IRON-SULFUR CLUSTER-CONTAINING L-SERINE DEHYDRATASE FROM PEPTOSTREPTOCOCCUS-ASACCHAROLYTICUS - CORRELATION OF THE CLUSTER TYPE WITH ENZYMATIC-ACTIVITY

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 [4Fe4S](2+) cluster.