Morphology and Atp-Ase of Isolated Mitochondria

Abstract

Recent studies of the ATP-asO of mitochondria isolated from rat liver have shown that this enzyme is latent (1-5). Thus it does not exhibit full activity unless dinitrophenol (DNP) is present (1,3,5,6), or the preparation is aged at 37°C. (1-3), or frozen and thawed (4, 7). The mitochondrla used in most studies have been isolated in 0.25 M sucrose solutions (8). Such preparations differ in morphology from the mitochondria in situ. The former are spherical and appear to be swollen, whereas the latter are rod-or oval-shaped (9). Rod-shaped mitochondrla can be isolated in 0.88 M sucrose (9) and have been found to possess much higher ATP-ase activity (10, 11) than the round type (1-5).In view of these differences in enzymatic activity between the rod-and the round-shaped mitochondrla, the possibility arises that the observed properties of mitochondria isolated in 0.25 x¢ sucrose may be artifacts of preparation which may be correlated with changes in morphology upon isolation. This point becomes even more significant when it is realized that the round swollen mitochondria have been successfully used in the study of oxidative phosphorylation because of the very fact that their ATP-ase is latent thus permitting the measurement of maximal P/O ratios (1,(12)(13)(14). Although preliminary experiments indicate that the ATP-ase activity of mitochondria in 0.88 M sucrose may sometimes be increased by freezing and thawing (12) there are no reports of detailed experiments showing that this enzyme is latent in this preparation. Finally, the properties of the A'l~P-ase of mitochondria isolated in solutions of sucrose concentration other than 0:88 ~ or 0.25 x~ have not been investigated.An attempt has been made, therefore, to correlate changes in morphology of mitochondrla brought about by different methods of isolation with character-

A Case of Severe Hypermetabolism of Nonthyroid Origin With a Defect in the Maintenance of Mitochondrial Respiratory Control: A Correlated Clinical, Biochemical, and Morphological Study

“…The striking features of these changes were an enormous enlargement of the mitochondria in certain regions of the skeletal muscle, as well as a pronounced abundance of cristae in these mitochondria. It should be pointed out that although characteristic structural changes can be induced in liver mitochondria by various agents both in vitro (92)(93)(94) and in vivo (95)(96)(97), these changes are very different from those found here; they consist of a swelling of the mitochondrial body, connected with an uptake of water and characterized by a decrease rather than an increase in the tightness of the cristae. The morphologically abnormal mitochondria of the patient rather resemble mitochondria from tissues with very high metabolic activity.…”

Effect of Gamma Irradiation on the Desoxyribonuclease Ii Activity of Isolated Mitochondria

“…It has been shown by Witter el a/. (8) that such mitochondria do not resemble mitochondria in situ as closely as do mitochondria isolated in the medium used in the present study. The assay methods are such that Schneider and Hogeboom, by adding magnesium sulfate to their reaction mixture, measured a combination of both DNase I and II, while in the present study the use of versene insured the measurement of only DNase II.…”

Morphological and Functional Abnormalities in Mitochondria Associated with Synaptic Degeneration in Prion Disease

“…18 Ultrastructural integrity is a key indicator of mitochondrial function 24 and mitochondrial swelling, generally reflected by an increase of the mitochondrial area is a well-accepted hallmark of dysfunction of this organelle. 8,25 The mitochondrial area of at least 100 neuronal mitochondria from the stratum radiatum (minimum n ϭ 3 animal/time point) was measured. To achieve the best representation possible, the same animals and sections were used as in density analysis described above.…”