Catalysis of the hydrolysis of a single N-terminal amino acid residue from a polypeptide chain by a catalytic mechanism that involves a catalytic triad consisting of a serine nucleophile that is activated by a proton relay involving an acidic residue (e.g. aspartate or glutamate) and a basic residue (usually histidine).
Source:
https://www.ebi.ac.uk/merops/about/glossary.shtml#CATTYPE,
https://www.ebi.ac.uk/merops/about/glossary.shtml#AMINOPEPTIDASE