Cysteine-induced changes of low molecular sulfhydryl/disulfide ratio in rat lymphoid cells

Changes in total protein and nonprotein sulfhydryl content, cell membrane sulfhydryls and mitogen response were examined after incubation of rat lymphoid cells with L-cysteine. Distribution of 35S L-cysteine within the metabolic pool of low molecular thiols and protein thiols was determined by quantitative analysis of metabolites of the oxidative taurine pathway, glutathione, mixed disulfides and protein-associated radioactivity. Significant, incubation time-dependent increase of [3H] thymidine, [3H] uridine and [14C] leucine incorporation was observed in cysteine-preincubated, PHA-stimulated lymph node cells. Subsequent inhibition of PHA-response of lymphocytes and a marked increase of intracellular content of free (reduced form) cysteine was observed as a result of constant supply of cysteine into cells from the incubation medium. Maintenance of [35S] L-cysteine, transported into thymocytes within 3 hours, mainly in -SH form, was dependent on the constant presence of cysteine in the medium and slightly dependent on its concentration (0.01-10 mM). Cysteine catabolites of the oxidative taurine pathway, i.e. taurine, cysteinesulfinic acid and cysteic acid, as well as glutathione, low molecular mixed disulfides, protein cysteine mixed disulfides and proteinincorporated cysteine increased proportionally to the time of cysteine uptake but not to the increasing amounts of intracellular free cysteine. These results support the hypothesis of changed-SH/SS equilibrium of low molecular thiols due to the presence of high amounts of free cysteine, reflecting cell metabolism and functions.