Radical S-Adenosylmethionine Enzymes

ing a H-atom from substrate. These and other kinetics studies demonstrated that PFL-AE could undergo multiple turnover events, with the 150 PFL activations per PFL-AE reported in Table 1 not the upper limit, but rather a number limited by the PFL:PFL-AE ratio in the steady-state kinetics assays. As can be seen from the data summarized in Table 1, PFL-AE is one of the few radical SAM enzymes demonstrated to be truly catalytic. Many of the enzymes studied to date undergo very few turnover events in vitro, reflecting both the difficulties in preparing and assaying active radical SAM enzymes and the challenging issues related to product stability/quantitation. 3.1.3. Defining the Unique SAM−Cluster Interaction in Radical SAM Enzymes. The CX3CX2C motif in PFL-AE, Table 2. continued enzyme organism λmax (nm) a sample type EPR (g-values) [4Fe−4S] cluster Mössbauer parameters (mm/s) ref Radical SAM Enzymes Coordinating Auxiliary Fe−S Clusters reduced, 2.04, 1.92 reduced + SAM, 1.99, 1.83 reduced + SAM + substrate,, 2.05, 1.96, 1.87 AtsB Klebsiella pneumoniae 395,,, as-isolated N.R. [4Fe−4S]: ∂ = 0.44; ΔEQ = 1.17 (94%), 79, 80b RimO Escherichia coli 410,, as-isolated, 2.01 [4Fe−4S]: ∂ = 0.43, ΔEQ = 1.07 (90%), 138 as-isolated + SAM, [4Fe−4S]: (∂1 = 0.43, ΔEQ1 = 1.07 (58%); ∂2 = 0.70, ΔEQ2 = 1.24 (16%); ∂3 = 0.37, ΔEQ3 = 0.81 (16%)), as-isolated, [4Fe−4S]: ∂ = 0.43, ΔEQ = 1.12 (62%), as-isolated + SAM, [4Fe−4S]: (∂1 = 0.43, ΔEQ1 = 1.12 (44%); ∂2 = 0.70, ΔEQ2 = 1.24 (9%); ∂3 = 0.37, ΔEQ3 = 0.81 (9%)), reduced, 2.06, 1.98, 1.94