CROSS-POLARIZATION NMR OF N-15 LABELED SOYBEANS

Cross-polarization 15N nmr spectra of 15N-labeled soybean seeds, pods, and leaves have been obtained at 9.12 MHz both with and without high-speed sample rotation at the magic angle. Spectral resolution is sufficient to permit a determination of the relative concentrations of amide and amine nitrogens, as well as of a few specific amino acid residues of proteins in the solid, intact samples. Utilization by soybean of nitrogen from labeled fertilizer in the presence of dinitrogen fixation can be determined from these spectra. A double-cross polarization 13C nmr spectrum of a spinning, 15N-labeled seed has been obtained in which resonances are observed only from these carbons directly bonded to nitrogens. This technique leads to a qualitative estimate of amino-acid composition of the protein which is complementary to that obtained directly from the 15N nmr spectrum. © 1979.