QUAKING MOUSE MYELIN: BIOCHEMICAL CHARACTERIZATION OF ZONAL GRADIENT SUBFRACTIONS

Abstract

AbstractThe brains of Quaking and littermate control mice were fractionated by differential and density gradient centrifugation into soluble, microsomal, myelin and related (SN 4) fractions. There were no apparent differences in protein composition between any Quaking and control fraction with the exception of myelin and SN 4. Analysis of CNP activity indicated that in Quaking animals a high proportion of the total activity was localized in microsomal fractions, while in controls a large percentage of activity was found in myelin and SN4; in contrast, there were no marhcd differences in the distribution of AChE activity between Quaking and control fractions.The yield of myelin isolated from Quaking animals was 3.6%, of that from controls by electron microscopy myelin fractions from both Quaking and controls consisted of compact myelin whorls. Zonal centrifugation on continuous sucrose gradients demonstrated that both control and Quaking myelin was distributed in a bell‐shaped mode with peak densities at 0.66 0.68 and 0.71‐0.75 M‐sucrose, respectively. The specific activity of CNP was generally lower in mutant subfractions than in controls. Protein analysis revealed that there were similar qualitative trends between light and heay myelin subfractions from both mutant and control animals, although the levels of proteolipid and small basic proteins were substantially lower in all Quaking fractions. These results indicate that. although all mutant myelin subfractions are compositionally abnormal, the type of particle heterogeneity in Quaking myelin is similar to that observed in controls.