Biotin (Long Arm) NHS, 50 mg, is a N-hydroxysuccinimide (NHS) derivative of biotin with an aminohexanoate spacer arm to provide for maximum accessibility of biotin by avidin and streptavidin conjugates. The reagent will readily couple biotin under mild alkaline conditions to primary amino groups of proteins. Biotin (Long Arm) NHS is ideally suited to label antibodies, hormones, or other polypeptide molecules containing lysine residues. The linkage between biotin and proteins produced with this reagent is stable, with no significant loss of biotin on storage. 50 mg of Biotin (Long Arm) NHS is generally sufficient to label 500 mg of protein.