The backbone dynamics of the major coat protein (gVIIIp) of the filamentous bacteriophage M13, solubilized in detergent micelles, have been studied using 15N nuclear magnetic resonance spectroscopy at three frequencies. Motional parameters and overall and internal correlation times were derived with the model-free approach. It was also checked whether these parameters had to be modified due to anisotropic motion of the protein/micelle complex. Reduced spectral density mapping was used to calculate the spectral densities at J(O), J(omegaN), and [J(omegaH)]. The spectral densities were interpreted by mapping a linear or scaled linear combination of two Lorentzians onto a J(O)-J(omega) plot. The major coat protein of bacteriophage M13 consists of two alpha-helices, one of which is hydrophobic and located within the micelle, while the other is amphipathic and located on the surface of the micelle. Our results indicate that the motion of the hydrophobic helix is restricted such that it corresponds to the overall tumbling of the protein/micelle complex. The interpretation of the relaxation data of the amphipathic helix by means of the model-free approach and the reduced spectral density mapping indicate that in addition to the overall motion all residues in this helix are subject to motion on the fast nanosecond and picosecond time scales. The motions of the vectors in the low nanosecond range are characterized by similar values of the spectral densities and correlation times and represent the motion of the amphipathic helix on and away from the surface of the micelle. The relaxation data of the residues in the hinge region connecting the helices show that there is an abrupt change from highly restricted to less restricted motion. Both the C-terminal and N-terminal residues are very mobile.