Tryptophan pyrrolase in haem regulation. Experiments with administered haematin and the relationship between the haem saturation of tryptophan pyrrolase and the activity of 5-aminolaevulinate synthase in rat liver

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Abstract
Administration of hematin to rats decreases 5-aminolevulinate synthase activity in whole liver homogenates. An inverse relationship between this decrease and the increase in saturation of apo-(tryptophan pyrrolase) with heme is observed during the initial phase of treatment with hematin. Significant changes in both functions are caused by a 1 mg/kg dose of hematin, whereas the maximum effects are achieved by the 5 mg/kg dose. Prevention by allopurinol of the conjugation of exogenously administered hematin with apo-(tryptophan pyrrolase) renders this heme available for further repression of 5-aminolevulinate synthase. The various aspects of the relationship between synthase activity and the heme saturation of tryptophan pyrrolase are discussed.