Asparagine amide metabolism in developing cotyledons of soybean

Magic-angle single and double cross-polarization (13)C and (15)N NMR spectra have been obtained of lyophilized soybean cotyledons cultured on media containing, as the only nitrogen source, [4-(13)C, amide-(15)N]asparagine. Single cross-polarization NMR shows directly and unambiguously that both labels from asparagine are incorporated extensively and nonrandomly into protein by the developing cotyledon during a 2-week period. A stable-isotope double label tags a chemical bond. The metabolic fate of the asparagine double label was followed by double cross-polarization NMR using the latter's sensitivity to the dipolar coupling between directly bonded (13)C and (15)N. These experiments show that in culture the direct incorporation of asparagine (with no scrambling of label) accounts for about half of all asparagine residues in soybean protein. This conclusion implies the operation of a regulatory apparatus in soybeans for both direct utilization and degradation of asparagine in protein synthesis.