Opioid peptide

Opioid Peptides are short sequences of amino acids which mimic the effect of opiates in the brain. Opioid peptides may be produced by the body itself, for example endorphins, or be absorbed from partially digested food (casomorphins, exorphins and rubiscolins). The effect of these peptides vary, but they all resemble opiates. The opioid food peptides have lengths of typically 4-8 amino acids. The body's own opioids are generally much longer.

Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, and the control of food intake.

Opioid peptides produced by the body
The human genome contains three homologous genes that are known to code for endogenous opioid peptides. Each gene codes for a large protein that can be processed to yield smaller peptides that have opiate-like activity.
 * The nucleotide sequence of the human gene for proopiomelanocortin (POMC) was characterized in 1980 . The POMC gene codes for endogenous opiates such as β-endorphin and gamma-endorphin . The peptides with opiate activity that are derived from proopiomelanocortin comprise the class of endogenous opioid peptides called "endorphins".
 * The human gene for enkephalins was isolated and its sequence described in 1982.
 * The human gene for dynorphins (originally alled the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983.

Opioid food peptides

 * Casomorphin (from milk)
 * Gluten exorphin (from gluten)
 * Gliadorphin/gluteomorphin (from gluten)
 * Rubiscolin (from spinach)

Opioid peptides of microbial origin

 * Deltorphin I and II (fungal)
 * Dermorphin (from an unknown microbe)