The Borenpharm Mal-(PEG)n-NHS Ester is water-soluble heterobifunctional crosslinkers that contain N-hydroxysuccinimide (NHS) ester and maleimide groups that allow covalent conjugation of amine- and sulfhydryl-containing molecules. NHS esters react with primary amines at pH 7-9 to form amide bonds, while maleimides react with sulfhydryl groups at pH 6.5-7.5 to form stable thioether bonds. In aqueous solutions, NHS ester hydrolytic degradation is a competing reaction whose rate increases with pH. The maleimide group is more stable than the NHS-ester group but will slowly hydrolyze and loses its reaction specificity for sulfhydryls at pH values > 7.5. For these reasons, conjugations with these crosslinkers are usually performed at pH 7.2-7.5, with the NHS-ester (amine-targeted) reacted before or simultaneous with the maleimide (sulfhydryl-targeted) reaction.
Mal-(PEG)n-NHS Esters are often used to prepare antibody-enzyme and hapten-carrier protein conjugates in a two-step reaction scheme. First, the amine-containing protein is reacted with a several-fold molar excess of the crosslinker, followed by removal of excess (nonreacted) reagent by desalting or dialysis; finally, the sulfhydryl-containing molecule is added to react with the maleimide groups already attached to the first protein.
Mal-(PEG)n-NHS Ester is soluble in water and many other aqueous buffers to approximately 10mM, although solubility decreases with increasing salt concentration. Mal-(PEG)n-NHS Ester is not directly water-soluble and must be dissolved in an organic solvent such as dimethylsulfoxide (DMSO) or dimethylformamide (DMF); subsequent dilution into aqueous reaction buffer is generally possible, and most protein reactants will remain soluble if the final concentration of organic solvent is less than 10%.
Important Product Information
Mal-(PEG)n-NHS esters are moisture-sensitive. Store reagent vial in desiccant. Equilibrate vial to room temperature before opening to avoid moisture condensation inside the container. Dissolve needed amount of reagent and use it immediately before hydrolysis occurs. Discard any unused reconstituted reagent. Do not store reagent in solution.