(A, B) Western blots were prepared using mouse brain homogenate (Brain; 100 μg) or HEK293 cell extracts (1% of 10 -cm plate), either transfected to express FLAG-MPP2 (HEK) or empty plasmid (HEK mock). Duplicate lanes were prepared and one set was probed with the indicated MPP2 antibody (left panels) while the second set was probed with the same antibody after pre-absorbing with the immunizing antigen (right panels). Native MPP2 and transfected FLAG-MPP2 were detected only in the left panels. (C) Bar graphs illustrating abundance ratios determined for the indicated proteins in APs with two anti-MPP2 antibodies and IgG as a negative control. Horizontal lines denote threshold for specificity of co-purification. (D) Western blots of proteins prepared from HEK293 cells transfected with C8-tagged SAP97, Lin7A, Lin7C, and MPP2, and probed with anti-C8 antibody (left), anti-MPP2a antibody (middle), and anti-MPP2b antibody (right). The MPP2 antibodies recognized only MPP2.