Figure 6. Biotin with a primary amine reacts with the MUC5AC C-terminus cleavage product.

Spent cell-culture medium from CHO-K1-pSM-MUC5AC-CH cells was immunoprecipitated with α-myc mAb-coated magnetic beads. Aliquots of the precipitated material were incubated for 1 h at 37 °C in a citric acid/Na₂HPO₄ (pH 7.2) buffer, a citric acid/Na₂HPO₄ (pH 5.4) buffer or in the buffers containing 1.5 μmol of B-EDA. After SDS/PAGE (7% gel; reducing conditions), the proteins were blotted and detected by either the α-myc mAb or streptavidin. Mono_ec, extracellular monomer of the MUC2 C terminus; M-C1_ec, N-terminal cleavage fragment. IB indicates the antibody used for detection. Positions of molecular-mass standards are indicated to the right.