The iron–sulfur cluster in the l ‐serine dehydratase TdcG from Escherichia coli is required for enzyme activity

The anaerobically inducible l ‐serine dehydratase, TdcG, from Escherichia coli was characterized. Based on UV–visible spectroscopy, iron and labile sulfide analyses, the homodimeric enzyme is proposed to have two oxygen‐labile [4Fe–4S] 2+ clusters. Anaerobically isolated dimeric TdcG had a k cat of 544 s −1 and an apparent K M for l ‐serine of 4.8 mM. l ‐threonine did not act as a substrate for the enzyme. Exposure of the active enzyme to air resulted in disappearance of the broad absorption band at 400–420 nm, indicating a loss of the [4Fe–4S] 2+ cluster. A concomitant loss of dehydratase activity was demonstrated, indicating that integrity of the [4Fe–4S] 2+ cluster is essential for enzyme activity.