title: The beta-subunit of pea stem mitochondrial ATP synthase exhibits PPiase activity.
abstract: A soluble protein with a molecular mass of 55 kDa has been purified from etiolated pea stem mitochondria. The protein exhibits a Mg2+-requiring PPiase activity, with an optimum at pH 9.0, which is not stimulated by monovalent cations, but inhibited by F-, Ca2+, aminomethylenediphosphate and imidodiphosphate. The protein does not cross-react with polyclonal antibodies raised against vacuolar, mitochondrial or soluble PPiases, respectively. Conversely, it cross-reacts with an antibody for the alpha/beta-subunit of the ATP synthase from beef heart mitochondria. The purified protein has been analyzed by MALDI-TOF mass spectrometry and the results, covering the 30% of assigned sequence, indicate that it corresponds to the beta-subunit of the ATP synthase of pea mitochondria. It is suggested that this enzymatic protein may perform a dual function as soluble PPiase or as subunit of the more complex ATP synthase.
authors.affiliation: Sezione di Biologia Vegetale, Dipartimento di Biologia ed Economia Agro-Ind., Università di Udine, via Cotonificio 108, Udine 33100, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Zancani
authors.forename: Valentino
authors.initials: V
authors.lastname: Casolo
authors.forename: Carlo
authors.initials: C
authors.lastname: Peresson
authors.forename: Giorgio
authors.initials: G
authors.lastname: Federici
authors.forename: Andrea
authors.initials: A
authors.lastname: Urbani
authors.forename: Francesco
authors.initials: F
authors.lastname: Macrì
authors.forename: Angelo
authors.initials: A
authors.lastname: Vianello