Interactions of angiotensin II with membranes using a combination of differential scanning calorimetry and 31P NMR spectroscopy

Summary This study of angiotensin II (ANG II) membrane interactions uses a combination of³¹P NMR spectroscopy and differential scanning calorimetry (DSC), two valuable and complementary techniques which can provide useful information about the thermotropic and dynamic properties of peptide hormones in membranes. The major conclusion from the calorimetric experiments is that ANG II affects the phase properties of hydrated dipalmitoyl-phosphatidylcholine (DPPC) bilayers by mainly broadening the pretransition area. Preliminary³¹P NMR data seem to confirm the DSC results by showing that ANG II produces a lowering of the pretransition temperature but affects only minimally the main phase transition. In combination, the results from the two methods may indicate that the hormone produces its effects on the phospholipid head groups while its effects on the bilayer alkyl chains are not significant. Such results can be interpreted to mean that ANG II closely interacts with the phospholipid head groups perhaps up to the level of the interface, but does not enter deeper into the membrane bilayer.