The hemorphins: a new class of opioid peptides derived from the blood protein hemoglobin.

Hemorphins are endogenous peptides belonging to the family of "nonclassical" or "atypical" opioid peptides. They are generated by enzymatic hydrolysis of the beta-, kappa-, delta-, or epsilon-chain of the blood protein hemoglobin. Originally, the hemorphins were isolated from enzymatically treated bovine blood. In recent years hemorphin structures have been identified as naturally occurring peptides in brain, plasma, and cerebrospinal fluid. This article will review recent studies of the hemorphins regarding their structures, mechanisms for their release, and their biological actions. A particular emphasis will be directed to their role in exercising human and their clinical relevance.