Identification of the five essential histidine residues for peptidylglycine monooxygenase.

Peptidylglycine monooxygenase (PGM) is a copper-containing monooxygenase that plays a key role in the peptide C-terminal alpha-amidation. Comparative analysis of the amino acid sequences of rat, human, bovine and frog PGMs revealed that ten histidines (residues 107, 108, 172, 235, 242, 244, 279, 364, 366 and 367 in rat PGM) are conserved among the four species. We introduced site-directed mutations to the ten histidines of rat PGM and found that the mutation of His- 107-->Ala, His-108-->Ala, His-172-->Ala, His-242-->Arg or His-244-->Ala abolished the enzyme activity. The five mutant proteins lacking the enzyme activity bound to a substrate, Phe-Gly-Phe-Gly, as did the wild type PGM. These results along with available evidence indicate that the five histidine residues (His-107, 108, 172, 242 and 244) are essential for PGM activity, acting as copper ligands.