McLaggan D, Logan T M, Lynn D G, Epstein W
Department of Molecular Genetics, University of Chicago, Illinois 60637.
J Bacteriol. 1990 Jul;172(7):3631-6. doi: 10.1128/jb.172.7.3631-3636.1990.
Accumulation of K+ ions and glutamate plays a primary role in maintaining osmotic balance in Escherichia coli, as illustrated by the high concentrations of these ions present in cells growing in medium of high osmolality. We found that two gamma-glutamyl peptides and glutamine also accumulated during growth at high osmolarity. In a mutant unable to make trehalose growing in 1.3 osM medium, glutathione, gamma-glutamylglutamine, and glutamine accumulated to levels of 73, 33, and 140 mumol/g of protein, respectively. In such cells, K+ was present at 1,450 mumol/g of protein, indicating that glutathione and gamma-glutamylglutamine accounted for less than 10% of the low-molecular-weight anions accumulated with K+. However, glutathione is needed for wild-type osmotolerance in this species. A mutant deficient in glutathione because of an insertion in the gshA gene was unable to grow above 1.4 osM, grew more slowly at intermediate osmolarities, and took longer to adapt to growth following osmotic upshock. The involvement of glutathione in osmoregulation was independent of the effect of glutathione on K+ retention.
钾离子和谷氨酸的积累在维持大肠杆菌的渗透平衡中起主要作用，在高渗培养基中生长的细胞中这些离子的高浓度就说明了这一点。我们发现，在高渗透压下生长期间，两种γ-谷氨酰肽和谷氨酰胺也会积累。在无法合成海藻糖且在1.3 osM培养基中生长的突变体中，谷胱甘肽、γ-谷氨酰谷氨酰胺和谷氨酰胺分别积累到73、33和140 μmol/g蛋白质的水平。在这类细胞中，钾离子以1450 μmol/g蛋白质的含量存在，这表明谷胱甘肽和γ-谷氨酰谷氨酰胺占与钾离子一起积累的低分子量阴离子的比例不到10%。然而，谷胱甘肽是该物种野生型渗透压耐受性所必需的。由于gshA基因插入而缺乏谷胱甘肽的突变体在高于1.4 osM的环境中无法生长，在中等渗透压下生长较慢，并且在渗透压升高后需要更长时间才能适应生长。谷胱甘肽参与渗透调节与谷胱甘肽对钾离子保留的影响无关。
