Olsen C, Wagtmann N (2003). "Identification and characterization of human DPP9, a novel homologue of dipeptidyl peptidase IV". Gene. 299 (1–2): 185–93. doi:10.1016/S0378-1119(02)01059-4. PMID12459266.
Ajami K, Abbott CA, Obradovic M, et al. (2003). "Structural requirements for catalysis, expression, and dimerization in the CD26/DPIV gene family". Biochemistry. 42 (3): 694–701. doi:10.1021/bi026846s. PMID12534281.
Ogasawara W, Tanaka C, Suzuki M, et al. (2005). "Isoforms of dipeptidyl aminopeptidase IV from Pseudomonas sp. WO24: role of the signal sequence and overexpression in Escherichia coli". Protein Expr. Purif. 41 (2): 241–51. doi:10.1016/j.pep.2004.10.027. PMID15866709.
Yu DM, Wang XM, Ajami K, et al. (2006). "DP8 and DP9 have extra-enzymatic roles in cell adhesion, migration and apoptosis". Adv. Exp. Med. Biol. Advances in Experimental Medicine and Biology. 575: 63–72. doi:10.1007/0-387-32824-6_7. ISBN978-0-387-29058-4. PMID16700509.