Escherichia coliによる酢酸酸化の適応過程における酸化速度と基質透過

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1.The rate of acetate oxidation by E.coli K12 could be determined by the initial acetate concentration at various levels.The rates, once determined initially, were maintained at constant levels, independent of the decreasing external substrate concentration, until the acetate concentration became extremely low (e.g. 5×10^<-6>M). Such a conspicuous phenomenon has already been reported with Saccharomyces cerevisiae and Escherichia freundii.2. The result of an acetate uptake experiment using ^<14>C-acetate indicated that there is a positive correlation between the rate of acetate oxidation and the rate acetate uptake.In an experiment with initial acetate concentration lower than 5×10<-6>M, it was observed that the decrease of the external substrate concentration results in the lowering of the acetate oxidation rate.Tha above results indicate strongly that the previously postulated carrier molecule, having a very high affinity (Michaelis constant, 2×10<-7>M) for acetate, controls the rate of acetate uptake.3. The Michaelis constant of the acetokinase of this strain, which is known as the acetateterminal enzyme in acetate oxidation, was estimated to be 6×10<-2>M. Therefore it is impossible to consider that this enzyme controls the rate of acetate oxidation.4. The acetate oxidation activity could be increased adaptively using acetate as the inducer.No change in the pattern of acetate oxidation reported above was observed during the process of adaptation. The value of the saturation constant(5×10<-4>M)in the Monodtype equation, which express the relation between the initial substrate concentration and the rate of substrate oxidation, was not changed in the course of acetate adaptation, indicating that the rate-limiting step of acetate oxidation is not altered by acetate adaptation.5. During the acetate adaptation, the activity of monochloroacetate uptake was increased adaptively and the rate of acetate oxidation correlated positively to the rate of monochloroacetate uptake.On the other hand, no increase in the specific activities of acetokinase and phosphotransacetylase was observed. These results imply that the adaptive increase in the acetate oxidation rate as well as the acetate uptake rate might be caused by an increase in the carrier molecules which play an important role in the active transport of acetate.Chloramphenicol inhibited the adaptive increase in the acetate oxidation rate, indicating that the carrier molecule is of proteinaceous nature.
社団法人日本生物工学会の論文
1972-11-25

Escherichia coliによる酢酸酸化の適応過程における酸化速度と基質透過

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