The kinetic parameters of selected homologous substrates, referenced to kcat/Km of L-hArg (100%, blue) and 1/Km of L-Nva (100%, red). Among alkyl derivatives (L-Ala, L-Abu, L-Nva, L-Nle), medium size nPr side chain of L-Nva is the most preferentially bound in the S1 cavity, although L-Ala-ACC is processed at a higher hydrolysis rate. Other examples show a significance of the P1 residue structure extension: CH2 elongated analogs (homo) are generally better recognized and faster cleaved than their natural counterpart.