The intracellular ratio of cysteine and cystine in various tissues

Abstract

1. The cysteine–cystine ratio was measured in rat kidney cortex, diaphragm, jejunum, liver and brain. 2. This ratio was determined by incubating these tissues in buffer containing [³⁵S]cystine and then homogenizing the tissue in a buffered solution of N-ethylmaleimide. The products of this reaction were separated by high-voltage electrophoresis and the radioactivity in the cystine and 2-(l-2′-amino-2′-carboxyethylthio)-N-ethylsuccinimide regions was determined. 3. In these tissues cyst(e)ine was mainly present in the reduced form. 4. After incubation of [³⁵S]cystine with rat jejunal segments it was found that 36% of the cystine in the medium has been reduced. 5. Anaerobiosis, Na⁺-free media, glucose and high concentrations of cystine and lysine were found not to affect significantly the cysteine–cystine ratio in rat kidney-cortex slices.