CHARACTERIZATION OF MACROMOLECULE RESONANCES IN THE H-1-NMR SPECTRUM OF RAT-BRAIN

The H-1 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 H-1 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 H-1 NMR spectrum to specific amino acids. Fractionation of the dialyzed cytosol of rat brain by gel filtration yielded qualitatively similar H-1 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 H-1 NMR spectrum of normal brain tissue arise from cytosolic proteins.