. Therefore, the inhibition might be ascribed to the decrease of pyruvate, the enzyme substrate, on account of the formation of oxime. These phenomena were also observed with the raw extract of yeast. Thus, it was suggested that, as a result of the formation of oxime, the ability of glucose and pyruvic acid as the enzyme substrate of the respective relevant enzyme was lost and consequently, in relation to the activation of the oximase and the transoximase, the disturbance of the metabolisms in cell might be brought about.