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Human Sco1 and Sco2 are copper-binding proteins involved in the assembly of mitochondrial cytochrome c oxidase. As proper assembly of cytochrome c oxidase is essential for the production of ATP, mutations in Sco1/2 have been shown to cause distinct and fatal myopathies in humans. Recently, we determined the crystal structure of the conserved, intermembrane portion of hSCO1 (Williams et al (2005) J. Biol. Chem. 280, 15202-11). Its similarity to redox-active proteins, including thioredoxins (Trx) and peroxiredoxins (Prx), suggest that Sco may have catalytic activity. Likewise, its similarity to PrrC, a Sco homolog in R. sphaeroides known to be involved in regulating the transcription of photosynthetic gene products, suggest that Sco1/2 are involved in redox signaling. Recent efforts in other labs suggest that p53 regulates Sco2 transcription and switches the cell’s respiration to glycolysis, prompting a direct linkage to the Warburg effect (Hwang and colleagues at the NIH, Science (2006) 312, pp. 1650-3)