Electron Microscopy of Two Subcellular Fractions Isolated from Cerebral Cortex Homogenate

A considerable amount of information on tissue particulates has been obtained from combined biochemical and morphological investigations carried out mainly with liver and, to a lesser extent, with pancreas and muscle. There have been numerous biochemical studies with "mitochondrial fractions" isolated from 0.25 N sucrose homogenates of nervous tissue involving the oxidation of citric acid cycle intermediates (1-6), g]ycolysis (2, 4, 7), and oxidative phosphorylation (1, 3, 8-12). The criteria described by some of these authors (1, 12) for determining the purity of the fractions and the degree of preservation of the particulates are not completely satisfactory, being based on the low resolution of light or phase contrast microscopy. A recent publication from this laboratory described a study of D P N H 1 oxidation in rat cerebral cortex (13). To define in greater detail the intracellular distribution of the enzyme systems catalyzing this reaction it was found convenient to fractionate the 0.88 M sucrose homogenate into seven separate fractions. I t was found that the pat tern of distribution of the antimycin A sensitive pathway of D P N H oxidation corresponded to that accepted for enzymes held to be associated with mitochondria in other tissues, namely succinatecytochrome c reductase and cytochrome e oxidase. On the other hand, the distribution of the antimycin A insensitive pathway of D P N H oxidation was found somewhat similar to that of enzymes which have been considered to be associated with microsomal fractions; i.e., esterase and 5t-AMPase. Since the patterns found were roughly similar to those observed with liver (14) and since previous workers have reported on biochemical properties of subcellular fractions isolated from brain (1-12), it was of interest to examine the morphological appearance of these fractions. Fractions 3 and 7 were selected for initial morphological study because, as in the case of liver (14), they possessed enzymic