Hydrolyzes di-, tri- and tetrapeptides with a lysine as the N-terminal amino acid and with Gly, Lys, Ala, Phe or Glu in the second position. Preferentially, release of N-terminal lysine. Binds 2 Zn(2+) ions per subunit. Optimum pH is 8. Optimum temperature is 100 degrees Celsius. Homotetramer. Belongs to the peptidase M42 family.