| abstract |
A phenylalanine labeled with a stable isotope, wherein a carbon atom bonded to an amino acid residue in a phenyl group is 13C, two to four carbon atoms of the residual five carbon atoms constituting said phenyl group are 12C atoms, to which deuterium atoms are bonded, and the further residual carbon atoms are 13C atoms, to which hydrogen atoms are bonded; a tyrosine labeled with a stable isotope, wherein a carbon atom bonded to an amino acid residue in a phenyl group is 13C, a carbon atom bonded to a hydroxyl group (an OH group) in a phenyl group is 12C or 13C, two to four carbon atoms of the residual four carbon atoms constituting said phenyl group are 12C atoms, to which deuterium atoms are bonded, and the further residual carbon atoms are 13C atoms, to which hydrogen atoms are bonded; or the like. The above amino acid labeled with a stable isotope allows the resolution of the complexity of aromatic ring NMR signals, which is the greatest reason for difficulties of NMR analysis in the case of a uniformly labeled amino acid residue having been used conventionally, and thus can markedly improve the sensitivity of the analysis. |