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Title: Studies on the mechanism of griseofulvin-induced protoporphyria.
Authors: Bellingham, Rachel Mary Ann.
Award date: 1994
Presented at: University of Leicester
Abstract: Griseofulvin induces protoporphyria in the mouse. The porphyria is caused by inhibition of ferrochelatase, the last enzyme of the liver haem biosynthetic pathway. Two N-alkylprotoporphyrins can be isolated from liver of griseofulvin-fed mice. One, N-methylprotoporphyrin, is a known ferrochelatase inhibitor. In this thesis NMR spectroscopy was used to determine the structure of the second adduct, N-GfPP, which is an N-monosubstituted protoporphyrin in which griseofulvin (minus a hydrogen atom) is attached to the NC pyrrole of protoporphyrin via an -N-CH2-O- linking group derived from either the 4- or 6-OCH3 group of the drug. A preliminary investigation into possible break-down products of N-GfPP is also described and suggestions made for the mechanism(s) of adduct formation. Individual regioisomers of N-alkylprotoporphyrins with varying N-alkyl groups were synthesised and separated. 1H and 13C NMR techniques were then used to identify structural differences between planar porphyrins and the synthetic N-alkylporphyrins. A discussion has been made of the effect of porphyrin ring currents on proton and carbon resonances. The purification of rat liver ferrochelatase is also described; however only small amounts of highly labile protein were obtained. Experiments devised to optimise the purification procedure also met with little success. Therefore, inhibition studies used cholate-solubilised ferrochelatase and synthetic N-alkylporphyrins. These studies confirm that the ferrochelatase inhibitory activity of an N-alkylporphyrin is dependent on the size and position of the N-alkyl substituent. The 1H NMR study of synthetic N-alkylporphyrins has also been linked to the inhibition analysis. This shows that the majority of N-alkylporphyrin enzyme inhibitors studied have equivalent 6 and 7 propionate groups, whereas the majority of N-alkylporphyrin non-inhibitors have distinctly non-equivalent 6 and 7 propionate groups. A proportion of the N-alkylporphyrins studied do not fit either description, but are still capable of inhibiting ferrochelatase. Mechanisms for the interaction of ferrochelatase with these compounds are therefore described.
Type: Thesis
Level: Doctoral
Qualification: Ph.D.
Rights: Copyright © the author. All rights reserved.
Appears in Collections:Theses, Dept. of Biochemistry
Leicester Theses

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