Measurement of Relaxation-Rate Constants Using Constant-Time Accordion NMR Spectroscopy

Abstract

A pulse sequence is described for measurements of nuclear magnetic spin relaxation that incorporates elements of both accordion and constant-time NMR spectroscopy. Accordion spectroscopy reduces the dimensionality of the relaxation experiment from three to two by encoding the relaxation decay functions into the t1 interferograms; as a result, relaxation-rate constants can be measured in 1/2 to 1/3 the experimental acquisition time required for techniques in which a time series of two-dimensional spectra is recorded. Two novel methods are introduced for extracting relaxation-rate constants from t1 interferograms. Both methods utilize the different functional forms of the signal obtained by either incrementing or decrementing the accordion period synchronously with the t1 evolution period. The accuracy and precision of the constant-time accordion pulse sequence is verified by determining the 15N spin-lattice relaxation-rate constants of Ca2+-loaded P43G calbindin D9k. The rate constants obtained in 11 hours using the constant-time accordion pulse sequence are statistically indistinguishable from results previously obtained in 38 hours using the conventional experimental protocol (J. Kördel, N. J. Skelton, M. Akke, A. G. Palmer, and W. J. Chazin, Biochemistry 31, 4856, 1992). © 1994 by Academic Press, Inc.