DnrK colorimetric assay. (A) General scheme for a high-throughput DnrK colorimetric assay enabled by the surrogate acceptor 2-chloro-4-nitrophenol (ClNP). (B) Representative assay results demonstrating DnrK-catalyzed alkylation of ClNP diminishes classical ClNP color (A410) over time [30 μM DnrK; 500 μM ClNP; AdoMet: (i) 100 μM, (ii) 500 μM, (iii) 800 μM, (iv) 1,000 μM, (v) 1,600 μM, and (vi) 2,000 μM; 25 mM Tris· HCl; pH 8.0].