Résumé
The isolation and partial characterization of the oligomycin-sensitive F
0F
1-ATP synthase/ATPase from the colorless alga
Polytomella spp. is described. Purification was performed by solubilization with dodecyl-
β-
d-maltoside followed by Sepharose Hexyl ammonium chromatography, a matrix that interacts with the F
1 sector of mitochondrial ATPases. The
α-subunit, which migrates on SDS-polyacrylamide gels with an apparent molecular mass of 55 kDa, was identified by the N-terminal sequencing of 47 residues. This subunit exhibited a short extension at its N-terminus highly similar to the one described for the unicellular alga
Chlamydomonas reinhardtii (Nurani, G. and Franzén L.-G. (1996) Plant Mol. Biol. 31, 1105–1116). In whole mitochondria, the
α-subunit was susceptible to limited proteolytic digestion induced by heat. An endogenous protease removed the first 22 residues of the mature
α-subunit. Subunit
β was also identified by N-terminal sequencing of 31 residues. This subunit of 63 kDa exhibited a higher apparent molecular mass than
α, as judged by its mobility on denaturing polyacrylamide gel electrophoresis. This
β-subunit is 7–8 kDa larger than the
β-subunits of other mitochondrial ATPases. It is suggested that the
β-subunit from
Polytomella spp. may have a C-terminal extension similar to that described for the green alga
C.
reinhardtii (Franzén, L.-G. and Falk, G. (1992) Plant Mol. Biol. 19, 771–780). In addition, it was found that the C-terminal extension of the
β-subunit of
C.
reinhardtii showed homology with the endogenous ATPase inhibitors from various sources and with the
ϵ-subunit from the F
0F
1-ATP synthase from
Escherichia coli, which is considered to be a functional homolog of the inhibitor proteins. The data reported here provide the first biochemical evidence for a close relationship between the colorless alga
Polytomella spp. and its photosynthetic counterpart
C.
reinhardtii. It is also suggested that the C-terminal extensions of the
β-subunits of the ATP synthases from these algae, may play a regulatory role in these enzymes.