The folding of apomyoglobin has received intense scrutiny. The protein is relatively simple, and it serves as an archetype for folding of proteins which are small, single-domain, and globular. The holoprotein contains 153 residues organized into eight strands of mostly a-helical segments, labeled A-H. Near neutral pH, apoMb adopts a structure that is native-like according to the available NMR, CD and calorimetric evidence. The relaxation kinetics of native-ApoMb in response to a T-jump are shown above. The solvated helical substructure exhibits a relaxation time typical of isolated helices (blue trace) such as the model peptide described previously. This is the case even though these helices may be in contact with each other, held together by loose hydrophobic forces. Thus, the a -helical secondary structures can be formed early on the folding pathway of apoMb, on the time scale of tens of nanoseconds. In contrast, the relaxation time observed for the native helices of ApoMb-N (monitored at 1650 cm^-1) is some three orders of magnitude slower (green trace), analogous to the relaxation rate of the coiled-coil structure of GCN4-p1 (green trace). This slower relaxation is not limited by the intrinsic helix formation rate, but rather reflects the slower rates of the melting and formation of helix-helix and sidechain packing interactions.