The DYKDDDDK peptide is one of the most commonly used tags in fusion protein expression and purification. The DYKDDDDK peptide is also often referred to as the Flag® peptide, which is a registered trademark of Sigma. It can be fused to the N-terminus, C-terminus, or within the sequence of a fusion protein. Highly hydrophilic, it is more readily displayed on the surface of the fusion protein, minimizing the likelihood of interfering with the protein’s function. This tag offers an additional advantage: when fused to the N-terminus of the target protein, it can be cleaved by Enterokinase (EK protease) at the C-terminal side of its aspartic acid residue, leaving no residual amino acids. Antibodies against the DYKDDDDK tag enable precise detection and purification of DYKDDDDK-tagged fusion proteins. By conjugating Horseradish Peroxidase (HRP) to the anti-DYKDDDDK antibody through a specific process, the tagged fusion protein can be rapidly detected in Western blot (WB) assays. Upon adding chemiluminescent substrates A and B (typically luminol and hydrogen peroxide), catalyzed by HRP, luminol reacts with hydrogen peroxide to form an unstable peroxide intermediate. This intermediate decomposes, generating an electronically excited state species. When this species returns to the ground state, light is emitted, enabling rapid detection of the DYKDDDDK-tagged fusion protein.