Aminopeptidase which preferentially removes N-terminal Arg and Lys residues from peptides and proteins. Release of N-terminal Arg and Lys from oligopeptides when P1' is not Pro. Also acts on arylamides of Arg and Lys. Binds 1 zinc ion per subunit. No activity with L-Asp-pNA, L-Glu-pNA or D-Leu-pNA. Despite its similarity to leukotriene hydrolases, AP-1 does not have leukotriene hydrolase activity. One of the mammalian leukotriene binding sites, 'Tyr-378', is replaced by a Phe residue in AP-1. Belongs to the peptidase M1 family.