Buurman E T, Boiardi J L, Teixeira de Mattos M J, Neijssel O M
Department of Microbiology, University of Amsterdam, The Netherlands.
Arch Microbiol. 1990;153(5):502-5. doi: 10.1007/BF00248434.
Magnesium-limited chemostat cultures of Klebsiella pneumoniae NCTC 418 with 20 microM CaCl2 in the medium showed a low rate of gluconate plus 2-ketogluconate production relative to potassium- or phosphate-limited cultures. However, when the medium concentration of CaCl2 was increased to 1 mM, the glucose dehydrogenase (GDH) activities also increased and became similar to those observed in potassium- or phosphate limited cultures. It is concluded that this is due to Mg2+ and Ca2+ ions being involved in the binding of pyrroloquinoline quinone (PQQ) to the GDH apoenzyme. There seems to be an absolute requirement of divalent cations for proper enzyme functioning and in this respect Ca2+ ions could replace Mg2+ ions. The high GDH activity which has been found in cells grown under Mg2(+)-limited conditions in the presence of higher concentrations of Ca2+ ions, is compatible with the earlier proposal that GDH functions as an auxiliary energy generating system involved in the maintenance of high transmembrane ion gradients.
在培养基中含有20微摩尔氯化钙的情况下，肺炎克雷伯菌NCTC 418的镁限制恒化器培养物相对于钾限制或磷限制培养物而言，葡糖酸盐加2-酮葡糖酸盐的产生速率较低。然而，当培养基中氯化钙的浓度增加到1毫摩尔时，葡萄糖脱氢酶（GDH）的活性也增加了，并且变得与在钾限制或磷限制培养物中观察到的活性相似。得出的结论是，这是由于镁离子和钙离子参与了吡咯喹啉醌（PQQ）与GDH脱辅酶的结合。似乎二价阳离子对于酶的正常功能是绝对必需的，在这方面钙离子可以替代镁离子。在存在较高浓度钙离子的情况下，在镁离子限制条件下生长的细胞中发现的高GDH活性，与早期提出的GDH作为参与维持高跨膜离子梯度的辅助能量产生系统的提议相一致。
