Direct FeS cluster involvement in generation of a radical in lysine 2,3-aminomutase

Lysine 2,3-aminomutase (KAM) belongs to a class of enzymes that use FeS clu sters and S-adenosyl-L-methionine to initiate radical-dependent chemistry. Selenium K-edge X-ray absorption spectroscopic analysis of KAM poised at va rious stages of catalysis, in the presence of selenomethionine or Se-adenos yl-L-selenomethionine, reveals that the cofactor is cleaved only in the pre sence of dithionite and the substrate analogue trans-4,5-dehydrolysine. A n ew Fourier transform peak at 2.7 Angstrom, assigned as a Se-Fe interaction, appears concomitant with this cleavage. This is the first demonstration of a direct interaction of S-adenosyl-L-methionine, or its cleavage products, with the FeS cluster in this class of enzymes.