Depth-dependent analysis of membranes using benzophenone-based phospholipids

Any attempt to probe the membrane hydrophobic core with chemical reagents n ecessitates the use of reactive intermediates like carbenes and nitrenes, w hich can insert into C-H bonds. Several photoactivable reagents based on ca rbenes and nitrenes have been reported. However, the high reactivity of the se reagents, often leads to very low insertion yields. We report here a hig h degree of cross-linking (35-40%) achieved with three benzophenone-based p hospholipids and analyze the carbon functionalization data using a multiple Gaussian function. These phospholipids are so designed so as to permit dep th-dependent labeling in membranes. Single bilayer vesicles were prepared f rom these phospholipids and dimyristoylphosphatidylcholine. The cross-linke d product was isolated and characterized by mass spectroscopy. The results obtained indicated that the cross-linked product was dominated by dimeric p roduct formed by intermolecular cross-linking. The Gaussian analysis used h ere provides insight into the relative depths of the probes inside the memb rane. (C) 2000 Elsevier Science B.V. All rights reserved.