Biotin synthase, a member of the ‘radical SAM’ (S-adenosylmethionine) family, converts DTB (dethiobiotin) into biotin. The active form of the Escherichia coli enzyme contains two (Fe-S) centres, a (4Fe-4S) and a (2Fe-2S). The (4Fe-4S)2+/+ mediates the electron transfer required for the reductive cleavage of SAM into methionine and a DOA• (deoxyadenosyl radical). Two DOA•, i.e. two SAM molecules, are consumed to activate the positions 6 and 9 of DTB. A direct transfer of isotope from the labelled substrate into DOAH (deoxyadenosine) has been observed with 2H, although not quantitatively, but not with tritium. The source of the sulphur introduced to form biotin is still under debate. We have shown that the (2Fe-2S)2+ cluster can be reconstituted in the apoenzyme with S2− and Fe2+. When S2− was replaced by [34S2−], [35S2−] or Se2−, biotin containing mostly the sulphur isotopes or selenium was obtained. This leads us to favour the hypothesis that the (2Fe-2S) centre is the sulphur donor, which may explain the absence of turnover of the enzyme. DTBSH (9-mercaptodethiobiotin), which already contains the sulphur atom of biotin, was shown to be an alternative substrate of biotin synthase both in vivo and with a crude extract. When this compound was tested with a well-defined in vitro system, the same turnover of one and similar reaction rates were observed for DTB and DTBSH. We postulate that the same intermediate is formed from both substrates.
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Conference Article|
August 01 2005
Biotin synthase mechanism: an overview
M. Lotierzo;
M. Lotierzo
1Synthèse, Structure et Fonction de Molécules Bioactives, UMR CNRS 7613, Université Paris VI, 4 place Jussieu, 75252 Paris Cedex 05, France
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B. Tse Sum Bui;
B. Tse Sum Bui
1Synthèse, Structure et Fonction de Molécules Bioactives, UMR CNRS 7613, Université Paris VI, 4 place Jussieu, 75252 Paris Cedex 05, France
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D. Florentin;
D. Florentin
1Synthèse, Structure et Fonction de Molécules Bioactives, UMR CNRS 7613, Université Paris VI, 4 place Jussieu, 75252 Paris Cedex 05, France
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F. Escalettes;
F. Escalettes
1Synthèse, Structure et Fonction de Molécules Bioactives, UMR CNRS 7613, Université Paris VI, 4 place Jussieu, 75252 Paris Cedex 05, France
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A. Marquet
A. Marquet
1
1Synthèse, Structure et Fonction de Molécules Bioactives, UMR CNRS 7613, Université Paris VI, 4 place Jussieu, 75252 Paris Cedex 05, France
1To whom correspondence should be addressed (email marquet@ccr.jussieu.fr).
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Publisher: Portland Press Ltd
Received:
April 22 2005
Online ISSN: 1470-8752
Print ISSN: 0300-5127
© 2005 The Biochemical Society
2005
Biochem Soc Trans (2005) 33 (4): 820–823.
Article history
Received:
April 22 2005
Citation
M. Lotierzo, B. Tse Sum Bui, D. Florentin, F. Escalettes, A. Marquet; Biotin synthase mechanism: an overview. Biochem Soc Trans 1 August 2005; 33 (4): 820–823. doi: https://doi.org/10.1042/BST0330820
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