Labeling and Protecting <italic>N</italic>‐Terminal Protein Positions by <italic>β</italic>‐Peptidyl Aminopeptidase‐Catalyzed Attachment of <italic>β</italic>‐Amino‐Acid Residues – Insulin as a First Example.

We have shown for the first time that a natural protein (human insulin) can be acylated at the <italic>N</italic>‐terminus with a <italic>β</italic>‐amino acid (H‐<italic>β</italic>³hAla‐), in a process catalyzed by the <italic>β</italic>‐peptidyl aminopeptidase 3‐2W4‐BapA. This selective modification, which could also be applied for protein labeling and tagging, should be generally useful, also to protect peptides and proteins from attack by common aminopeptidases. [ABSTRACT FROM AUTHOR]