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 asaccha rolyticus, 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 ch aracteristic of a [3Fe-4S](+) cluster constituting 1% of the total enz yme concentration. Upon incubation of the enzyme under air the intensi ty of the [3Fe-4S](+) signal increased correlating with the loss of en zymatic activity. Addition of L-serine prevented this. Hence, active L -serine dehydratase probably contains a diamagnetic [4Fe-4S](2+) clust er which is converted by oxidation and loss of one iron ion to a param agnetic [3Fe-4S](+) cluster, resulting in inactivation of the enzyme. In analogy to the mechanism elucidated for aconitase, it is proposed t hat L-serine is coordinated via its hydroxyl and carboxyl groups to th e labile iron atom of the [4Fe4S](2+) cluster.