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  • Title: Effect of endotoxin on tryptophan pyrrolase and delta-aminolaevulinate synthase: evidence for an endogenous regulatory haem fraction in rat liver.
    Author: Bissell DM, Hammaker LE.
    Journal: Biochem J; 1977 Aug 15; 166(2):301-4. PubMed ID: 911321.
    Abstract:
    Endotoxin was administered to rats at a dose shown previously to stimulate hepatic haem oxygenase activity and to block induction of delta-aminolaevulinate synthase, apparently by causing redistribution of haem from cytochrome P-450 to a regulatory haem pool in the liver. Within 5h of the administration of endotoxin (at a time when the effect of the compound on cytochrome P-450 is maximal) the relative saturation of tryptophan pyrrolase with intrinsic haem rose, from a basal value of 50% to 90%, indicating that 'free' haem had become available. Concurrently, the activity of delta-aminolaevulinate synthase was decreased to 25% of its basal value. Haem oxygenase reached peak activity 13h after endotoxin administration. These findings provide new evidence for the existence of an 'unassigned' hepatic haem fraction, which exchanges with cytochrome P-450 haem and regulates these three enzyme functions.
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