Abstract
Summary
1. The cytoplasm of liver has been fractionated by centrifugation in sucrose solution into microsomes, an upper pink mitochondrial layer and a lower normal, yellow mitochondrial layer. These fractions have been studied with respect to amino acid incorporation, cholesterol formation and the ratio of nucleic to protein radioactivity. The mitochondria-P differed sufficiently in these properties from the normal microsomes and mitochondria to be considered a distinct type of cytoplasmic particle. 2. The curve of the ratios of the lower, normal mitochondria to that of the top layer was found to parallel the weight curve of the rat upon aging. The total amount of mitochondria per unit weight of liver remained fairly constant, with the lower fraction increasing and the upper decreasing with age.
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