Labeling and Protecting N-Terminal Protein Positions by -Peptidyl Aminopeptidase-Catalyzed Attachment of -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 N-terminus with a -amino acid (H-(3)hAla-), in a process catalyzed by the -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.