Fluorescent dye that is water-soluble and forms stable peptide bond with protein amino groups. Fluorescence emission of Fluorescent Dye 633-I Succinimidyl Ester is well separated from that of other commonly used red fluorophores, such as TAMRA, Texas Red, Alexa Fluor 594, Fluorescent Dye 594-I and R-phycoerythrin, making it ideal for multi-color labeling. In comparison with Alexa Fluor 633, the extinction coefficient of Fluorescent Dye 633-I Succinimidyl Ester is much higher (250,000 cm-1M-1).