The preparation of rat‐liver mitochondria by conventional differential centrifugation and by zonal Centrifugation, after various disruption procedures: A comparative study

Rat liver was subjected to three different, disruption procedures (homogenization, explosive decompression, and Chaikoff press) and mitochondria were subsequently isolated by conventional differential Centrifugation and by zonal Centrifugation. The properties of these mitochondria were investigated by polarographic measurement of oxygen uptake and they were examined by electron microscopy. All three methods of disruption gave mitochondria which showed respiratory control. Nitrogen cavitation gave the most reproducible conditions for cell breakage and zonal Centrifugation gave good separation of subcellular organdies in extracts produced by this method. Some separation of the heterogenous mitochondrial populations was achieved by zonal Centrifugation

On the Size of the DNA in the Mammalian Chromosome: Structural Subunits

Alkaline degradation of mammalian DNA indicates that the molecule exists in the chromosome as an array of structural subunits. The size of the subunit of single-stranded DNA is circa 5 × 10(8) daltons, and it is of sufficient length to contain a number of synthetic units, replicons. The upper size limit of the multicomponent structure is in excess of 10(10) daltons. Mammalian cells of three different origins have been shown to contain the same basic structural DNA components and these components exist throughout the cell cycle. The nature of the links between the subunits is not known