Interactions of cyclic AMP and its dibutyryl analogue with model membrane:X-ray diffraction and Raman spectroscopic study using cubic liquid-crystalline phases of monoolein

Interactions of adenosine 3':5'-cyclic monophosphate (cAMP) and its dibutyr yl analogue, N-6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dbcAMP ), with a lipid bilayer were studied by small-angle X-ray diffraction (SAXD ) and Raman spectroscopy. The cubic Pn3m phase of monoolein (MO) served as a bilayer-based model system. SAXD measurements have indicated that incorpo ration of approximately 3 wt.% cAMP leaves the phase parameters practically unaltered, whereas the same content of dbcAMP induces the intercubic Pn3m- ->Ia3d transition. By applying the concepts of lipid shape parameter and in finite periodic minimal surface to these MO phases, we have suggested that, as opposed to cAMP, dbcAMP associates with the MO bilayer. This conclusion has been supported by the different effects of phase matrix on the Raman s hifts of the adenine and phosphate vibrational modes of these two nucleotid es. Moreover, Raman spectra have indicated that dbcAMP inserts into the bil ayer through the butyryladenine group, positioning dbcAMP preferentially at the polar/apolar interface. (C) 2001 Elsevier Science B.V. All rights rese rved.