Larmor frequency selective model free analysis of protein NMR relaxation

The Lipari-Szabo dynamical formalism is extended by setting the time constants of the Lorentzian terms to [Formula: see text] and [Formula: see text]. This analysis is compared to the earlier proposed three-parameter [Formula: see text] extended model free formalism with regard to the range of equivalence and the advantages of the simplified two-parameter (S (inff) (sup2) ,S (infH) (sup2) ) and (S (inff) (sup2) ,S (infN) (sup2) ) representations. Spectral density components are calculated and compared to those obtained from the spectral density analysis formalism. Protein relaxation data, commonly analyzed in terms of the two-parameter [Formula: see text] representation, may correspond to a dynamically heterogeneous behaviour that is more appropriately represented in terms of a fast limit order parameter and a second, lower frequency order parameter.