The in vitro interaction of delta-sleep-inducing peptide with cell membranes

The effect of delta-sleep-inducing peptide (DSIP) on erythrocytic membranes of human donor blood was studied by the spin label and spin probe methods. The spin-labeled derivative of DSIP containing the N-terminal residue of 1 -oxyl-2,2,5,5-tetramethylpyrroline-3-carboxylic acid was synthesized. An an alysis of the ESR spectra of the spin-labeled DSIP derivative recorded afte r its incubation with a human erythrocyte suspension at 37 degrees C reveal ed a decrease in the rotational correlation time (tau(c)) and molecular ord er parametel (S) in comparison with the control solutions of the peptide in phosphate buffer (pH 7.4). The application of paramagnetic probes, 5-, 12- , and 16-doxylstearic acids and 3-doxylandrostanol, demonstrated that the i ntroduction of DSIP in an erythrocytic suspension significantly increased t he mobility of the hydrophobic area of the membrane bilayer both at a depth of 10-22 Angstrom and in the subsurface area (4-6 Angstrom). The dependenc e of these effects on the DSIP concentration was shown to have the form of a curve with well-defined extremes. The maximal disordering of membrane lip ids was observed at peptide concentrations of 10(-9) and 10(-6) M. These re sults suggested that significantly affected the structure of plasmatic memb ranes in vitro by changing the physical state of their lipid components.