Specific inactivation of TRH after its release. Release of the N-terminal pyroglutamyl group from pGlu-|-His-Xaa tripeptides and pGlu-|-His-Xaa-Gly tetrapeptides. Binds 1 zinc ion per subunit. Homodimer; disulfide-linked. Predominantly expressed in brain and pituitary. Lower levels in lung and liver. Belongs to the peptidase M1 family.