Monovalent carboxylic ionophores inhibit transport of carbomoyl‐phosphate synthetase I into mitochondria in Reuber hepatoma H‐35 cells and cause accumulation of enzyme precursor

Transport of the precursor for carbamoyl‐phosphate synthetase I into mitochondria in Reuber hepatoma H‐35 cells was inhibited by adding monensin or nigericin to the culture medium at a concentration of 0.5 μM, and the enzyme precursor accumulated, mainly in the cytosolic fraction. Accumulated precursor was degraded slowly with a half‐life of more than 16 min. Valinomycin, nonactin, A23187, X‐537A (lasalocid), bromo‐lasalocid, and carbonyl cyanide m ‐chlorophenylhydrazone did not exhibit these effects at concentrations at which they did not inhibit protein synthesis of the cells.