X-press Tag is an N-terminal leader peptide; this N-terminal peptide contains a polyhistidine sequence, the Xpress epitope (part of bacteriophage T7 gene 10 protein) and an enterokinase cleavage site. Anti-Xpress antibodies recognize the Xpress epitope sequence found in this leader peptide.

D-Ala-D-Ala constitutes the terminus of the peptide part of the peptidoglycan monomer unit and is involved in the transpeptidation reaction as the substrate. D-Ala-D-Ala is catalyzed by D-Alanine-D-Alanine ligase. D-Ala-D-Ala is a bacterial endogenous metabolite.

2-Bromobiphenyl is a chemical compound.