NirJ, a radical SAM family member of the d1 heme biogenesis cluster.

NirJ is involved in the transformation of precorrin-2 into heme d(1), although its precise role in the process has not been established. The purified protein was found to contain a 4Fe-4S centre, in line with the prediction that it belongs to the radical SAM class of enzymes. This was further confirmed by binding of S-adenosyl-L-methionine (SAM) to dithionite-reduced NirJ, which resulted in a decrease in the signal intensity and in a shift to higher field of the [4Fe-4S](1+) EPR signal. Significantly, though, this approach also led to the appearance of a small but reproducible organic radical signal that was associated with about 2% of the NirJ molecules and was affected by the incorporation of SAM deuterated at the 5' adenosyl group. Copyright 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.