ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
O5. Different Reaction Mechanism of Beta-diketone Cleavage in Heme and
Non-heme Fe(II) Enzymes
S. Leitgeb, G. Straganz, B. Nidetzky
a Institute of Biotechnology and Biochemical Enginee, Graz University of Technology, Petersgasse 12/1, 8010,
Graz, Austria
e-mail: sleitgeb@tugraz.at
Diketone-cleaving enzyme (Dke1) of Acinetobacter johnsonii [1] is a non-heme iron (II) dependent dioxygenase
that belongs to the superfamily of the cupins [2]. The enzyme coordinates the active site metal by an unusual 3-
His motif that deviates from the general 2-His-1-carboxylate motif [3] which is widespread and has been
characterised extensively. We investigated the reaction mechanism of Dke1 in detail and proposed a reaction
mechanism for the degradation of beta-diketones [4, 5].
The heme-dependent enzyme horseradish peroxidase (HRP) has a very broad substrate spectrum and is also
capable of cleaving beta-diketones. HRP has already been reported to cleave 2, 4-pentanedione in the absence of
externally added hydrogen peroxide [6]. We made a detailed mechanistic investigation in order to elucidate the
reaction mechanism. Therefore we used a set of various diketones, characterized the reaction kinetically and
analyzed the product spectrum. We were able to distinguish between two mechanistic proposals be comparing
the distribution of two different product pairs. We could show deviations from the reaction route in Dke1 and
were able to present a different reaction mechanism for the degradation of beta-diketones in Dke1 and HRP.
References:
[1] Straganz, G.D. et al., Biochem. J., 369 (2003), 573-81.
[2] Khuri, S. et al., Mol. Biol. Evol., 18 (2001), 593-605.
[3] Hegg, E.L., and Que, L., Eur. J. Biochem., 250 (1997), 625-629.
[4] Straganz, G.D. et al., J. Am. Chem. Soc., 126 (2004), 12202-12203.
[5] Straganz, G.D. et al., J. Am. Chem. Soc., 127 (2005), 12306-12314.
[6] Rodrigues, A.P. et al., Biochim. Biophys. Acta, 1760 (2006), 1755-1761
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