CysG, also known as uroporphyrinogen III methylase and sirohaem synthase (CysG; EC 2.1.1.107), is a multifunctional enzyme that is able to transform uroporphyrinogen III into sirohaem via two S-adenosyl-L-methionine (AdoMet)-dependent transmethylations, an NAD+-dependent dehydrogenation and a ferrochelation. The apparent tight binding of AdoMet to this multifunctional enzyme is investigated. The use of a rapid AdoMet binding assay demonstrates that CysG becomes labelled with both [methyl-3H]AdoMet and [carboxyl-14C]AdoMet. Further experiments show that the CysG-AdoMet complex is subsequently able to methylate uroporphyrinogen III. CysG remains associated with the labelled constituents of the AdoMet even after denaturation with urea and SDS/PAGE, suggesting that the AdoMet has become covalently linked to the protein. A rapid examination of some of the other transmethylases involved in corrin biosynthesis reveals that they bind the AdoMet in a similar fashion. A multistep transmethylation mechanism is proposed to explain the observed results.
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January 1996
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Research Article|
January 15 1996
Evidence for a covalent intermediate in the S-adenosyl-l-methionine-dependent transmethylation reaction catalysed by sirohaem synthase Available to Purchase
Sarah C. WOODCOCK;
Sarah C. WOODCOCK
1Department of Molecular Genetics, Institute of Ophthalmology, Bath Street, London EC1V 9EL, U.K.
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Martin J. WARREN
Martin J. WARREN
*
*To whom correspondence should be addressed.
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Publisher: Portland Press Ltd
Received:
June 19 1995
Revision Received:
August 14 1995
Accepted:
August 25 1995
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1996
1996
Biochem J (1996) 313 (2): 415–421.
Article history
Received:
June 19 1995
Revision Received:
August 14 1995
Accepted:
August 25 1995
Citation
Sarah C. WOODCOCK, Martin J. WARREN; Evidence for a covalent intermediate in the S-adenosyl-l-methionine-dependent transmethylation reaction catalysed by sirohaem synthase. Biochem J 15 January 1996; 313 (2): 415–421. doi: https://doi.org/10.1042/bj3130415
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