A photochemical technique for measuring lateral diffusion of spin-labeled phospholipids in membranes

A technique is described for the measurement of lateral diffusion of any spin-labeled molecule in planar phospholipid multilayers, using low probe concentrations and a photochemical reaction to generate the initial concentration gradient. Features of the technique include simplicity of data analysis, versatility, and applicability over a wide range of motional rates. Measurements have been made on dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine in the fluid phase (using a phospholipid with head-group spin label), and excellent agreement is found with recent nuclear magnetic resonance spin-echo measurements, as well as with other spin-label and fluorescence photobleaching results.