IMPORT AND METABOLISM OF GLUTATHIONE BY STREPTOCOCCUS-MUTANS

Glutathione (gamma-GluCysGly, GSH) is not found in most gram-positive bacteria, but some appear to synthesize it and others, including Strep tococcus mutans ATCC 33402, import it from their growth medium, Import of oxidized glutathione (GSSG) by S. mutans 33402 in 7H9 medium was s hown to require glucose and to occur with an apparent K-m of 18 +/- 5 mu m. GSSG, GSH, S-methylglutathione, and homocysteine-glutathione mix ed disulfide (hCySSG) were imported at comparable rates (measured by d epletion of substrate in the medium), as was the disulfide of gamma-Gl uCys. In contrast, the disulfide of CysGly was not taken up at a measu rable rate, indicating that the gamma-Glu residue is important for eff icient transport, During incubation with GSSG, little GSSG was detecte d in cells but GSH and gamma-GluCys accumulated during the first 30 mi n :Ind then declined, No significant intracellular accumulation of Cys or sulfide was found, Transient intracellular accumulation of D/L-hom ocysteine, as well as GSH and gamma-GluCys, was observed during import of hCySSG, Although substantial levels of GSH were found in cells whe n S. mutans was grown on media containing glutathione, such GSH accumu lation had no effect on the growth rate, However, the presence of cell ular GSH did protect against growth inhibition by the thiol-oxidizing agent diamide, Import of glutathione by S. mutans ATCC 25175, which li ke strain 33402 does not synthesize glutathione, occurred at a rate co mparable to that of strain 33402, but three species which appear to sy nthesize glutathione (S. agalactiae ATCC 12927, S. pyogenes ATCC 8668, and Enterococcus faecalis ATCC 29212) imported glutathione at negligi ble or markedly lower rates.