Tetramethylrhodamine-5-iodoacetamide (5-TMRIA) is a thiol-selective reactive dye that is used to non-specifically label proteins via the cysteine residues. Tetramethylrhodamine-5-iodoacetamide (5-TMRIA) can be used to covalently label DNA fragments^[1]. In Vitro: Tetramethylrhodamine-5-iodoacetamide (0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 7.5 mM dye) shows different results for labeling carbonic anhydrase and myoglobin. At lower dye concentrations (up to 40:1 dye:thiol ratio) fluorescence labeling of only the carbonic anhydrase band is observed. However,as concentration increases, fluorescence labeling of both carbonic anhydrase and the lower myoglobin band is observed, indicating nonspecific labeling at these dye:thiol ratios^[1].