Tissue fractionation studies. 13. Analysis of mitochondrial fractions from rat liver by density-gradient centrifuging

Abstract

I959 2. Glutamic, malic and f-hydroxybutyric de- hydrogenases, together with alkaline deoxyribo- nuclease (DNase I), were found to be associated essentially with the true mitochondria.In addi- tion, 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.3.About two-thirds of the easily detachable iron of liver tissue was recovered in the final super- natant.The remainder was distributed diffusely amongst all particulate 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.4. After administration of iron, the iron content of all fractions was augmented; the greatest in- crease occurred in the nuclear and heavy mitochondrial fractions, in which the iron was probably present in the form of gross haemosiderin granules.