N-terminal L-aspartyl-[protein] + N-acetyl-L-methionine => N-terminal N(alpha)-acetyl-L-methionyl-L-aspartyl-[protein] + H2O
n-terminal l-aspartyl-[protein] + n-acetyl-l-methionine => n-terminal n(alpha)-acetyl-l-methionyl-l-aspartyl-[protein] + h2o