CS and acute respiratory distress syndrome: The activity of citrate synthase (CS), the first enzyme in the tricarboxylic acid (TCA) cycle, was reduced in the ALS I group of mice (0.385 ± 0.02 μmol/min/mg of protein), compared with the corresponding WT mice (0.540 ± 0.03 μmol/min/mg of protein) (Figure 2).