Degradation of dynorphin-related peptides by the puromyein-sensitive aminopeptidase and aminopeptidase M

The degradation of dynorphin-related peptides by the puromycin-sensitive aminopeptidase and aminopeptidase M was examined using these peptides as alternate substrate inhibitors. K_i determinations showed that both aminopeptidases exhibit a higher affinity for longer dynorphin-related peptides, i.e., K_i for dynorphin A-17 = 23-30 nM with the K_i increasing to 25-50 μM for the enkephalin pentapeptides. Binding appears dependent not only on peptide length, but also on its sequence. With aminopeptidase M, as the peptide size increases from five to 10 amino acids, k_cat remains relatively constant; however, as the peptide size increases beyond a decapeptide, k_cat decreases significantly. With the puromycin-sensitive aminopeptidase, similar results were obtained except that k_cat was greatest for the pentapeptide. Thus, if one considers k_cat/K_m as the relevant kinetic constant for estimating in vivo peptide hydrolysis, these results are consistent with the involvement of aminopeptidase M and the puromycin-sensitive aminopeptidase in the degradation of extended dynorphin-related peptides.