Schematic representation of the pioglitazone (PGZ)-induced fragmentation of complex I (A) into four subcomplexes. In the presence of PGZ, the membranous arm of complex I releases a fragment of 250 kDa (E). As a result of this release, one subcomplex of about 600 kDa (B) is formed. Subsequently, the membrane arm of subcomplex (B) releases a second fragment of 350 kDa (D). Thereafter, the remaining complex I is limited to a subcomplex of 400 kDa (C). Subcomplexes (B) and (C) contain the NADH:dehydrogenase module and consequently have in-gel dehydrogenase activity.