Sherrill C, Fahey R C
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla 92093, USA.
J Bacteriol. 1998 Mar;180(6):1454-9. doi: 10.1128/JB.180.6.1454-1459.1998.
Glutathione (gamma-GluCysGly, GSH) is not found in most gram-positive bacteria, but some appear to synthesize it and others, including Streptococcus mutans ATCC 33402, import it from their growth medium. Import of oxidized glutathione (GSSG) by S. mutans 33402 in 7H9 medium was shown to require glucose and to occur with an apparent Km of 18+/-5 microM. GSSG, GSH, S-methylglutathione, and homocysteine-glutathione mixed disulfide (hCySSG) were imported at comparable rates (measured by depletion of substrate in the medium), as was the disulfide of gamma-GluCys. In contrast, the disulfide of CysGly was not taken up at a measurable rate, indicating that the gamma-Glu residue is important for efficient transport. During incubation with GSSG, little GSSG was detected in cells but GSH and gamma-GluCys accumulated during the first 30 min and then declined. No significant intracellular accumulation of Cys or sulfide was found. Transient intracellular accumulation of D/L-homocysteine, as well as GSH and gamma-GluCys, was observed during import of hCySSG. Although substantial levels of GSH were found in cells when S. mutans was grown on media containing glutathione, such GSH accumulation had no effect on the growth rate. However, the presence of cellular GSH did protect against growth inhibition by the thiol-oxidizing agent diamide. Import of glutathione by S. mutans ATCC 25175, which like strain 33402 does not synthesize glutathione, occurred at a rate comparable to that of strain 33402, but three species which appear to synthesize glutathione (S. agalactiae ATCC 12927, S. pyogenes ATCC 8668, and Enterococcus faecalis ATCC 29212) imported glutathione at negligible or markedly lower rates.
大多数革兰氏阳性细菌中不存在谷胱甘肽（γ-谷氨酰半胱氨酰甘氨酸，GSH），但有些细菌似乎能合成它，而其他细菌，包括变形链球菌ATCC 33402，则从其生长培养基中摄取。已证明变形链球菌33402在7H9培养基中摄取氧化型谷胱甘肽（GSSG）需要葡萄糖，其表观Km为18±5微摩尔。GSSG、GSH、S-甲基谷胱甘肽和同型半胱氨酸-谷胱甘肽混合二硫化物（hCySSG）的摄取速率相当（通过培养基中底物的消耗来测量），γ-谷氨酰半胱氨酸的二硫化物也是如此。相比之下，半胱氨酰甘氨酸的二硫化物摄取速率无法测量，这表明γ-谷氨酰残基对于有效转运很重要。在用GSSG孵育期间，细胞中几乎检测不到GSSG，但GSH和γ-谷氨酰半胱氨酸在前30分钟内积累，然后下降。未发现细胞内半胱氨酸或硫化物有明显积累。在摄取hCySSG期间，观察到D/L-同型半胱氨酸以及GSH和γ-谷氨酰半胱氨酸在细胞内短暂积累。虽然当变形链球菌在含有谷胱甘肽的培养基上生长时，细胞内发现了大量的GSH，但这种GSH积累对生长速率没有影响。然而，细胞内GSH的存在确实能防止硫醇氧化剂二酰胺对生长的抑制作用。与菌株33402一样不合成谷胱甘肽的变形链球菌ATCC 25175摄取谷胱甘肽的速率与菌株33402相当，但三种似乎能合成谷胱甘肽的细菌（无乳链球菌ATCC 12927、化脓性链球菌ATCC 8668和粪肠球菌ATCC 29212）摄取谷胱甘肽的速率可忽略不计或明显较低。
