Interactions of oleoyl- and
octanoyl-coenzyme A (
CoA) with
phosphatidylcholine (PC) vesicles and
bovine serum albumin (BSA) were investigated by NMR spectroscopy. Binding of
acyl-CoA to small unilamellar PC vesicles and to BSA was detected by changes in 13C and 31P chemical shifts relative to the chemical shifts for aqueous
acyl-CoA. When
oleoyl-CoA (less than or equal to 15 mol %) was added to preformed vesicles, the 13C thioester signal (200.1 ppm) was upfield from the signal for micellar
oleoyl-CoA (201.7 ppm), suggesting decreased H-bonding (partial
dehydration) at the carbonyl group upon binding to the bilayer. When vesicles were prepared by cosonication of
oleoyl-CoA and PC, a second peak (199.8 ppm) was seen. The major peak at 200.1 ppm broadened and shifted after addition of Dy(NO3)3 and was not seen after addition of BSA, while the peak at 199.8 ppm was unaffected by either perturbation. Thus,
oleoyl-CoA in each bilayer leaflet was distinguished, and transbilayer movement was shown to be slow (t 1/2 greater than or equal to hours). PC vesicles remained intact with less than or equal to 15 mol %
oleoyl-CoA, while higher
oleoyl-CoA proportions produced mixed
micelles. In contrast, 13C spectra revealed rapid exchange (ms) of
octanoyl-CoA between the aqueous phase and PC vesicles and a low affinity for the bilayer. Thus, the binding affinity of
acyl-CoA for PC bilayers is dependent on the acyl chain length.
Oleoyl-CoA in the presence of BSA (1 mol/mol) gave rise to three carbonyl signals at 197.2-203.6 ppm. With 2-5 mol of
oleoyl-CoA/BSA, 1-2 additional signals were observed. None of the signals corresponded to unbound
oleoyl-CoA. Addition of [13C]carboxyl-enriched
oleic acid to
oleoyl-CoA/BSA mixtures revealed simultaneous binding of
oleic acid and
oleoyl-CoA to BSA, with some perturbation of binding interactions. Thus, BSA contains multiple binding sites for
oleoyl-CoA and can bind
fatty acid and
acyl-CoA simultaneously.