The beta-subunit of pea stem mitochondrial ATP synthase exhibits PPiase activity.
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.
Zancani
Marco
M
Sezione di Biologia Vegetale, Dipartimento di Biologia ed Economia Agro-Ind., Università di Udine, via Cotonificio 108, Udine 33100, Italy.
Casolo
Valentino
V
Peresson
Carlo
C
Federici
Giorgio
G
Urbani
Andrea
A
Macrì
Francesco
F
Vianello
Angelo
A