Cotranslationally removes the N-terminal methionine from nascent proteins. The N-terminal methionine is often cleaved when the second residue in the primary sequence is small and uncharged (Met-Ala-, Cys, Gly, Pro, Ser, Thr, or Val). Plays the major role in N-terminal methionine removal. Less efficient when the second residue is Val. Release of N-terminal amino acids, preferentially methionine, from peptides and arylamides. Binds 2 divalent metal cations per subunit. Has a high-affinity and a low affinity metal-binding site. The true nature of the physiological cofactor is under debate. The enzyme is active with cobalt, zinc, manganese or divalent iron ions. Most likely, methionine aminopeptidases function as mononuclear Fe(2+)-metalloproteases under physiological conditions, and the catalytically relevant metal-binding site has been assigned to the histidine-containing high-affinity site. In contract to the MetAP 2 isoform, is not inhibited by the fungal metabolite fumagillin, an antiangiogenic drug. kcat is 1173, 1416 and 507 min(-1) with a Met-Ala-Ser, a Met-Gly-Met-Met and a Met-Ala-Ser-Trp peptide substrate, respectively. Associates with the 60S ribosomal subunit of the 80S translational complex. Present with 19600 molecules/cell in log phase SD medium. Belongs to the peptidase M24A family. Methionine aminopeptidase type 1 subfamily.