Cystathionine in rat brain: catabolism in vivo

The content of cystathionine was measured in 35 rat brains; the range was 10-120 nmol/g wet weight and thus the variability of cystathionine content in rat brain was emphasized. The regional distribution of cystathionine was also determined: the highest level was found in cerebellum; the lowest level was observed in the white and gray matter of the hemispheres. These results are different from those obtained in other species. The radioactive metabolites formed from L-(35S)cystathionine injected intracisternally were measured in brains of rats killed at the following times after injection: 0.25, 1, 2, 4,6, 9, 16, and 27 hr. The radioactivity was found both in the proteins and in the acid-soluble fraction. In the acid-soluble fraction the radioactivity was found in various ninhydrin-reacting compounds: [cysteic cysteine sulfinic] acid, taurine, reduced and oxidized glutathione, cystine, cystathionine, and a compound tentatively identified as the mixed disulfide of cysteine and glutathione. The radioactivity of cystathionine decreased exponentially between the 1st and the 27th hour after injection and its half-life was estimated to be about 5 hr. The radioactivity in the other ninhydrin-reacting compounds increased until the 9th hour after injection, then decreased. Half of this radioactivity was present in reduced glutathione, the rest being shared equally between: [cysteic cysteine sulfinic] acid, taurine, and the mixed disulfide. It is worthwhile to note that the radioactivity in the cystine fraction was always very low.