Proenkephalin (PENK), formerly known as proenkephalin A (since proenkephalin B was renamed prodynorphin), is an endogenous opioid polypeptide hormone which, via proteolyic cleavage, produces the enkephalin peptides met-enkephalin, and to a lesser extent, leu-enkephalin. [5] Upon cleavage, each proenkephalin peptide results in the generation of four copies of Met-enkephalin, two extended copies of met-enkephalin, and one copy of leu-enkephalin. [5] Contrarily, Leu-enkephalin is predominantly synthesized from prodynorphin, which produces three copies of it per cleavage, and no copies of Met-enkephalin. Other endogenous opioid peptides produced by proenkephalin include adrenorphin, [6] amidorphin, [7] BAM-18, [8] BAM-20P, [9] BAM-22P, [9] peptide B, [10] peptide E, [11] and peptide F. [12]
Proenkephalin is produced by the medium spiny neurons of the striatum which undergo neurodegeneration in early stages of Huntington's disease (HD). PENK [13] and related peptides [14] [15] measured in cerebrospinal fluid are proposed as potential biomarkers of disease progression in HD. Furthermore, PENK has been found associated with acute kidney injury [16] and glomerular filtration rate in steady-state and critically ill patients. [17] [18]