Sulfo-NHS-LC-biotin (Sulfosuccinimidyl 6-(biotinamido) Hexanoate) is an amine-reactive biotinylation agent. As a water-soluble analog of NHS-LC-biotin, Sulfo-NHS-LC-biotin contains a negatively charged sulfonate group on the NHS ring structure, which creates sufficient polarity within the molecule and allows it to be directly added into aqueous reactions without prior dissolution of organic solvents. Sulfo-NHS-LC-biotin covalently binds to amine groups in proteins and other molecules through its NHS ester forming an amide linkage and releasing N-Hydroxysuccinimide. Sulfo-NHS-LC-biotin has a greater length (22.4 A) between a covalently modified molecule and the bicyclic biotin rings than NHS-biotin (13.5 A), which provides the probes a greater opportunity to reach the binding sites deeply buried inside the surface plane of proteins.

Reference

Bioconjugate Techniques , 2nd ed. By Greg T.Hermanson  (Pierce Biotechnology, Thermo Fisher Scientific, Rockford, IL).  Academic Press  (an imprint of Elsevier):  London, Amsterdam, Burlington, San Diego . 2008. ISBN 978-0-12-370501-3.

• Protein labeling—biotinylate antibodies to facilitate immobilization, purification or detection using streptavidin resins or probes
• Cell surface labeling—do not penetrate the plasma membrane, biotinylates only surface proteins of whole cells
• Amine-reactive—reacts with primary amines (-NH2), such as lysine side-chains, or the N-terminal-amine
• Soluble—charged sulfo-NHS group increases reagent water solubility compared to ordinary NHS-ester compounds
• Irreversible—forms permanent amide bonds; spacer arm cannot be cleaved
• Medium length—spacer arm is 22.4 angstroms; provides excellent balance between adequate length (minimal steric hindrance for biotin binding) and modest mass