Tissue fractionation studies. 12. Intracellular distribution of some dehydrogenases, alkaline deoxyribonuclease and iron in rat-liver tissue

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Abstract
The intracellular distribution of a number of components has been investigated in rat liver, according to a fractionation scheme in which the mitochondrial fraction is divided into two subtractions. In most experiments, cytochrome oxidase, acid phosphatase and glucose 6-phosphatase were measured as reference enzymes for mitochondria, lysosomes and microsomes respectively. Glutamic, malic and [beta]-hydroxybutyric dehydrogenases, together with alkaline deoxyribonuclease (DNase I), were found to be associated essentially with the true mitochondria. In addition, the microsomal fraction contained about 10% excess of alkaline deoxyribonuclease over what could be expected from mitochondrial contamination, and a similar excess of malic dehydrogenase was found in the final supernatant. As observed before, acid deoxyribonuclease (DNase II), which was measured here by an improved technique, showed a lysosomal distribution. About two-thirds of the easily detachable iron of liver tissue was recovered in the final supernatant. The remainder was distributed diffusely amongst all participate fractions, with a significant peak in the light mitochondrial fraction, which is richest in lysosomes. The iron content of this fraction was correlated with its acid phosphatase activity. These results support the contention, based on electron-microscope observations, that particles loaded with ferritin are concentrated together with lysosomes. After administration of iron, the iron content of all fractions was augmented; the greatest increase occurred in the nuclear and heavy mitochondrial fractions, in which the iron was probably present in the form of gross haemosiderin granules.