QC (Glutaminyl Cyclase) is an important enzyme responsible for converting glutaminyl peptides into pyroglutamyl peptides, which are critical precursors of NMDA receptor agonists. QC is primarily located in neurons and glial cells, participating in glutamate metabolism and neurotransmitter generation. By regulating NMDA receptor activity, QC is involved in biological responses and signaling pathways such as learning, memory, and neuroplasticity. The expression of the QC gene is tissue-specific, and mutations or abnormal expression are associated with various neurological disorders, such as Alzheimer's disease and schizophrenia.