Showa University School of Pharmacy 1 article published in JoVE Biochemistry Evaluation of Protein–Protein Interactions using an On-Membrane Digestion Technique Takashi Obama*1, Takuro Miyazaki*2, Toshihiro Aiuchi1, Akira Miyazaki2, Hiroyuki Itabe1 1Division of Biological Chemistry, Department of Molecular Biology, Showa University School of Pharmacy, 2Department of Biochemistry, Showa University School of Medicine Here, we present a protocol for an on-membrane digestion technique for the preparation of samples for mass spectrometry. This technique facilitates the convenient analysis of protein–protein interactions.