ATP5IF1 is an endogenous inhibitor of the F₁Fₒ-ATP synthase that prevents ATP depletion during bioenergetic stress 1. When mitochondrial membrane potential falls below a threshold and ATP synthase begins hydrolyzing ATP, ATP5IF1 blocks this wasteful reaction, thereby preserving cellular ATP pools 2. The protein also indirectly regulates heme synthesis in erythroid tissues by modulating mitochondrial pH and redox potential to enable efficient iron incorporation into protoporphyrin IX 1. Mechanistically, ATP5IF1 binds to phosphorylated ATP5F1A on the ATP synthase complex; when ATP5F1A is phosphorylated by TNK2/ACK1 kinase, it releases ATP5IF1, sustaining ATP synthase activity 3. ATP5IF1 deletion increases mitochondrial membrane hyperpolarization and triggers phospholipid remodeling that impacts nuclear DNA methylation and gene expression 4. Dysregulation of ATP5IF1 associates with multiple diseases. In acute myeloid leukemia, ATP5IF1 downregulation enables matrix ATP consumption that promotes chemotherapy resistance, while ATP5IF1 overexpression sensitizes cells to BCL-2 inhibitors 2. In idiopathic non-obstructive azoospermia, ATP5IF1 downregulation in Sertoli cells increases ATP hydrolysis and mitochondrial dysfunction 5. Elevated ATP5IF1 expression correlates with adverse cardiac outcomes in ischemic cardiomyopathy 6 and poor survival in CEBPA-mutant AML 7.