Definition
a-Casein exorphins are peptides isolated from a-Casein1. They have morphine-like opioid (narcotic) activity and hence are termed exorphins1.
Discovery
a-Casein exorphins were first purified from pepsin treated hydrolysates of a-Casein1. Their opiod activity was then determined by biochemical assays1.
Classification
a-Casein exorphins belong to the class of opioid peptides that also includes exorphins that are proteins absorbed by the digested food and endorphins that are produced by the body itself1.
Structural Characteristic
They correspond to the sequences 90-96, Arg-Tyr-Leu-Gly-Tyr-Leu-Glu, and 90-95, Arg-Tyr-Leu-Gly-Tyr-Leu, of alpha-casein2. Two analogues of a-Casein exorphins, Tyr-Leu-Gly-Tyr-Leu-Glu (91-96) and Tyr-Leu-Gly-Tyr-Leu (91-95), have now been synthesized and characterized. They are all resistant to the action of trypsin2.
Mode of action
Not much is known about the mode of action of a-Casein exorphins. One study has indicated that these peptides may be efficient ligands for copper ions3.
Functions
a-Casein exorphins may have gastrointestinal and even neuronal functions1
References
1.Zioudrou C, Streaty RA, Klee WA (1979). Opioid peptides derived from food proteins. The exorphins. J Biol Chem., 254(7), 2446-9.
2.Loukas S, Varoucha D, Zioudrou C, Streaty RA, Klee WA (1983). Opioid activities and structures of alpha-casein-derived exorphins. Biochemistry, 22(19), 4567-73.
3.Lodyga-Chruscinska E, Micera G, Szajdzinska-Piêtek E, Sanna D (1998). Copper(II) Complexes of Opiate-like Food Peptides. J Agric Food Chem., 46(1), 115-118.
