Experimental evidence for the role of cross-relaxation in proton nuclear magnetic resonance spin lattice relaxation time measurements in proteins

Abstract

Proton nuclear magnetic resonance (NMR) spin lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements are presented for a number of proteins with molecular weights spanning the range of 6,500-150,000 daltons. These measurements provide experimental evidence for the role of cross-relaxation in 1H NMR T1 measurements in proteins. The relationship between these measurements and the theory recently presented by Kalk and Berendsen is discussed. The results indicate that cross-relaxation dominates the T1 measurements for the larger proteins, even at relatively low resonance frequencies such as 100 MHz.