Peptidylglycine alpha-amidating monooxygenase catalyzes the oxidative cleavage of glycine extended peptides at their terminus. In the course of the reaction, there is a requisite long-range electron transfer between the two copper centers (CuH and CuM) located in the hydroxylating domain. This communication presents data that argue against the participation of the extended peptide backbone of substrate in the long-range electron transfer. We propose that electron transfer occurs via the bulk solvent that separates CuH from CuM.