Multidimensional 1H, 13C and 15N nuclear magnetic resonance spectroscopy has been used to study the complex between palmitoyl-coenzyme A and acyl-coenzyme A binding protein. The 1H and the 15N spectra of the holo-protein have been almost completely assigned and so has most of the 1H spectrum of the coenzyme A part of the protein-bound ligand. The palmitoyl part of the ligand has been uniformly labelled with 13C and the nuclear magnetic resonance signals of the carbon atoms and their protons have been assigned at the two ends of the hydrocarbon chain. A total of 1251 distance restraints from nuclear Overhauser effects and 131 dihedral angle restraints from three-bond coupling constants provided the basis for the structure calculation. A comparison of 20 structures calculated from these data to the average structure showed that they could be aligned with an atomic root-mean-square deviation of 1.3(+/- 0.2) A for all C, N, O, P and S atoms in protein and ligand. The apo-protein is a four-helix protein and this structure is maintained in the holo-protein. The four alpha-helices are Ac1 of residues 3 to 15, Ac2 from residue 20 to 36, Ac3 from 51 to 62, and Ac4 from 65 to 84. For the four alpha-helices of the peptide backbone of the holo-protein the root-mean-square deviation for the C, C alpha and N atoms was 0.42(+/- 0.08) A. The binding site for the palmitoyl-chain stretches between the N-terminal end of Ac3 where the carboxyl part binds, to the N-terminal of Ac3 where the omega-end of the palmitoyl part binds. The adenosine-3'-phosphate is bound near residues of each of the four helices in an arrangement where it can form salt bridges and/or hydrogen bonds to either backbone or side-chain atoms of Ala9, Tyr28, Lys32, Lys54 and Tyr73. The polar parts of the pantetheine and the pyrophosphate are structured in the bound ligand to form an interface with the solvent. Also the ligand forms a set of non-polar intramolecular interactions where the adenine, the pantetheine, and the palmitoyl-chain are associated, so overall the structure of the bound ligand seems to be organized to protect the lipophilic palmitoyl part from the polar solvent.