Some metabolic characteristics of brown fat, with particular reference to the mitochondria

Ultrastructural and Biochemical Changes in Brown Fat in Cold-Exposed Rats

“…Studies of the intracellular localization of various enzymes in the brown fat of the ground squirrel (27) have suggested that the distribution patterns are consistent with those established for heart and liver (2, 3) : cytochrome oxidase and succinate dehydrogenase are localized in the inner membranes of the mitochondria, aconitase is in the outer membranes, and malate dehydrogenase is partitioned between the mitochondria and the soluble phase . In rat brown fat, it was of interest to note that the activity of succinate dehydrogenase increased more extensively than that of cytochrome oxidase .…”

“…Preliminary experiments have shown that the increase in succinate dehydrogenase activity of homogenized brown fat during cold adaptation is paralleled by an increase in the activity of iso-3 3 0 THE JOURNAL OF CELL BIOLOGY VOLTJME 41, 1969 lated mitochondria . Otherwise, the biochemical and morphological features of brown fat from the 3-to 8-wk cold-adapted rat resemble those of ground squirrel axillary brown fat (27) . In general, it seems that the initial response of the mature brown fat cells to the cold is a combustion of their lipid and glycogen reserves, leading to a reduction in size of the fat droplets and glycogen deposits .…”

“…Lysosomelike granules were also found in mature cells (Fig . 5) ; we previously observed lysosomes in mitocondrial preparations from axillary brown fat of the ground squirrel (27) .…”

“…The methods used for enzyme assays were the same as those described elsewhere (27), except that succinate dehydrogenase was assayed polarographi-cally, with either cytochrome c or phenazine methosulfate (6) as the acceptor . Nucleic acids were separated according to the procedure of Munro and Fleck (17), with a few modifications : the initial centrifugation and washings in 0 .2 N HC1O4 for removal of the acid-soluble components were carried out at 50,000 rpm (Spinco rotor 50 Ti) for 20 min ; the phospholipids were removed before alkaline hydrolysis of RNA ; and DNA was measured spectrophotometrically at 260 mµ, since this technique gave results identical with those obtained with the diphenylamine procedure and was both easier and more precise, especially at low levels of DNA .…”

“…We have followed the changes, during exposure to cold, in the activities of four mitochondrialinked enzymes in rat brown fat, as well as the changes in concentration of nucleic acids, total nitrogen, and phospholipids . From a number of these animals we have also taken samples of brown at for electron microscopic examination in an attempt to correlate the biochemical and ultrastructural changes ; although the fine structure of brown fat from several species has been described by a number of authors (4,9,10,14,19,22,27), to our knowledge no one has systematically studied the ultrastructural responses of this tissue to cold exposure . Besides noting changes in brown fat cells during cold exposure, we attempted to clarify further the differences between brown and white fat cells, and to offer some evidence for changes in less differentiated cells that may relate to their conversion to brown fat cells .…”