Aminopeptidases Isolated from Cotyledons of Cowpea, Vigna unguiculata

Three aminopeptidases have been separated from cotyledon extracts from cowpea, Vigna unguiculata (L.) Walp., and numbered in order of decreasing affinity for the anion exchange medium DEAE-Sephacel. API showed a wide acceptance of model substrates, with highest activity under standard conditions against arginyl β-naphthylamide (NA). AP2 did not act on basic substrates and preferred phenylalanyl β-NA. AP3 displayed the narrowest substrate specificity, with strong activity against only alanyl β-NA and glycyl β-NA. The chelator 1,10-phenanthroline completely or almost completely inhibited forms AP1 and AP3, whereas AP2 was insensitive to phenanthroline at the same concentration (5 mM). All three aminopeptidases were totally inhibited by Ag+ or Zn2+ ( ≤ 0.5 mM).