Iron—sulfur cluster‐containing l‐serine dehydratase from Peptostreptococcus asaccharolyticus: Correlation of the cluster type with enzymatic activity

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Abstract
Investigations were performed with regard to the function of the iron—sulfur cluster of l‐serine dehydratase from Peptostreptococcus asaccharolyticus, an enzyme which is novel in the class of deaminating hydro‐lyases in that it lacks pyridoxal‐5′‐phosphate. Anaerobically purified l‐serine dehydratase from P. asaccharolyticus revealed EPR spectra characteristic of a [3Fe–4S]+ cluster constituting 1% of the total enzyme concentration. Upon incubation of the enzyme under air the intensity of the [3Fe–4S]+ signal increased correlating with the loss of enzymatic activity. Addition of l‐serine prevented this. Hence, active l‐serine dehydratase probably contains a diamagnetic [4Fe–4S]2+ cluster which is converted by oxidation and loss of one iron ion to a paramagnetic [3Fe–4S]+ cluster, resulting in inactivation of the enzyme. In analogy to the mechanism elucidated for aconitase, it is proposed that l‐serine is coordinated via its hydroxyl and carboxyl groups to the labile iron atom of the [4Fe–4S]2+ cluster.