However, immunoblotting for protein subunits of respiratory complexes showed that the level of Mitochondrial complex V protein ATP5A (complex V ATP synthase) was significantly lower in the sensitive MLL-r leukemia cells (Fig. 5h) while levels of respiratory complex II and IV proteins (SDHB and COX2, respectively) did not differ between sensitive and unresponsive cells (Supplementary Figure 5a). Here, SDHB is linked to leukemia.