Catalyzes the hydrolysis of a range of N-terminal amino acids. Release of N-terminal Arg and Lys from oligopeptides when P1' is not Pro. Also acts on arylamides of Arg and Lys. Release of an N-terminal amino acid, preferentially leucine, but not glutamic or aspartic acids. Binds 2 Zn(2+) ions per subunit. Optimum pH is 8-9. Stable for 20 min at temperatures of up to 80 degrees Celsius. Monomer. Belongs to the peptidase M28 family. M28B subfamily.