The arginine-specific reagent phenylglyoxal has been used to identify a hyper-reactive arginine residue which is essential for activity in the type II dehydroquinases of Streptomyces coelicolor and Aspergillus nidulans. Electrospray mass spectrometry was used both to characterise the phenylglyoxal modified protein, and to identify the phenylglyoxal modified peptides following enzymatic digestion. The advantages of using electrospray mass spectrometry for monitoring arginine modication aimed at identifying functional residues in proteins are discussed.
