The iron-sulfur centers of the pyruvate:ferredoxin oxidoreductase from Methanosarcina barkeri (Fusaro)

Abstract

The iron-sulfur clusters of a pyruvate:ferredoxin oxidoreductase isolated from a methanogenic archaeon, Methanosarcina barkeri (Fusaro), have been unambiguously identified for the first time. In agreement with the estimated iron and sulfur contents (Bock and Schönheit, Eur. J. Biochem., 237 (1996) 35–44), the enzyme is shown to contain three [4Fe-4S] 2+/1+ clusters, which in the reduced state give a complex EPR spectrum resulting from three distinct centres, magnetically interacting. The catalytic cycle of the enzyme was studied by visible and EPR spectroscopies. A thiamine diphosphate based radical is also an intermediate in the M. barkeri enzyme catalytic cycle. However, under anaerobic conditions, the enzyme or Clostridium pasteurianum ferredoxin iron-sulfur clusters are reduced only in the presence of both substrates, pyruvate and coenzyme A.