A new peptide (1341 g/mol) from Jatropha curcas seeds was isolated. The linear sequence (APTLSG-GSVPRDAD) was deduced by de novo peptide sequencing, and further used as scaffold for synthesis of linear (1342 g/mol) and cyclic (1324 g/mol) synthetic analogues. The full peptide sequence was identified as inserted in a putative conserved domain of late-embryogenesis proteins which produced a significant alignment hit (100% of identity and E-value of 1e-05) with a hypothetical protein JCGZ_12502 off. curcas. Whereas in the linear peptide predominated the double charged ion state (m/z 671.68), in the cyclic form was observed the mono charged ion state (m/z of 1325.19) and an unusual MS/MS fragmentation pattern. The differences between the forms were discrete in terms of ionic mobility, retention time (reverse phase) and net charge as function of pH. Circular dichroism spectra presented an intense negative peak at 198 nm which is assigned for its disordered contents. A negative peak at 222 nm in the spectrum of the circular form suggested its structure was not as disordered as the linear form. The peptides were neither haemolytic nor cytotoxic and did not inhibit phytopathogenic fungi. Surprisingly, the circular but not the linear peptide increased the proteolytic activity of papain. (C) 2015 Elsevier Ltd. All rights reserved.