Previously, we characterised the presence of ubiquitin and some ubiquitinated proteins (conjugates), which were considered as ubiquitin conjugates in the sarcoplasmic fraction of postmortem skeletal and cardiac muscles using SDS-PAGE and Western blot. In this study, an ubiquitin conjugate around 27 kDa was subjected to identification. The N-terminal amino acid sequence analysis generated by Edman degradation resulted in a 13 amino acid sequence (KIQFTVPLLEPHL), which is similar to that of Protein Phosphatase Inhibitor 1. Based on this result, Western blot analysis was performed by using a polyclonal antibody for Protein Phosphatase Inhibitor 1 and the conjugate was recognised and reacted clearly. Thus, the ubiquitinated protein around 27 kDa is identified as Protein Phosphatase Inhibitor 1. © 2009 Elsevier Ltd. All rights reserved.