Planarian peptidylglycine‐hydroxylating monooxygenase, a neuropeptide processing enzyme, colocalizes with cytochrome b 561 along the central nervous system

Planarians are one of the simplest animal groups with a central nervous system. Their primitive central nervous system produces large quantities of a variety of neuropeptides, of which many are amidated at their C terminus. In vertebrates, peptide amidation is catalyzed by two enzymes [peptidylglycine α‐hydroxylating monooxygenase (PHM) and peptidyl‐α‐hydroxylglycine α‐amidating lyase] acting sequentially. In mammals, both enzymatic activities are contained within a single protein that is encoded by a single gene. By utilizing PCR with degenerate oligonucleotides derived from conserved regions of PHM, we succeeded in cloning a full‐length cDNA encoding planarian PHM. The deduced amino acid sequence showed full conservation of five His residues and one Met residue, which bind two Cu atoms that are essential for the activity of PHM. Northern blot analysis confirmed the expression of a PHM mRNA of the expected size. Distribution of the mRNA was analyzed by in situ hybridization, showing specific expression in neurons with two morphologically distinct structures, a pair of the ventral nerve cords and the brain. The distribution of PHM was very similar to that of cytochrome b 561 . This indicates that the ascorbate‐related electron transfer system operates in the planarian central nervous system to support the PHM activity and that it predates the emergence of Plathelminthes in the evolutionary history.