Carlsson J, Larsen J T, Edlund M B
Department of Oral Microbiology, University of Umeå, Sweden.
Oral Microbiol Immunol. 1994 Oct;9(5):297-300. doi: 10.1111/j.1399-302x.1994.tb00074.x.
Although fusobacteria use amino acids and peptides as energy source, it is not known whether they are able to actively transport peptides into the cell. In the present study the tripeptide glutathione was used as a model substance to investigate peptide uptake in Fusobacterium nucleatum subsp. nucleatum. Cells harvested after 2 days of growth on blood agar or in their exponential growth phase in broth were suspended in buffer with glutathione, L-cysteinylglycine and L-cysteine. As a measure of cell uptake, the formation of hydrogen sulfide was followed. Cells from blood agar had a low capacity to form hydrogen sulfide from the tripeptide glutathione and the dipeptide L-cysteinylglycine. However, hydrogen sulfide was formed from L-cysteinylglycine, but not from glutathione or from L-cysteine, by cells grown in broth in such a way that it strongly indicated an active transport of L-cysteinylglycine with a Km of 18 microM. Hydrogen sulfide was efficiently formed from glutathione by cells grown in broth in the presence 1 mM glutathione. In these cells a glycylglycine-dependent L-gamma-glutamyl peptidase activity was induced. It is probable that the efficient utilization of glutathione for hydrogen sulfide formation mirrored the uptake of L-cysteinylglycine after an L-gamma-glutamyl peptidase had split L-glutamate off from glutathione.
尽管梭杆菌利用氨基酸和肽作为能量来源，但它们是否能够主动将肽转运到细胞内尚不清楚。在本研究中，三肽谷胱甘肽被用作模型物质，以研究具核梭杆菌具核亚种中的肽摄取情况。在血琼脂上生长2天或在肉汤中处于指数生长期后收获的细胞，悬浮于含有谷胱甘肽、L-半胱氨酰甘氨酸和L-半胱氨酸的缓冲液中。作为细胞摄取的衡量指标，跟踪了硫化氢的形成。来自血琼脂的细胞从三肽谷胱甘肽和二肽L-半胱氨酰甘氨酸形成硫化氢的能力较低。然而，在肉汤中生长的细胞从L-半胱氨酰甘氨酸形成了硫化氢，但从谷胱甘肽或L-半胱氨酸中未形成，这强烈表明L-半胱氨酰甘氨酸存在主动转运，其米氏常数为18微摩尔。在含有1毫摩尔谷胱甘肽的肉汤中生长的细胞能有效地从谷胱甘肽形成硫化氢。在这些细胞中诱导了一种甘氨酰甘氨酸依赖性L-γ-谷氨酰肽酶活性。谷胱甘肽被有效利用来形成硫化氢，这可能反映了在L-γ-谷氨酰肽酶将L-谷氨酸从谷胱甘肽中裂解下来后，L-半胱氨酰甘氨酸的摄取情况。
