The degradation of a nonapeptide, sleep inducing peptide, in rat brain: comparison with enkephalin breakdown.

The degradation of delta sleep inducing peptide (DSIP) was studied and compared with that of Met-enkephalin in brain homogenates. After 7.5 minutes of incubation of 2.5% (w/v) homogenate, 30% of N-terminal tryptophan was released from DSIP, while 75% of N-terminal tyrosine was released from Metenkephalin. The optimal pH of degradation of both peptides was pH 7.35. A rapid increase of breakdown of the peptides was observed during the 10 days of postnatal growth, with breakdown expressed per unit weight of brain. Neither morphine nor deprivation of rapid eye movement (REM) sleep affected the degradation of peptides.