Mitochondrial ATP synthase is responsive to changes in cytosolic calci
um concentration, but the regulatory mechanisms are unclear. Here we i
dentified a major 52 kDa calcium-binding protein in rat enamel cells a
s the mitochondrial ATP synthase F-1-beta-subunit. The F-1-beta-subuni
t behaved as a low affinity and moderate capacity calcium-binding prot
ein during comparative Ca-45 overlay analyses, Equivalent behavior was
shown by the F-1-beta-subunit from rat liver mitochondria, but not by
the homologous F-1-alpha-subunit, supporting the specificity of calci
um binding. Evidence that the catalytic F-1-beta-subunit binds calcium
specifically introduces new mechanistic possibilities for regulating
ATP synthase, and thereby coordinating ATP production with demand for
ATP-fuelled calcium pump activity.