An Infrared Investigation of Palmitoyl‐Coenzyme A and Palmitoylcarnitine Interaction with Perdeuterated‐Chain Phospholipid Bilayers

Mixtures of di‐(perdeuteropalmitoyl)‐ sn ‐glycero‐3 choline ([ 2 H 62 ]Pam 2 Gro P Cho) with palmitoylcarnitine or palmitoyl‐CoA in aqueous suspension have been examined by Fourier‐transform infrared spectroscopy. The C‐H (or C‐D) region of the spectrum shows that an order‐disorder transition exists in pure aqueous palmitoylcarnitine at 45°C; palmitoylcarnitine mixes with [ 2 H 62 ]Pam 2 Gro P Cho without perturbing the gel‐fluid transition of the phospholipid even at [ 2 H 62 ]Pam 2 Gro P Cho palmitoylcarnitine 1:2 molar ratios; and palmitoyl‐CoA, however, at similar proportions, smears out the [ 2 H 62 ]Pam 2 Gro P Cho transition as detected from C‐D stretching vibrations. Relevant data from the carbonyl region include; the high‐frequency (non‐hydrogen bound) carbonyl subpopulation, but not the low frequency one, detects the gel‐to‐fluid transition of the phospholipid; the carbonyl region detects the thermotropic transition over a wider temperature range than the methylene stretching region, i.e. detects changes starting well below and ending several degrees above the methylene transition temperature, and a significant interaction may occur between some coenzyme A group and the carbonyl groups of the phospholipid. The latter interaction may contribute to explain the coenzyme A/carnitine exchange during mitochondrial fatty acid import.