Characterization of macromolecule resonances in the 1H NMR spectrum of rat brain

The 1H NMR spectrum of the macromolecule fraction of rat brain cytosol was investigated following centrifugation and dialysis to remove low molecular weight metabolites and peptides (< 3500 daltons). At least seven well resolved resonances were detected between 0.9 and 3.0 ppm in the 1H NMR spectrum of rat brain cytosol after dialysis, several of which cannot be observed in vivo due to overlap with N-acetylaspartate, glutamate, glutamine, creatine, and gamma-aminobutyric acid. Several cross-peaks detected in 2D COSY spectra of the cytosolic macromolecule fraction coincided with those measured in a previous study of rat brain tissue in vitro and in situ (K. L. Behar, T. Ogino, Magn. Reson. Med. 17, 285 (1991)). Treatment of the cytosolic macromolecule fraction with a nonspecific protease permitted partial assignments of resonances in the 1H NMR spectrum to specific amino acids. Fractionation of the dialyzed cytosol of rat brain by gel filtration yielded qualitatively similar 1H NMR spectra for elution volumes corresponding to molecular masses from 12.5 kDa to over 100 kDa. The results indicate that many of the background nonmetabolite resonances observed in the 1H NMR spectrum of normal brain tissue arise from cytosolic proteins.