Chloroplast atpase in acetabularia acetabulum: Purification and characterization of chloroplast f₁-ATPase

AT Pases were isolated from chloroplasts of the unicellular marine alga Acetabularia acetabulum. Two preparations of ATPase, a chloroplast-enriched fraction and an αβγ-complex were compared. The αβγ-complex was released into an EDTA solution and purified by anion-exchange chromatography, hydrophobic chromatography, and gel permeation chromatography. The subunit composition of this enzyme appeared to be 52-53 (α), 51(β), and 40(γ)kDa from SDS–PAGE. ATPase activity was enriched about 260-fold to a specific activity of approximate 4.1 U · mg protein ⁻¹. The catalytic properties of the αβγ-complex were as follows: pH optimum at 7.5; substrate specificity, ATP > ITP, GTP > UTP = CTP (K_m for ATP 0.2 mM); divalent cation requirement, Mg^{2 +} = Mn^{2 +} = Co^{2 +} > Zn^{2 +} > Ni^{2 +} > Ca^{2 +}; ATPase activity was inhibited by monovalent anions, while monovalent cations had neither inhibitory nor stimulatory effects. Orthovanadate had no inhibitory effect on the enzyme activity of αβγ-complex. Azide was the most effective inhibitor of the αβγ-complex. N-Terminal amino acid sequences of the α and β subunits were not obtained and appeared to be blocked. The γ subunit gave a sequence of AGLKEMKD-XIGSVXNTKKI, which showed 60% similarity to the γ subunits of spinach and Chlamydomonas reinhardtii CF₁-ATPase and EF₁-ATPase.