This is one of the chains of the nonenzymatic component (CF(0) subunit) of the mitochondrial ATPase complex. ATP + 4 H(+)(in) + H2O = ADP + 5 H(+)(out) + phosphate F-type ATPases have 2 components, CF(1) - the catalytic core - and CF(0) - the membrane proton channel. CF(1) has five subunits: alpha(3), beta(3), gamma(1), delta(1), epsilon(1). CF(0) has three main subunits: a, b and c (By similarity). Belongs to the ATPase protein YMF19 family.