Tetramethylrhodamine-5-iodoacetamide (5-TMRIA) is a thiol-selective reactive dye used to non-specifically label proteins through cysteine residues and to covalently label DNA fragments [1].

Tetramethylrhodamine-5-iodoacetamide, at concentrations ranging from 0.5 to 7.5 mM, demonstrates varying effects on the fluorescence labeling of carbonic anhydrase and myoglobin. Initial observations reveal exclusive labeling of the carbonic anhydrase band at low dye concentrations (up to a 40:1 dye:thiol ratio). With increased concentrations, however, both carbonic anhydrase and the less prominent myoglobin band exhibit fluorescence labeling, indicating nonspecific interactions at these dye:thiol ratios[1].