Estimation of protein turnover in soybean leaves using magic angle double cross-polarization nitrogen 15 nuclear magnetic resonance.

Magic angle cross-polarization 15N nuclear magnetic resonance spectra of intact lyophilized soybean leaves have been obtained at 9.12 MHz. The leaves were harvested over a 6-week period from 15N-uniformly labeled plants exposed to 13CO2 for 1 to 7 days. The concentration of 13C-15N double labels in the main chains of leaf protein was determined nondestructively by double cross-polarization techniques. Both incorporation and turnover rates of these double labels were estimated and together lead to the conclusion that the protein of a mature, fully expanded soybean leaf is fairly long lived, with a half-life of about 30 days.