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). Requires deformylation of the N(alpha)-formylated initiator methionine before it can be hydrolyzed (By similarity). May play a role in colon tumorigenesis. 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. Optimum pH is 7.5-8.0. Overexpressed in colon cancer cell lines and colon tumors as compared to normal tissues (at protein level). Belongs to the peptidase M24A family. Methionine aminopeptidase type 1 subfamily. It is uncertain whether Met-1 or a Met upstream of this sequence is the initiator.