What Is DSIP? The Delta Sleep-Inducing Peptide and Its Open Questions

What DSIP is

Delta sleep-inducing peptide, abbreviated DSIP, is a nonapeptide with the sequence Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu.^[1] It was isolated from rabbit cerebral venous blood by a group in Basel in 1977 and was initially regarded as a candidate sleep-promoting factor.^[2] Its molecular weight is given as 849 in an early review,^[3] and the Sealed Peptides product lists 848.8 Da.

The name records the original observation, not an established function. As the sections below show, the literature itself treats the function as an open question.

The original characterization

The 1977 characterization is a useful example of how a peptide was identified. A peptide that enhanced delta and spindle patterns on the electroencephalogram after infusion into the brain ventricles of rabbits was isolated and sequenced. The authors then made the peptide synthetically, together with five possible metabolic fragments, two analogues with exchanged amino acids and a related tripeptide, and tested all nine under double-blind conditions in 58 rabbits. Only the synthetic DSIP itself showed significant and specific enhancement of delta and spindle patterns.^[1]

That experiment established that a defined chemical structure, and not some other component of the isolate, was responsible for the effect in that rabbit system. It did not establish a role for the peptide in any other species or setting.

What the literature calls unresolved

A 2006 mini-review titled “a still unresolved riddle” states the problem plainly. The link between DSIP and sleep was never further characterized, in part because the DSIP gene, protein and possible related receptor were never isolated. The authors describe the hypothesis that DSIP is a sleep factor as poorly documented and weak, say that its natural occurrence and biological activity remain obscure, and note that its structure differs from that of any known peptide family.^[2]

The same review proposes that a DSIP-like peptide, rather than DSIP itself, may account for at least part of the immunoreactivity and activity attributed to it, partly on the basis that certain artificial structural analogues, but not DSIP itself, promoted slow-wave sleep in rabbits and rats in the authors’ early studies.^[2] An earlier review reported DSIP-like immunoreactivity in brain, in peripheral organs and in the plasma of several mammals, and noted that the peptide had been observed to affect many other measured variables beyond sleep.^[3]

For a reader the useful lesson is about evidence. A short peptide can be well characterized as a molecule while its biology remains unsettled, and the two should not be confused. The chemistry on this page is on firm ground; claims about function are not, and this page makes none.

Chemistry at a glance

The listed molecular formula is C35H48N10O15. The average mass calculated from it is 848.82 g/mol, in agreement with the listed weight, and the monoisotopic mass is 848.330, so a singly protonated ion would be expected near m/z 849.34.

The sequence has two acidic residues, aspartate and glutamate, and no lysine, arginine or histidine. It contains tryptophan and no tyrosine, cysteine or methionine. Those facts matter when choosing a solvent, because the charge on a peptide depends on the pH of the solution relative to its isoelectric point, and a peptide with only acidic side chains will behave differently from a basic one. The solubility and aggregation guide explains the general principle.

Checking the mass from the sequence

Because DSIP is short and its sequence is fixed, its mass can be built up residue by residue. The monoisotopic residue masses are 186.0793 for tryptophan, 71.0371 for each of two alanines, 57.0215 for each of three glycines, 115.0269 for aspartate, 87.0320 for serine and 129.0426 for glutamate. They sum to 830.3195, and adding one water (18.0106) gives 848.3301 Da, the figure obtained from the formula. The peptide molecular weight estimator returns the same value for the sequence WAGGDASGE.

A doubly charged ion of this peptide would appear near m/z 425.17. As with any identity check, agreement of the observed and expected masses shows that the main component has the right composition, but it does not by itself show the order of the residues, which is what tandem mass spectrometry is used for.

Analytical notes for the bench

Tryptophan makes this peptide easier to detect than many of its size. Tryptophan contributes about 5,500 M⁻¹ cm⁻¹ to absorbance at 280 nm,^[4] and at 214 nm its molar extinction coefficient is roughly thirty times that of the peptide bond.^[5] A single tryptophan therefore dominates the ultraviolet signal, so a UV-based concentration estimate is sensitive to anything that alters that residue. The extinction coefficient entry in the glossary defines the quantity, and reconstitution math explains how a measured absorbance is compared with a calculated concentration.

Identity and purity checks follow the usual pattern, as described in mass spectrometry and peptide identity and reading an HPLC chromatogram. The DSIP research overview lists the compound’s cited literature, and this page, like that one, does not describe or endorse any use of the material.