How bradykinin alters the lipid membrane structure: A spin label comparative study with bradykinin fragments and other cations

Electron spin resonance spectroscopy of several different spin labels was u sed to comparatively study the interaction of the cationic peptide hormone bradykinin (BK; Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg), and some BK fragments (des-Arg(9)-BK, des-Arg(1)-BK, and Arg-Pro-Pro-Gly-Phe or BK1-5), with ani onic vesicles of dimyristoyl phosphatidylglycerol (DMPG). For temperatures above the lipid gel-liquid crystal thermal transition (T-m approximate to 2 0 degrees C), membrane-incorporated spin labels indicated that all peptides (total concentration of 10 mol % relative to lipid) interact with the bila yer, turning the membrane less fluid both at its surface and center, sugges ting a partial penetration of the peptides into the membrane core. However, in the lipid gel phase (t < T-m), BK was found to display a much stronger interaction with the membrane decreasing the bilayer fluidity. At temperatu res around 15 degrees C the BK-DMPG system was found to present a hysteresi s, evinced by the different electron spin resonance spectra yielded upon co oling and heating the sample. System reversibility was found at all other t emperatures (0-45 degrees C). That effect could not be assigned to the BET higher concentration at the membrane surface due to its higher net charge ( 2(+)) compared to the fragments (1(+)), because ten times more des-Arg(9)-B K (100 mol %) yielded opposite result. Further, that was found to be a resu lt rather different from those elicited by the other cations tested: the mo novalent Na+, the divalent Zn2+, and the peptide pentalysine. The data pres ented here are discussed in the light of the different BK and BK fragments biological activities. (C) 2000 John Wiley & Sons, Inc.