Mössbauer study of the native, reduced and substrate-reacted <em>Desulfovibrio gigas</em> aldehyde oxido-reductase.

The Desulfovibrio gigas aldehyde oxido-reductase contains molybdenum and iron-sulfur clusters. M&#246;ssbauer spectroscopy was used to characterize the iron-sulfur clusters. Spectra of the enzyme in its oxidized, partially reduced and benzaldehyde-reacted states were recorded at different temperatures and applied magnetic fields. All the iron atoms in D. gigas aldehyde oxido-reductase are organized as [2Fe-2S] clusters. In the oxydized enzyme, the clusters are diamagnetic and exhibit a single quadrupole doublet with parameters (ΔEQ = 0.62 &#177; 0.02 mm/s and δ = 0.27 &#177; 0.01 mm/s) typical for the [2Fe-2S]2+ state. M&#246;ssbauer spectra of the reduced clusters also show the characteristics of a [2Fe-2S]1+ cluster and can be explained by a spin-coupling model proposed for the [2Fe-2S] cluster where a high-spin ferrous ion (S = 2) is antiferromagnetically coupled to a high-spin ferric ion (S = 5/2) to form a S = &#189; system. Two ferrous sites with different ΔEQ values (3.42 mm/s and 2.93 mm/ s at 85 K) are observed for the reduced enzyme, indicating the presence of two types of [2Fe-2S] clusters in the D. gigas enzyme. Taking this observation together with the re-evaluated value of iron content (3.5 &#177; 0.1 Fe/molecule), it is concluded that, similar to other Mo-hydroxylases, the D. gigas aldehyde oxido-reductase also contains two spectroscopically distinguishable [2Fe-2S] clusters. [ABSTRACT FROM AUTHOR]