DMAC1 (distal membrane arm assembly component 1) is a mitochondrial inner membrane protein essential for assembling the distal region of complex I (NADH:ubiquinone oxidoreductase), the first enzyme of the mitochondrial respiratory chain 1. Complex I comprises 45 human subunits, and DMAC1 is among the 25 accessory subunits strictly required for assembly of a functional complex 1. Proteomic analysis demonstrates that DMAC1 loss specifically impairs assembly of the distal membrane arm portion of complex I 1. DMAC1 is an N-myristoylated protein localized to mitochondria, with two conserved cysteines in a Cx2C motif that are structurally important 2. The yeast homologue Dmo2p is required for stability and maturation of Cox2p, the cytochrome c oxidase subunit harboring the copper-binding CuA center, suggesting DMAC1 may support metal incorporation during respiratory complex assembly 3. Beyond its canonical role in complex I assembly, DMAC1 shows genetic association with lean body mass, particularly in females, with high expression in skeletal muscle 4. Complex I dysfunction, in which DMAC1 participates, is implicated in mitochondrial disease, Parkinson's disease, and aging 1.