The mAb 3D9 reacts with a protein extracted from cow’s placenta. Results of an immunoblot are shown. Placenta-extracted proteins were separated in SDS-PAGE and blotted with the 3D9 mAb (Panel a) or a different control antibody as described in the text (Panel b). In Panel a, the arrow points to the band which was cut out from the membrane and used for the confirmation of native PAG1 in the immune complex using mass spectrometry. Lanes “M”, marker Precision Plus Protein Dual Color Standards (Biorad Cat. 1610394). The molecular masses of the marker bands are indicated.