1. ^{{cite journal | vauthors = Polgár L | title = Isolation of highly active papaya peptidases A and B from commercial chymopapain | journal = Biochimica et Biophysica Acta | volume = 658 | issue = 2 | pages = 262–9 | date = April 1981 | pmid = 7018581 | doi = 10.1016/0005-2744(81)90296-5 }}
2. ^{{cite journal | vauthors = Buttle DJ, Kembhavi AA, Sharp SL, Shute RE, Rich DH, Barrett AJ | title = Affinity purification of the novel cysteine proteinase papaya proteinase IV, and papain from papaya latex | journal = The Biochemical Journal | volume = 261 | issue = 2 | pages = 469–76 | date = July 1989 | pmid = 2505761 | pmc = 1138849 }}
3. ^{{cite journal | vauthors = Ritonja A, Buttle DJ, Rawlings ND, Turk V, Barrett AJ | title = Papaya proteinase IV amino acid sequence | journal = FEBS Letters | volume = 258 | issue = 1 | pages = 109–12 | date = November 1989 | pmid = 2591528 | doi = 10.1016/0014-5793(89)81627-8 }}
4. ^{{cite journal | vauthors = Buttle DJ, Ritonja A, Pearl LH, Turk V, Barrett AJ | title = Selective cleavage of glycyl bonds by papaya proteinase IV | journal = FEBS Letters | volume = 260 | issue = 2 | pages = 195–7 | date = January 1990 | pmid = 2404797 | doi = 10.1016/0014-5793(90)80101-n }}
5. ^{{cite journal | vauthors = Buttle DJ, Ritonja A, Dando PM, Abrahamson M, Shaw EN, Wikstrom P, Turk V, Barrett AJ | title = Interactions of papaya proteinase IV with inhibitors | journal = FEBS Letters | volume = 262 | issue = 1 | pages = 58–60 | date = March 1990 | pmid = 1690669 | doi = 10.1016/0014-5793(90)80153-a }}