Conformational effects on the fluorescence of pyrene-labeled alkyldiacyl glycerols in different model membranes.

We synthesized two isomeric alkyldiacyl glycerols containing pyrene as a fluorescent reporter group bound to the omega end of both acyl chains. If located in the phospholipid monolayer of a vesicle both isomers showed intramolecular pyrene excimer fluorescence, indicating parallel orientation of both pyreneacyl chains in the lipid molecule. In micelles only pyrene monomer fluorescence was observed. Thus, in this system the labeled lipids adopt a conformation with both pyreneacyl chains extending into different directions. Using vesicles, lipase activities could be continuously determined from the increase of pyrene monomer fluorescence.