These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Degradation of cytochrome P-450 haem by carbon tetrachloride and 2-allyl-2-isopropylacetamide in rat liver in vivo and in vitro. Involvement of non-carbon monoxide-forming mechanisms.
    Author: Guzelian PS, Swisher RW.
    Journal: Biochem J; 1979 Dec 15; 184(3):481-9. PubMed ID: 120199.
    Abstract:
    Degradation of intrinsic hepatic [(14)C]haem was analysed as (14)CO formation in living rats and in hepatic microsomal fractions prepared from these animals 16h after pulse-labelling with 5-amino[5-(14)C]laevulinic acid, a precursor that labels bridge carbons of haem in non-erythroid tissues. NADPH-catalysed peroxidation of microsomal lipids in vitro (measured as malondialdehyde) was accompanied by loss of cytochrome P-450 and microsome-associated [(14)C]haem (largely cytochrome P-450 haem), but little (14)CO formation. No additional (14)CO was formed when carbon tetrachloride and 2-allyl-2-isopropylacetamide were added to stimulate lipid peroxidation and increase loss of cytochrome P-450 [(14)C]haem. Because the latter effect persisted despite inhibition of lipid peroxidation with MnCl(2) or phenyl-t-butylnitrone(a spin-trapping agent for free radicals), it was concluded that carbon tetrachloride, as reported for 2-allyl-2-isopropylacetamide, may promote loss of cytochrome P-450 haem through a non-CO-forming mechanism independent of lipid peroxidation. By comparison with breakdown of intrinsic haem, catabolism of [(14)C]methaemalbumin by microsomal haem oxygenase in vitro produced equimolar quantities of (14)CO and bilirubin, although these catabolites reflected only 18% of the degraded [(14)C]haem. This value was increased to 100% by addition of MnCl(2), which suggests that lipid peroxidation may be involved in degradation of exogenous haem to products other than CO. Phenyl-t-butylnitrone completely blocked haem oxygenase activity, which suggests that hydroxy free radicals may represent a species of active oxygen used by this enzyme system. After administration of carbon tetrachloride or 2-allyl-2-isopropylacetamide to labelled rats, hepatic [(14)C]haem was decreased and haem oxygenase activity was unchanged; however, (14)CO excretion was either unchanged (carbon tetrachloride) or decreased (2-allyl-2-isopropylacetamide). These changes were unaffected by cycloheximide pretreatment. From the lack of parallel losses of cytochrome P-450 [(14)C]haem and (14)CO excretion, one may infer that an important fraction of hepatic [(14)C]haem in normal rats is degraded by endogenous pathways not involving CO. We conclude that carbon tetrachloride and 2-allyl-2-isopropylacetamide accelerate catabolism of cytochrome P-450 haem through mechanisms that do not yield CO as an end product, and that are insensitive to cycloheximide and independent of haem oxygenase activity.
    [Abstract] [Full Text] [Related] [New Search]