Cysteine and glutathione metabolism in organ-cultured rat corneas

Abstract

The capability of organ-cultured rat corneas to metabolize cysteine and synthesize glutathione was assessed by use of radioactive L-cyst(e)ine. Metabolites from protein-free tissue extracts were separated and quantified by HPLC, using radioisotope and ultraviolet detectors. Most of the radioactivity detected in the rat cornea was found in three areas of the HPLC elution profile: 1) reduced glutathione, 2) cystine and 3) in a rapidly eluting area (the 'five-minute' area) consisting of several unidentified peaks. The proportion of radioactivity found within the five-minute area increased with time of incubation and became the dominant radioactive peak area by 48 hours of incubation. In contrast to rat lens extracts, the synthesis of glutathione in rat cornea formed a minor portion of the L-cysteine metabolic products. The unlabeled reduced glutathione concentration was relatively stable over a 48-hour incubation period. Synthesis of glutathione was prevented by 0.3 mM buthionine sulfoximine, resulting in more than 90% of the radioactivity being contained in the five-minute peak area. Inhibition of glutathione synthesis allowed the estimation of glutathione's half-life to approximate 10.5 hours in the organ-cultured rat cornea.