To compare peptide sequences, various amino acid descriptors were evaluated, including: z-scales (3) and z-scales (5) with 3 and 5 dimensions respectively , DPPS (4) and DPPS , ISA-ECI (2) , and E-descriptors (5) . In the present study, the descriptors were used to transform the peptide sequences into vectors that can be used as input for the kernel function. Despite their simplicity, the main disadvantages are 1) the inability to do a bitwise comparison of peptide sequences of different lengths, since the dimensions of the vectors directly depend on the number of amino acids in the sequences, 2) the use of descriptors limit the use of non-natural amino acids for which they have to be calculated and 3) their applicability limited to linear peptides.