Abstract: The F(1)c(10) sub-complex of the yeast F(1)F(0)-ATP synthase includes the membrane rotor part c(10)-ring linked to a catalytic head (alpha/beta)(3) by a central stalk (gammadeltaepsilon). The Saccharomyces cerevisiae yF(1)c(10):ADP sub-complex was crystallized in the presence of Mg.ADP, dicyclohexylcarbodiimide (DCCD) and azide. The structure was solved by molecular replacement using a high resolution model of the yeast F(1) and a bacterial c-ring model with 10 copies of the c-subunit. The structure refined to 3.43 A resolution displays new features compared to the original yF(1)c(10) and to the yF(1) inhibited by adenylyl-imidodiphosphate (AMP-PNP) (yF(1)(I-III)). An ADP molecule was bound in both beta(DP) and beta(TP) catalytic sites. The alpha(DP)-beta (DP) pair is slightly open and resembles the novel conformation identified in yF(1) whereas the alpha (TP)-beta(TP) pair is very closed and resembles more a DP pair. yF(1)c(10) provides a model of a new Mg.ADP-inhibited state of the yeast F(1). Like for the original yF(1) and yF(1)c(10):ADP structures, the foot of the central stalk is rotated by about 40 degrees with respect to bovine structures. The assembly of the F(1) central stalk with the F(0) c-ring rotor is mainly provided by electrostatic interactions. On the rotor ring, the essential cGlu(59) carboxylate group is surrounded by hydrophobic residues and is not involved in hydrogen bonding.