Scientists found that a sleep‑related peptide called DSIP naturally occurs in sheep pineal glands and can stick to larger proteins without forming a chemical bond. They used various lab techniques to separate and identify the peptide and showed it can exist both on its own and attached to big protein molecules.

The nonapeptide delta-sleep-inducing peptide (DSIP) has been isolated from venous blood of rabbits induced to sleep. Numerous reports have described sleep as well as extra-sleep effects. Radiochemical and immunochemical data suggest a relationship of DSIP with the pineal gland supported by interactions of this peptide with pineal functions such as the serotonin N-acetyltransferase activity. In order to demonstrate the natural occurrence of DSIP-like material associated with high Mr proteins in the ovine pineal, organs were water-extracted and fractionated by ultrafiltration and gel filtration. Radioimmunoassay (RIA) for DSIP-like fragments of the fractions revealed considerable amounts of pineal DSIP-like immunoreactivity (DSIP-LI) apparently existing in small as well as large molecular forms. Acidification of large DSIP-LI forms resulted in the elution from Sephadex G-50 of Mr less than or equal to 1,000 DSIP-like material. This free DSIP-LI form coeluted with the synthetic DSIP nonapeptide from microBondapak C18 on high-performance liquid chromatography. The results, therefore, appear to indicate the presence of a (biospecific) noncovalent intermolecular interaction of DSIP (1-9) with proteins (Mr greater than or equal to 10,000) of the ovine pineal gland.