VCP and amyotrophic lateral sclerosis: One E3 that is especially important in muscle is Fbxo32/atrogin 1 (also named Mafbx), which may bind to p97,12 and adds ubiquitin molecules to the substrate, particularly during the accelerated degradation of muscle proteins that occurs during various types of atrophy, including that in cancer and most likely ALS.13, 14