Biotin-PEG3-Mal is a PEG derivative containing a biotin group and a maleimide group for labeling and crosslinking cysteines and other sulfhydryls. The maleimide group reacts specifically with sulfhydryl groups (at pH 6.5-7.5) to form a stable, irreversible thioether linkage. The hydrophilic PEG spacer increases solubility in aqueous media of the molecules conjugated to the biotin compound. It also helps to minimize steric hindrance involved with the binding to avidin molecules.
