Enkephalin L is an opioid peptide. Opioid peptides are a group of neuropeptides which include enkephalins, endorphins and dynorphins. In addition to their central and peripheral antinociceptive function, opioids can modulate immune activity and cell proliferation. Enkephalins typically have a turnover rate measured in seconds to minutes, both in vivo and in vitro, and this stability is related to the age of the cell system under study. It is noteworthy that the residues most essential to enkephalin function are also either neurotransmitters themselves (glycine) or immediate precursors of L-Dopa, dopamine and norepinephrine (tyrosine and phenylalanine). The variable fifth amino acid leucine (leu5) or methionine (met5) has not yet been assigned any neurotransmitter candidacy. Again, this suggests that enkephalin is polyfunctional in that, in its intact state it elicits binding to the same sites in the brain as morphine and other opiates, and its degradation products have a potential for follow-up accessory functions by reacting as signaling entities themselves, or as the immediate precursors to inhibitory or metabotropic neurotransmitters. Enkephalins are present in macrophages infiltrating the dermal papillae in involved psoriatic skin and that the amount of enkephalin is significantly increased in involved psoriatic skin. Major enkephalin pathways in the brain involve the extrapyramidal system, including motor pathways controlled by the basal ganglia, the limbic system that governs emotional and behavioral control, and the hypothalamic-neuroendocrine axis. The apparent overlap of localization within the central nervous system of dopaminergic, glycinergic, and enkephalinergic pathways is speculated to be of neurophysiological significance, especially in light of the relatively short half-life of the enkephalins and the immediate precursor-product relationship between tyrosine and dopamine, and glycinergic signaling. Enkephalins are released into the bloodstream of mammals by the adrenal medulla. Once they are in the blood, these peptides undergo a fairly rapid hydrolysis by several plasma-contained enzymes. However, a fraction of the enkephalins present in the plasma are bound to the serum albumin, and the bound peptides are almost completely intact even after a long incubation in the presence of serum enzymes. (PMID: 9450624, 16802191, 4069309).