O'Brien R W, Stern J R
J Bacteriol. 1969 Aug;99(2):389-94. doi: 10.1128/jb.99.2.389-394.1969.
In contrast to the absolute Na(+) requirement for anaerobic growth of Aerobacter aerogenes on citrate as sole carbon source, aerobic growth of this microorganism did not require the presence of Na(+). However, Na(+) (optimal concentration, 10 mm) did increase the maximal amount of aerobic growth by 60%, even though it did not change the rate of growth. This increase in growth was specifically affected by Na(+), which could not be replaced by K(+), NH(4) (+), Li(+), Rb(+), or Cs(+). Enzyme profiles were determined in A. aerogenes cells grown aerobically on citrate in media of varying cationic composition. Cells grown in Na(+)-free medium possessed all the enzymes of the citric acid cycle including alpha-ketoglutarate dehydrogenase, which is repressed by anaerobic conditions of growth. The enzymes of the anaerobic citrate fermentation pathway, citritase and oxalacetate decarboxylase, were also present in these cells, but this pathway of citrate catabolism was effectively blocked by the absence of Na(+), which is essential for the activation of the oxalacetate decarboxylase step. Thus, in Na(+)-free medium, aerobic citrate catabolism proceeded solely via the citric acid cycle. Addition of 10 mm Na(+) to the aerobic citrate medium resulted in the activation of oxalacetate decarboxylase and the repression of alpha-ketoglutarate dehydrogenase, thereby diverting citrate catabolism from the (aerobic) citric acid cycle mechanism to the fermentation mechanism characteristic of anaerobic growth. The further addition of 2% potassium acetate to the medium caused repression of citritase and derepression of alpha-ketoglutarate dehydrogenase, switching citrate catabolism back into the citric acid cycle.
与产气气杆菌在以柠檬酸盐作为唯一碳源进行厌氧生长时对钠离子的绝对需求不同，该微生物的有氧生长并不需要钠离子的存在。然而，钠离子（最佳浓度为10 mM）确实使有氧生长的最大量增加了60%，尽管它并没有改变生长速率。这种生长的增加受到钠离子的特异性影响，钾离子、铵离子、锂离子、铷离子或铯离子都无法替代它。在不同阳离子组成的培养基中，以柠檬酸盐为碳源进行有氧生长的产气气杆菌细胞中测定了酶谱。在无钠离子培养基中生长的细胞拥有柠檬酸循环的所有酶，包括在厌氧生长条件下会被抑制的α-酮戊二酸脱氢酶。厌氧柠檬酸盐发酵途径的酶，柠檬酸酶和草酰乙酸脱羧酶，在这些细胞中也存在，但由于缺乏对草酰乙酸脱羧酶步骤激活至关重要的钠离子，柠檬酸盐分解代谢的这条途径被有效阻断。因此，在无钠离子培养基中，有氧柠檬酸盐分解代谢仅通过柠檬酸循环进行。向有氧柠檬酸盐培养基中添加10 mM钠离子会导致草酰乙酸脱羧酶的激活和α-酮戊二酸脱氢酶的抑制，从而将柠檬酸盐分解代谢从（有氧的）柠檬酸循环机制转向厌氧生长特有的发酵机制。向培养基中进一步添加2%的醋酸钾会导致柠檬酸酶的抑制和α-酮戊二酸脱氢酶的去抑制，使柠檬酸盐分解代谢重新回到柠檬酸循环。
