Mitochondrial Protein Turnover Research Articles

Effect of administration of 2-methyl-4-dimethylaminoazobenzene on the half-lives of rat liver mitochondria and cytochrome oxidase

The turnover of total mitochondrial proteins and cytochrome oxidase in the livers of rats administered with 2-methyl-4-dimethylaminoazobenzene (2-Me-DAB) has been determined. The incorporation of [ 14C]bicarbonate revealed a half-life of 3.1 days in control and 6 to 9 days in azodye administered animals for whole mitochondrial proteins. The incorporation of [ 35S]methionine yielded t 1/2 values of 8.5 days and 15.4 days, respectively. The t 1/2 of cytochrome oxidase, 10.8 days for control and 19.3 days for 2-Me-DAB-treated animals, indicated that the delay in the decay of the enzyme was of the same order as that of whole mitochondria. Short term incorporation revealed that the administration of the azodye stimulated the synthesis of the enzyme. Mitochondria isolated from azodye-administered animals appeared less susceptible to lysosomal proteolysis. Also, azodye administration seemed to impair the ability of lysosomes to degrade mitochondria.

Adenosine 5'-triphosphate stimulates the release of polypeptides from mitochondria

There was release of polypeptides to the medium when mitochondria containing labeled proteins were incubated with a rat liver post-mitochondrial supernatant. The release of polypeptides increased with the amount of rat liver extract added. Addition of cycloheximide did not inhibit the effect. Heating the postmitochondrial supernatant did not inhibit the release of mitochondrial proteins, indicating that it was due to a heat-stable factor. The factor responsible has been isolated and identified as ATP. The presence of EDTA inhibits the release of polypeptides caused by ATP and Mg 2+ stimulates it. The possible role of ATP in the turnover of mitochondrial proteins is briefly discussed. Adenosine 5'-triphosphate Mitochondria Protein turnover

Regulation of Mitochondrial Protein Concentration: A Plausible Model Which May Permit Assessing Protein Turnover

Publisher Summary This chapter focuses on regulatory controls of mitochondrial protein turnover and measurement of mitochondrial protein degradation. Cell metabolism is mediated by the activity of many enzymes and is controlled by the regulation of key enzyme activities and enzyme levels. Most mitochondrial proteins are coded by nuclear genes and synthesized on cytosolic ribosomes as larger precursors, which then migrate and are imported into mitochondria. The overall protein concentration per cell volume changes very little, although the concentration of individual proteins may do so temporarily. Therefore, protein synthesis and degradation should be closely interrelated. The in vitro protein concentration in mitochondria may be regulated by the entry of mitochondrial protein precursors from the cytosol. Enzymes are flexible molecules whose conformations can be altered upon binding of substrates or other ligands. Mitochondrial proteins are degraded by lysosomes because mitochondria are frequently seen inside autophagic vacuoles. The importance of protein degradation is chiefly as a process to control the concentration of a protein and, thus, cell metabolism. Protein synthesis is usually controlled by regulating the amount of its messenger RNA available for translation.

Turnover of newly synthesized cytochromes P-450 scc and P-450 11 β and adrenodoxin in bovine adrenocortical cells in monolayer culture: Effect of adrenocorticotropin

The turnover of newly synthesized cytochromes P-450 scc and P450 11 β and adrenodoxin was investigated in bovine adrenocortical cells in primary monolayer cultures. Cells were pulse-radiolabeled with [ 35S]methionine, and specific newly synthesized enzymes were immunoisolated at various times following labeling and quantitated. Adrenocorticotropin (ACTH) treatment did not alter the average turnover rate of total cellular proteins or that of total mitochondrial proteins. The half-life of total cellular proteins of control and ACTH-treated cells was determined to be 20.5 and 23 h, respectively. The half-life of mitochondrial proteins of control and ACTH-treated cells was determined to be 42.5 and 44 h, respectively. The turnover rate of newly synthesized cytochrome P-450 scc was approximately the same as total mitochondrial protein ( t 1 2 = 38 h ), and was unchanged by ACTH treatment ( t 1 2 = 42 h ). ACTH treatment did not greatly alter the turnover rate of adrenodoxin. The half-life of adrenodoxin from control and ACTH-treated cells was determined to be 20 and 17 h, respectively. However, ACTH treatment appeared to increase the half-life of cytochrome P-450 11 β from 16 h in control cells to 24 h in treated cells. The differential rate of turnover of mitochondrial proteins studied here supports the contention that mitochondria are subject to heterogeneous degradation. It appears that chronic treatment of bovine adrenocortical cells in culture with ACTH leads to increased steroidogenic capacity, primarily as a result of increased synthesis of steroidogenic enzymes, although, as shown for cytochrome P-450 11 β ACTH action might also increase steroidogenic capacity by increasing the half-life of this steroid hydroxylase.

Effects of hypoxia and fasting on the cytochrome concentration in intestinal epithelial villous cell mitochondria. Role of changes in the life-span of the cells.

The effects of hypoxia in vivo (40.8 kPa barometric pressure up to 120 h) and fasting on the characteristics of intestinal epithelial villous cell mitochondria and the turnover of epithelial villous cells and mitochondria were studied in rats. Using cells and mitochondria isolated in the isotonic mannitol medium, it was found that 24-h hypoxia or fasting did not alter the mitochondrial cytochrome content, but 48-h hypoxia or fasting led to increases of 70% and 37% in the cytochrome aa3 concentration in the hypoxic and fasting animals respectively. The turnover of intestinal epithelial cells was studied by observing the labelling kinetics of the cells with 3H-thymidine and the turnover of the cell and mitochondrial proteins with (guanido-14C)-arginine or 3H-leucine. The decay in thymidine radioactivity obeyed exponential kinetics from which half-lives of 1.15, 1.31 and 1.53 days were calculated in the control, fasting and hypoxic animals respectively. The half-lives for total cellular protein were 1.31, 1.54 and 1.54 days respectively when calculated from the (guanido-14C)-arginine experiments, or 0.69, 0.75 and 0.99 days when calculated from the leucine experiments. The labelling experiments with (guanido-14C)-arginine indicated that the turnover of mitochondrial proteins in intestinal epithelial cells is the same as that of the cells themselves. Since the turnover of mitochondrial proteins in other tissues is shown to be a relatively slow process, the increase in the cytochrome concentration in the intestinal cells of the hypoxic rats must be due to the longer life of the cells, which allows for the synthesis of larger amounts of the mitochondrial components.

Turnover of Mitochondrial Proteins in Rat Liver

Conference Article| April 01 1979 Turnover of Mitochondrial Proteins in Rat Liver R. J. MAYER R. J. MAYER 1Department of Biochemistry, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1979) 7 (2): 306–310. https://doi.org/10.1042/bst0070306 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation R. J. MAYER; Turnover of Mitochondrial Proteins in Rat Liver. Biochem Soc Trans 1 April 1979; 7 (2): 306–310. doi: https://doi.org/10.1042/bst0070306 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1979 Biochemical Society1979 Article PDF first page preview Close Modal You do not currently have access to this content.

Effects of chronic ethanol consumption on the rate of rat liver mitochondrial protein turnover and synthesis

Incorporation in vitro of labeled leucine into isolated rat liver mitochondria was decreased in animals chronically fed ethanol. To avoid artifactual leucine incorporation, no trichloroacetic acid (TCA) precipitation was performed. Further, it was found that when these mitochondrial proteins were separated on sodium dodecyl sulfate polyacrylamide gels, no specific reduction of leucine incorporation into any individual protein bands could be detected. This probably reflected a general decrease in amino acid incorporation occurring in these isolated mitochondria. Incorporation in vivo of labeled arginine detected a decrease in the viability of rat liver mitochondria from chronic ethanol-fed rats. This incorporation revealed a 2-day decrease in the half-life of liver mitochondria from chronic ethanolfed rats. It was also found that arginine incorporation by the cytoplasmic protein-synthesizing system is increased in vivo after chronic ethanol feeding. The results from these experiments suggest that if this reaction were to persist through continuous consumption of ethanol, there would in time be diminished amounts of properly assembled proteins which are necessary for membrane structure and function. Whether or not such induced deficiencies in the mitochondria over a long period of time are precursors for alcoholic hepatitis and/or cirrhosis remains to be explained.

Regulation of mitochondrial membrane protein turnover by thyroid hormone(s).

Effects of thyroidectomy on turnover rate of proteins of rat liver mitochondria, mitochondrial membranes and microsomes were examined. Thyroidectomy resulted in a significant increase in the half-lives of whole mitochondria and inner membrane-matrix, the effect being less pronounced on the half-lives of outer mitochondrial membrane and microsomes.

Growth hormone and liver mitochondria effect on morphology and protein turnover

Electron micrographs of hepatocytes from hypophysectomized rats when compared with those of normal rats showed increased number or crowding of mitochondria per unit cytoplasmic volume with decreased endoplasmic reticulum, decreased mitochondrial matrix density, and the presence of partitioned mitochondria. After hypophysectomy, the recovery of mitochondrial proteins per gram of wet liver, by centrifugation, was increased. The mean half-life value for the turnover of total mitochondrial proteins was doubled when measured by injection of either l-[4,5- 3H]leucine or l-[guanidino- 14C]arginine. These changes were reversed towards normal by subsequent treatment with growth hormone. These and other results suggest a role for GH in the maintenance of a normal population of properly functioning mitochondria in liver.

Regulation of mitochondrial protein turnover by thyroid hormone(s)

1. The effect of thyroidectomy on turnover rates of liver, kidney and brain mitochondrial proteins was examined. 2. In the euthyroid state, liver and kidney mitochondria show a synchronous turnover with all protein components showing more or less identical half-lives compared with the whole mitochondria. The brain mitochondrial proteins show asynchronous turnover, the soluble proteins having shorter half-lives. 3. Mitochondrial DNA (m-DNA) of liver and kidney has half-lives comparable with that of whole mitochondria from these tissues. 4. Thyroidectomy results in increased half-lives of liver and kidney mitochondria, with no apparent change in the half-life of brain mitochondria. 5. A detailed investigation of the turnover rates of several protein components revealed a significant decrease in the turnover rates of mitochondrial insoluble proteins from the three tissues under study. 6. The turnover rates of m-DNA of liver and kidney show a parallel decrease. 7. Thus it is apparent that thyroid hormone(s) may have a regulatory role in maintaining the synchrony of turnover of liver and kidney mitochondria in the euthyroid state. Turnover of brain mitochondria may perhaps be regulated by some other factor(s) in addition to thyroid hormone(s). 8. It seems likely that during mitochondrial turnover m-DNA and insoluble proteins may constitute a major unit. 9. The mitochondrial protein contents of the three tissues are not affected by thyroidectomy. 10. No correlation was seen between the turnover rate of mitochondria and cathepsin activity in any of the tissues under study in normal or thyroidectomized animals. 11. On the other hand, mitochondrial proteinase activity shows good correlation with the turnover rates of mitochondria in normal animals, and a parallel decrease in activity comparable with the decreased rates of turnover is observed after thyroidectomy. 12. It is concluded that mitochondrial proteinase activity may play a significant role in their protein turnover.

Protein synthesis and turnover in normal and hypertrophied heart

This review deals with some aspects of the synthesis, assembly and turnover of mitochondrial and myofibrillar proteins in normal and hypertrophied hearts. The dynamic state of the myocardium, in which intracellular proteins and organelles are constantly being destroyed and synthesized, is emphasized. In normal cardiac muscle, mitochondrial inner membrane cytochromes turn over synchronously with half-lives of 5 to 6 days. The various myofibrillar proteins also turn over; the fact that they do so with identical apparent half-lives of 8 to 10 days suggests that these proteins are assembled and degraded synchronously. In cardiac hypertrophy produced by constriction of the ascending aorta in rats, inner mitochondrial membrane cytochromes increase in parallel. Early in hypertrophy (1 day after aortic constriction) cytochrome content per gram of heart weight increases, indicating a disproportionate increase in mitochondrial cytochrome mass. By the third postoperative day there already is a decrease in cytochrome content per gram of heart weight. The increase in mitochondrial cytochrome content observed in the hypertrophied heart appears to be due to a decreased rate of cytochrome destruction as well as to an increased rate of cytochrome synthesis. The data on myosin accumulation are consistent with either decreased destruction of myosin or increased efficiency of reutilization of labeled amino acids.

Lipid metabolism during cold-exposure and during cold-acclimation.

AbstractThe lipid‐containing tissues are important in cold‐exposure (exposure to cold of animals not previously living in the cold) and in cold‐acclimation (the adaptive state achieved when animals have lived in the cold for several weeks); these are the white adipose tissue and the brown adipose tissue. The white adipose tissue serves as a store of readily mobilized substrate (free fatty acids [FFA]) for calorigenesis in other tissues during cold‐exposure, principally for shivering thermogenesis in muscle. The mobilization of the sterol lipid is brought about through activation of the sympathetic nervous system by the cold stress. The brown adipose tissue has two functions in cold‐exposure and in cold‐adaptation, both quite distinct from the function of the white adipose tissue. These functions are heat production and the maintenance of the adaptationto cold. The triglycerides stored in the brown adipose tissue are mobilized as FFA, also via activation of the sympathetic nervous system, but the FFA are used primarily within the brown adipose tissue itself. The FFA are the agents which switch on the calorigenesis in the brown adipose tissue (via a poorly understood form of “loosening” of the coupling of oxidative phosphorylation); they also serve as the substrate for the calorigenesis. The heat‐producing function of the brown adipose tissue occurs in both cold‐exposed and in cold‐acclimated animals; it is of greater importance in the latter because this tissue normally grows in response to cold. Much of the heat production in cold‐acclimated animals (nonshivering thermogenesis) occurs outside the brown adipose tissue itself, most probably in the muscles, and the cold‐acclimated animal differs from the cold‐exposed animal in being able to switch on nonshivering thermogenesis via activation of the sympathetic nervous system. The maintenance of this adaptation for nonshivering thermogenesis in tissue other than the brown adipose tissue itself depends upon the brown adipose tissue. The adaptation disappears if the brown adipose tissue is removed; the adaptation does not develop if the normal proliferation of mitochondria in the growing brown adipose tissue is inhibited (with oxytetracycline) during acclimation of rats to cold. The mechanism by which the brown adipose tissue exerts this second function is at present unknown. An increased turnover of certain mitochondrial proteins occurs in those tissues (skeletal muscle and brown adipose tissue) in which nonshivering thermogenesis occurs in cold‐acclimated rats; no change in turnover of mitochondrial proteins occurs in other tissues (liver and kidney). The relation of this alteration in mitochondrial proteins to the adaptation for nonshivering thermogenesis is at present unknown. However this first demonstration of a biochemical difference between skeletal muscle of cold‐acclimated rats and skeletal muscle of warm‐acclimated rats opens up a new approach to the study of the nature of both the adaptation for nonshivering thermogenesis and of the role of the brown adipose tissue in the development and maintenance of this adaptation.

Rates of recovery of irreversibly inhibited monoamine oxidases: a measure of enzyme protein turnover.

1. After irreversible inhibition of monoamine oxidase (MAO) in rats with hydrazine derivatives (3-amino-2-oxazolidinone, furazolidone, benmoxine) and the non-hydrazine pargyline, recovery of enzyme activity occurred at rates which were characteristic for the organ investigated and independent of the chemical structure of the irreversible inhibitor. The respective half times were the same in homogenates and in mitochondria and amounted to about 10 days in the brain and 3 to 4 days in the liver; in the small intestine, mucosal MAO activity recovered with a half time of 0.5 days, whereas in the residual intestinal layers a half time of about 4 days was found.\3-Tranylcypromine is not an irreversible inhibitor: the half times of MAO recovery were 3.6 days in the brain and 2.4 days in the liver. Thus, long duration of inhibition and organ-specific half times of recovery of MAO inhibition are characteristic features of irreversible inhibitors. 2. When mitochondrial protein was labelled by i.v. injection of 14C-leucine, specific radioactivity declined with a half time of 9.4 days in the brain and 4.0 days in the liver; for the intestinal mucosa and for the residual intestinal layers, a half time of 0.5 and 4.4 days, respectively, was found. As these values are nearly identical with those found for the rates of MAO recofery after irreversible inhibition, the assumption is supported that irreversibly inhibited MAO must be replaced by newly synthetized enzyme. Vice versa, the rates of MAO recovery after irreversible inhibition seem to reflect the rates of mitochondrial protein turnover. Measurements of the rate of recovery of irreversibly inhibited MAO activity may therefore be useful to determine the turnover of the enzyme protein.