ATP5B, also known as ATP Synthase H+ Transporting Mitochondrial F1 Complex Beta Polypeptide or simply ATP Synthase β5 subunit, is a crucial component of the mitochondrial ATP synthase enzyme complex. ATP5B serves as a catalytic core within the F1 complex of the ATP synthase, facilitating the synthesis of ATP from ADP and inorganic phosphate (Pi) using the electrochemical gradient across the mitochondrial inner membrane during oxidative phosphorylation.