N-terminal labeling of proteins by the Pictet–Spengler reaction

The Pictet–Spengler reaction was applied to the N-terminal labeling of horse heart myoglobin. This was performed in the following two steps: (1) conversion of the N-terminal glycine residue to an α-keto aldehyde by a transamination reaction and (2) condensation of the resulting activated myoglobin with tryptamine analogues by the Pictet–Spengler reaction. Ultraviolet (UV)/visible (vis) absorption and circular dichroism (CD) spectral data revealed that the tertiary structure of myoglobin was not altered by the Pictet–Spengler reaction.