The development of triple-resonance 3D and 4D heteronuclear NMR experiments applied on uniformly 15N/13C-labeled proteins has provided the tools to determine the solution structure of small and medium sized proteins up to 20-25 kDa. For systems larger than this, long molecular correlation times result in very efficient relaxation of the participating spins, especially 13C nuclei, attenuating signal intensity ans degrading spectral resolution.The use of full or partial deuteration has greatly facilitated the resonance assignment procedure of proteins uo to 40 kDa and protein in complexes as large as 60-70 kDa by NMR because of the better sensitivity and resolution achieved basically due to the smaller linewidths, better relaxation behavior and spectral simplification.
Excelent reviews have been published in 96STR1245 , 97COP722 , 94PROG371 , B99KRI27, and B99KRI75. Also see: