1. Institute of Protein Biochemistry, CNR, Via Marconi 12, I-80125 Napoli, Italy, Department of Biochemistry and Biophysics, II University of Napoli, Via Costantinopoli 16, I-80138 Napoli, Italy, and Department of Plant Biology, University of Roma “La Sapienza”, Piazzale Aldo Moro 5, I-00185 Roma, Italy