In parallel, Tycko and co-workers have also performed MAS
NMR studies of CA tubular assemblies. In their early work, they
have concluded on the basis of the various MAS NMR spectra of
1,3-13C-glycerol-labeled CA samples that CTD and NTD of CA are
largely rigid and retain their general secondary and tertiary structure
upon formation of tubes [18]. Using double quantum filtering
for further spectral simplification, they were able to assign 111
cross peaks by comparison with solution NMR chemical shifts.
INEPT and NOE-INEPT measurements also indicated that very
few CA residues are mobile.