Met-enkephalin is a naturally occurring peptide, a chemical messenger made of linked amino acids, that plays a part in fundamental biological processes. This internal substance helps regulate various bodily functions. Understanding its presence and actions provides insight into how the body manages its own internal chemistry.
Understanding Met-Enkephalin
Met-enkephalin is a small protein fragment known as a pentapeptide, composed of five amino acids. Its precise sequence is tyrosine, glycine, glycine, phenylalanine, and methionine, often abbreviated as Tyr-Gly-Gly-Phe-Met. This specific arrangement of amino acids gives met-enkephalin its unique properties and functions within the body. It is one of two primary forms of enkephalin, the other being leu-enkephalin, which differs by only one amino acid at its end.
This molecule originates from a larger precursor protein called proenkephalin. Through a process involving two metabolic steps, proenkephalin undergoes enzymatic cleavage to yield met-enkephalin. Enzymes such as prohormone convertase 1 or 2 first reduce proenkephalin, and then carboxypeptidase E further processes the resulting intermediates.
Where Met-Enkephalin Acts
Met-enkephalin is found widely distributed throughout the body, with significant concentrations in the central nervous system, including various brain regions and the spinal cord. It is also present in cells of the adrenal medulla, a gland involved in stress responses.
The molecule exerts its effects by binding to specific structures on cell surfaces known as receptors. Met-enkephalin primarily acts as an agonist for delta-opioid receptors. It also binds to mu-opioid receptors, though to a lesser extent. Additionally, met-enkephalin interacts with the opioid growth factor receptor, also referred to as the zeta-opioid receptor. These interactions trigger diverse cellular pathways.
Its Diverse Roles in the Body
Met-enkephalin initiates a variety of physiological responses. A well-recognized function is its involvement in pain sensation, where its activation of opioid receptors can lead to pain relief. This analgesic effect is similar to that of other opioid compounds.
Beyond pain modulation, met-enkephalin also influences mood, contributing to antidepressant-like responses through its interactions with opioid receptors in the brain. Furthermore, its binding to the opioid growth factor receptor plays a role in regulating tissue growth and regeneration, influencing cell proliferation.
Met-enkephalin is also implicated in the body’s response to stress. Research indicates its activity may increase in brain regions such as the hippocampus and prefrontal cortex during stressful conditions. These areas are involved in memory, learning, and executive functions, suggesting met-enkephalin helps modulate the brain’s adaptation to stress. Its influence extends to modulating neurotransmission, affecting the release of chemicals like dopamine and GABA in reward pathways.
Why Met-Enkephalin Is Not a Drug
Despite its varied and beneficial roles, met-enkephalin is not suitable for direct use as a medicine. This limitation stems from its rapid breakdown within the body by several enzymes, sometimes called enkephalinases, which quickly metabolize it. These enzymes include aminopeptidase N, neutral endopeptidase, dipeptidyl peptidase 3, carboxypeptidase A6, and angiotensin-converting enzyme.
This rapid enzymatic degradation results in very low bioavailability, meaning only a small fraction reaches its target sites when administered externally. It also possesses a very short half-life, typically lasting only a few minutes in the body. These properties make it impractical for therapeutic purposes, preventing its direct application as a pharmaceutical agent.