An infrared investigation of palmitoyl-coenzyme A and palmitoylcarnitine interaction with perdeuterated-chain phospholipid bilayers.

Mixtures of di-(perdeuteropalmitoyl)-sn-glycero-3 choline ([2H62]Pam2GroPCho) 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 degrees C; palmitoylcarnitine mixes with [2H62]Pam2GroPCho without perturbing the gel-fluid transition of the phospholipid even at [2H62]Pam2GroPCho/palmitoylcarnitine 1:2 molar ratios; and palmitoyl-CoA, however, at similar proportions, smears out the [2H62]Pam2GroPCho 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.