Section 9
Chapter 8,713

Further characterization of two different reversible aldehyde oxidoreductases from Clostridium formicoaceticum, one containing tungsten and the other molybdenum

Huber, C.; Caldeira, J.; Jongejan, J.A.; Simon, H.

Archives of Microbiology 162(5): 303-309


ISSN/ISBN: 0302-8933
DOI: 10.1007/bf00263776
Accession: 008712979

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The tungsten- and the molybdenum-containing aldehyde oxidoreductases from Clostridium formicoaceticum show, for aldehydes, K-m values lt 30 mu-M and K-i values of millimolar concentrations. The tungsten-containing aldehyde oxidoreductase is inactivated to 50% by 3 mM KCN within 1 min, by 1 mM ferricyanide within 5 min, and by 0.05 mM chloralhydrate within 30 s. The molybdenum-containing AOR shows 50% inactivation within 1 min only with 70 mM KCN. The tungsten-containing enzyme is very sensitive to oxygen, especially in the reduced state, whereas the molybdenum-containing enzyme exhibits only moderate oxygen sensitivity without being markedly influenced by the redox state of the enzyme. The tungsten in the aldehyde oxidoreductase is bound to a pterin cofactor (Wco) of the mononucleotide form that is known for molybdopterin cofactor (Moco). The nature of the molybdenum cofactor in the molybdenum-containing aldehyde oxidoreductase is still unclear. The UV/VIS spectrum of the tungsten-containing aldehyde oxidoreductase shows a broad absorption in the range of 400 nm with a millimolar absorption coefficient of 18.1 (reduced form) and 24.8 (dehydrogenated form) at 396 nm. The epr spectrum exhibits two different W(V) signals with the following g values for signal A: 2.035, 1.959, 1.899 and signal B: 2.028, 2.017, 2.002. Dithionite-reduced enzyme shows signals of 4Fe-4S or 2Fe-2S clusters. Initial rate studies with different substrates for the carboxylate reduction led to a Bi Uni Uni Bi mechanism.

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