Purification and characterization of the X-prolyl-dipeptidyl aminopeptidase (PepX) from Streptococcus macedonicus and cloning of the pepX gene Marina D. Georgalaki, Marina Papdelli, Rania Anastasiou, George Kalantzopoulos and Effie Tsakalidou Lait, 82 6 (2002) 657-671 DOI: 10.1051/lait:2002040