Coimmunoprecipitation of wt PLN with L67 mutants of SERCA1a. Microsomal fractions from HEK-293 cells coexpressing wt PLN and SERCA1a L67 mutants were dissolved in Tween 20, specific proteins were coimmunoprecipitated with anti-PLN antibody IDII, and the precipitate was separated by 8% SDS/PAGE. After electrophoresis, the proteins were transferred to a nitrocellulose membrane and stained with anti-SERCA1a antibody, A52. The Upper row was stained with the A52 antibody against SERCA1 and defines the relative amount of SERCA1a that was coimmunoprecipitated with antibody ID11 against PLN. The Lower row shows staining of 10 μg of microsomes from each expressed sample with the A52 antibody, to show that each mutant SERCA1 was well expressed.