Produces ATP from ADP in the presence of a proton gradient across the membrane. The catalytic sites are hosted primarily by the beta subunits (By similarity). 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 four main subunits: a(1), b(1), b'(1) and c(9-12) (By similarity). The 56 kDa isoform is not detected in etiolated cotyledons The 54 kDa isoform exists even in the dark and increases very rapidly for 96 hours upon illumination. The 56 kDa isoform is constitutively expressed. The 54 kDa isoform increases 9-fold during 10 hours of high light stress and decreases after 24 hours of photoinhibitory treatment. The N-terminus is blocked. Two isoforms of 54 and 56 kDa with the same peptide fingerprint are found in the chloroplast. The synthesis of the major 56 kDa isoform is coupled to the assembly into the thylakoid membrane, while the 54 kDa isoform accumulates in response to various light stress conditions. Belongs to the ATPase alpha/beta chains family.