Isolation of a heptapeptide Val‐Val‐Tyr‐Pro‐Trp‐Thr‐Gln (valorphin) with some opiate activity

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Abstract
Bovine hypothalamic tissue was extracted and purified by solid phase extraction and several reversed-phase HPLC steps. The amino acid sequence of the purified peptide was determined by Edman degradation to be Val-Val-Tyr-Pro-Trp-Thr-Gln. This was confirmed by comparison of its chromatographic behavior with that of the synthetic peptide, and mass spectrometric analysis resulted in a mass identical to the calculated mass for this peptide. This heptapeptide shows homology with residues 32-38 of the beta-chain of bovine hemoglobin. The peptide inhibited the electrically induced contractions of the guinea pig ileum muscle preparation; this inhibition was reversible by naloxone. It also inhibited the binding of 125I-DAMGO (selective for μ receptors) to rat brain with an IC50 of 10 μm and the binding of 3H-DPDPE (selective for σ receptors) with an IC50 of 185 μm. With two valines at the N-terminus and some opiate activity, valorphin seems a suitable name for this newly isolated peptide.