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 cytoso l was investigated following centrifugation and dialysis to remove low molecular weight metabolites and peptides (<3500 daltons). At least s even 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 macromolecul e fraction coincided with those measured in a previous study of rat br ain tissue in vitro and in situ (K. L. Behar, T. Ogino, Magn. Reson. M ed. 17, 285 (1991)). Treatment of the cytosolic macromolecule fraction with a nonspecific protease permitted partial assignments of resonanc es in the H-1 NMR spectrum to specific amino acids. Fractionation of t he dialyzed cytosol of rat brain by gel filtration yielded qualitative ly similar H-1 NMR spectra for elution volumes corresponding to molecu lar masses from 12.5 kDa to over 100 kDa. The results indicate that ma ny of the background nonmetabolite resonances observed in the H-1 NMR spectrum of normal brain tissue arise from cytosolic proteins.