Bacterial L-serine dehydratases: a new family of enzymes containing iron-sulfur clusters.

Two families of enzymes are described which catalyse identical chemical reactions but differ in their prosthetic groups and hence in their mechanism of action. One family, the pyridoxal-5'-phosphate (PLP)-dependent L-threonine dehydratases, also use L-serine as substrate. The other, hitherto unrecognized family is the iron-dependent, highly specific bacterial L-serine dehydratases. It has been shown that L-serine dehydratase from the anaerobic bacterium Peptostreptococcus asaccharolyticus contains an iron-sulfur cluster but no PLP. A mechanism for the dehydration of L-serine which is similar, but not identical, to that of the dehydration of citrate catalysed by aconitase is proposed.