グルタミン酸醗酵の酵素レベルでの解析 : (第2報)種々の酵素活性の経時変化と細胞内pH

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The changes in the activities of glutamic dehydrogenase (GDH), isocitric dehydrogenase (ICDH), condensing enzyme (CE), isocitritase (ICT), and malic enzyme (ME) were investigated in the course of glutamic acid fermentation in a culture of Brevibacterium sp. It was shown that none of the specific activities (μ moles substrate reacted/mg dry cell weight/uni time) of the above enzymes varied in response to the transition from the phase of growth (the first phase) to that of product formation (the second phase). Only the time course of ME exhibited a peak, but it was not correlated with the phase transition. It was noteworthy that the specific activity of GDH, which showed no distinct change throughout the culture time, was on the order of ten, one-hundred, and one-thousand times, respectively, as high as the specific activities of CE, ICT, and ICDH; furthermore, the rate of the backward reaction with GDH to form glutamate was six times as high as that of the reaction from glutamate to α-ketoglutarate.For estimating enzyme activities within cells, the values of cell pH were measured either by the "equilibrating pH method" or the "dilution-pH method." THe former method is based on the assumption that no change in the pH of a cell suspension would occur upon sonication in the cold if the pH of the suspending menstruum (very dilute buffer solution) were equal to the cell pH. The latter method consisted in extrapolating the dilution-pH curve of a sonicated cell suspension to zero dilution.The data showed that the cell pH in the second phase (6.9-7.0) was somewhat higher than that in the first phase (6.3-6.6), implying that the pH change favored the activity of GDH in the second phase. The above observation, together with the previously reported result regarding the decreased αKGDH activity in the second phase, is helpful for understanding the cause of the preferential formation of glutamate in this phase.
社団法人日本生物工学会の論文
1971-08-25

グルタミン酸醗酵の酵素レベルでの解析 : (第2報)種々の酵素活性の経時変化と細胞内pH

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