Quantitative analysis of ¹H NMR detected proteins in the rat cerebral cortex <i>in vivo</i> and <i>in vitro</i>

Data show that the macromolecular peaks in the brain at TE>100 ms arise predominantly from proteins which are acid soluble, and the assignment of macromolescular signals in the cerebral spectrum to a given polypeptide is discussed in the light of protein analyses of brain acid extracts.

Abstract

Spectral editing experiments were used to quantify CH3 groups from macromolecular species in the chemical shift region from 1.2 to 1.4 ppm of rat cerebrum in vivo. Two peaks centred at 1.22 and 1.40 ppm were revealed when irradiation was positioned at 4.35 or 4.30 ppm. These peaks had lower saturation factors (1 vs. 1.72 +/- 0.10) than N-acetyl aspartate (NAA) and shorter T2 [60 +/- 5.8 (1.22 ppm) and 51 +/- 2.2 (1.40 ppm) vs. 123 +/- 12 (NAA) ms]. The concentrations of the peaks at 1.22 and 1.40 ppm were calculated to be 0.65 +/- 0.09 and 1.37 +/- 0.18 mmol of CH3 equivalents/kg brain. Acid extract from cerebral cortices contained macromolecular peaks at the same chemical shifts with approximately the same area ratios to NAA as in vivo. These data show that the macromolecular peaks in the brain at TE > 100 ms arise predominantly from proteins which are acid soluble. The assignment of macromolecular signals in the cerebral spectrum to a given polypeptide (thymosin beta 4 and histone H1) is discussed in the light of protein analyses of brain acid extracts.