The Inhibition of Tryptophan Pyrrolase Synthesis in Rat Liver by Carbon Tetrachloride*

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Abstract
1. Administration of carbon tetrachloride (CCl4, 0.5–2.5 ml/kg body weight) to rats, resulted in decrease in the activity of hepatic tryptophan pyrrolase [L-tryptophan: oxygen oxidoreductase, EC 1. 13. 1. 12] within a few hours. The induction of this enzyme by simultaneous administration of triamcinolone acetonide and L-tryptophan was also markedly suppressed from the first hour after CCl4 treatment. 2. No activator or inhibitor effect was found to participate in this decrease in activity and inducibility of the enzyme. CCl4, at the concentration used did not cause a change in the Km value of pyrrolase or significant release of the enzyme into the blood stream. 3. Measurement of the decrease in enzyme activity after administration of puromycin to CCl4-treated and normal rats, showed that the rates of degradation of pyrrolase in normal and CCl4 treated liver were the same. 4. Actinomycin-mediated superinduction of pyrrolase was inhibited by concomitant administration of CCl4. 5. Pretreatment of rats with aminoacetonitrile reduced the decrease in activity and inducibility of pyrrolase caused by CCl4 while promethazine had no affect. 6. These findings strongly suggest that CCl4 causes decrease in hepatic tryptophan pyrrolase activity and inducibility by disturbance of enzyme synthesis at the translational, rather than the transcriptional step.

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