The activity of liver cystathionase (EC 4.4.1.1) was decreased after 3 d of stress induced by surgery. The rate of l-cysteine synthesis from l-methionine was significantly higher in isolated hepatocytes from controls than in hepatocytes from rats suffering from surgical stress. The half-life of l-[2(n)-3H]methionine was significantly higher in rats submitted to surgical stress than in controls. Plasma l-methionine: l-cystine ratio was higher in stressed rats than in controls. l-cystine uptake was significantly increased in the surgically-stressed rats when compared with the controls. All these facts are consistent with the hypothesis that the observed inhibition of cystathionase is physiologically important and thatl-cysteine might be considered as an essential amino acid in cases of surgical stress.
