THE INFLUENCE OF PRECURSOR POOL SIZE ON MITOCHONDRIAL COMPOSITION IN NEUROSPORA CRASSA

FORMATION OF MITOCHONDRIA IN NEUROSPORA CRASSA. A STUDY BASED ON MITOCHONDRIAL DENSITY CHANGES

The choline concentration used in the growth medium influences the density of mitochondria produced by the chol-1 mutant of Neurospora. Isopycnic centrifugation in sucrose gradients can be used to determine the density of mitochondria, and can resolve into two populations, mitochondria derived from a mixture of cells grown at low (1 microg/ml choline chloride) and high (10 microg/ml choline chloride) choline levels. In an experiment in which cells are shifted from low to high choline growth conditions, mitochondria obtained after varying time periods show a gradual decrease in density tending toward the level typical of high choline mitochondria. Over a 90-minute period of observation, during which time there is an increase of mitochondrial protein mass of approximately 50 per cent over that initially present, the mitochondria change density as a single population. These results are consistent with the view that mitochondria grow by random accretion of new lecithin into existing mitochondrial structures, and also that the mitochondrial population increases by division.

The oxidation of external NADH by an intermembrane electron transfer in mitochondria from the ubiquinone-deficient mutant E3-24 of Saccharomyces cerevisiae

Cells of the E3-24 mutant of the strain D273-10B of Saccharomyces cerevisiae, grown in a fermentable substrate not showing catabolite repression of respiration (2% galactose), are able to respire, in spite of their ubiquinone deficiency in mitochondrial membranes. Mitochondria isolated from these mutant cells oxidize exogenous NADH through a pathway insensitive to antimycin A but inhibited by cyanide. Addition of methanolic solutions of ubiquinone homologs stimulates the oxidation rate and restores antimycin A sensitivity in both isolated mitochondria and whole cells. Mersalyl preincubation of isolated mitochondria inhibits both NADH oxidation and NADH-cytochrome c oxido-reductase activity (assayed in the presence of cyanide) with the same pattern. Electrons resulting from the oxidation of exogenous NADH reduce both cytochrome b5 and endogenous cytochrome c. The increase in ionic strength stimulates NADH oxidation, which is also coupled to the ATP synthesis with an ATP/O ratio similar to that obtained with ascorbate plus N,N,N',N'-tetramethyl-p-phenylendiamine (TMPD) as substrate. The effect of cyanide on these activities and on NADH-induced endogenous cytochrome c reduction is also comparable. These results support the existence in vivo and in isolated mitochondria of a energy-conserving pathway for the oxidation of cytoplasmatic NADH not related to the dehydrogenases of the inner membrane, the ubiquinone, and the b-c1 complex, but involving a cytochrome c shuttle between the NADH-cytochrome c reductase of the outer membrane and cytochrome oxidase in the inner membrane.

Hypoxic coordinate regulation of mitochondrial enzymes in mammalian cells

The effect of hypoxic exposure on various mitochondrial enzymes and on cell mitochondrial genomic content was studied in two types of mammalian cells. Hypoxia depressed the activity of six enzymes to the same degree. The kinetics of depression and of recovery during reexposure to normoxia were statistically similar for three marker enzymes. Despite the global and symmetrical decrease in enzyme activities, mitochondrial DNA remained constant. This suggests either symmetrical loss of mitochondrial enzymes from all mitochondria or complete loss of enzymes from a subpopulation of mitochondria with retention of an intact mitochondrial genome.

Nuclear mutants of Neurospora crassa temperature-sensitive for the synthesis of cytochrome aa3. Mitochondrial protein synthesis and analysis of the polypeptide composition of cytochrome c oxidase

Three previously isolated mutants of Neurospora crassa, temperature-sensitive for the production of cytochrome aa3, have been further analyzed. These mutants have a slightly reduced capacity for mitochondrial protein synthesis when grown at 41 degrees C, although this relative deficiency appeared to be no greater than the deficiency in other cytochrome-aa3-deficient mutants. Thermolability studies revealed that the cytochrome c oxidase purified from each of the mutants grown at 23 degrees C is no more sensitive to heat inactivation than the enzyme isolated from wild-type cells. Sodium dodecylsulfate gel electrophoresis of immunoprecipitates obtained from the mitochondria of each of the mutants grown at 23 degrees C, using antiserum directed against holocytochrome c oxidase, indicated that all the subunits of cytochrome c oxidase were present in relative amounts similar to those found in mitochondria from wild-type cultures. However, when the mitochondria from mutant cultures grown at 41 degrees C were examined in the above fashion, only subunits 5 and 6 of the oxidase were detected. Nonetheless, the mitochondrially synthesized subunit 1, 2 and 3 polypeptides could be immunoprecipitated from mitochondria isolated from mutant cells grown at 41 degrees C and labelled with [3H]leucine in medium containing cycloheximide. Although subunits 4 and 7 could not be detected, because a suitable antibody was not available, the fact that five of the seven subunits were present, but not associated with each other, suggested that the genetic defects in these mutants may affect the process of cytochrome c oxidase assembly.

Mitochondrial adenosine triphosphatase of wild-type and poky Neurospora crassa

We have compared the adenosine triphosphatase (ATPase) activity of mitochondria prepared from wild-type Neurospora crassa and from poky, a maternally inherited mutant known to possess defective mitochondrial ribosomes and reduced amounts of cytochromes aa3 and b. poky contains two distinct forms of mitochondrial ATPase. The first is normal in its Km for ATP, specificity for nucleotides and divalent cations, pH optimum, cold stability, and sensitivity to inhibitors (oligomycin, N,N-dicyclohexyl carbodiimide, and adenylyl imidodiphosphate). The fact that membrane-bound, cold-stable, oligomycin-sensitive ATPase activity is present in poky (with an activity of 1.93 +/- 0.03 mumol/min-mg of protein compared with 1.33 +/- 0.07 mumol/min-mg of protein in the wild-type strain) and also in chloramphenicol-grown wild-type cells suggests that products of mitochondrial protein synthesis play only a limited role in the attachment of the mitochondrial ATPase to the membrane in Neurospora. poky also contains a second form of mitochondrial ATPase, which has an activity of 1.5 +/- 0.2 mumol/min-mg of protein, is oligomycin sensitive but cold labile, and presumably is attached less firmly to the mitochondrial membrane. The two forms, added together, represent a substantial overproduction of mitochondrial ATPase by poky.

Cyanide-resistant respiration of a Neurospora crassa membrane mutant

Choline starvation of the Neurospora crassa chol-1 mutant leads to a decrease in respiration through the cytochrome chain and a concomitant induction of the alternate oxidase.

Mitochorial form in hepatic parenchymal cells in rats of several ages

Slices of livers from neonatal, 7-day-old and adult rats were fixed in osmium tetroxide or a formaldehyde-osmium tetroxide sequence and processed for electron microscopy. Mitochondria from neonatal hepatic parenchymal cells are pleomorphic. Disc-shaped forms are common. In 7-day-old animals, cylinders are the most numerous single form, discs are present but smaller, and spherical forms increase in number. In the adult, mitochondria are predominantly cylindrical in form. The average volume of neonatal mitochondria is greater than that of 7-day-old or adult mitochondria.

Mitochondrial changes in flight muscles of normal and flightless Drosophila melanogaster with age

Fine structural changes in mitochondrial morphology pertaining to size, number and growth were examined in flight muscles of normal and experimentally dewinged male Drosophila melanogaster ranging up to 26 days of age. In the normal winged flies, the number of mitochondria decreases during the first week of adult life whereas the size of individual mitochondrial profile increases significantly. Changes in mitochondrial size and number are due to the fusion of mitochondria. Fused mitochondria are are extremely large in size and irregular in shape. In 26-day old normal flies, the number of mitochondria increases while the mitochondrial size is recuced indicating mitochondrial division. In comparison to the normal flies, dewinged flies exhibit a similar degree of mitochondrial fusion and growth during the first week of life. However, the extent of mitochondrial fission in 26-day old dewinged flies is greater than in the normal flies of this age. Structural mechanisms of mitochondrial fusion and fission are described. The objective of this study was to examine the relative effects of age and flight activity on the mitochondria.

Effects of thiamine deprivation and replacement on the mitochondrion of Polytomella agilis

Late log-phase cells of Polytomella agilis, grown with or without thiamine, were examined by electron microscopy. The mitochondrial profiles of cells cultivated in the presence of thiamine are relatively few in number and irregular in shape. The inner membranes, randomly dispersed in a light matrix, are elongated, vesicular, or branched in appearance. In vitamin-deficient cells, numerous mitochondrial profiles are evident. They have a regular circular or ovoid appearance. The inner membranes are regularly arrayed in an electron-dense matrix and generally appear elongated. By means of partial 3-dimensional reconstruction of whole cells the appearance of mitochondrial profiles in vitamin-deficient cells can be explained by the increased branching of a single structure. Following transfer of vitamin-deficient cells to complete medium, normal mitochondrial structure is attained by similar to 3 hr. Reduced-minus-oxidized difference spectra of suspensions of normal and vitamin-deficient cells, grown with gentle aeration, were recorded. The concentrations of a- and b-type cytochromes are reduced by 80-90 per cent, and c-type cytochromes are reduced by 40 per cent in thiamine-deficient cells.

Mechanism of the formation of megamitochondria induced by copper-chelating agents. I. On the formation process of megamitochondria in cuprizone-treated mouse liver

Processes of the formation of cuprizone-induced megamitochondria in mouse liver have been studied in detail by electron microscopy. The earliest change observed was the presence of large intramitochondrial granules. The next stage was the formation of myelin figures by which mitochondria were apparently connected. The third stage was characterized by megamitochondria connected with each other by their outer membranes. Continuity of mitochondria were further examined by serial sections, and megamitochondria were proved to be connected to each other far more frequentlythan expected on one plane of section. A model for the mechanism of megamitochondrial formation is proposed based on electron microscopic evidences, involving the fusion of mitochondrial membranes. Possibility is also discussed that cuprizone-induced megamitochondria may fuse to one single branching mitochondrion.

Cobalt as a mitochondrial density marker in a study of cytoplasmic exchange during mating of Schizophyllum commune

A slow in vivo uptake of cobalt from a growth medium resulted in an increase in density of mitochondria of Schizophyllum commune. Differential labeling of donor and resident mycelia, and subsequent analysis of resident mycelia surrounding donor implants, detected cobalt-dense mitochondria and demonstrated exchange of mitochondria after hyphal fusion. Transfer of mitochondria occurred in fully compatible, common-A, and common-AB matings, but was not detected in common-B matings of the tetrapolar Basidiomycete S. commune.

Rapid lateral diffusion of phospholipids in rabbit sarcoplasmic reticulum

Phospholipid spin labels incorporated in the sarcoplasmic reticulum from rabbit-skeletal muscle undergo rapid lateral diffusion within the plane of the membrane. The diffusion constant, D, is 6x10(-8) cm(2)/sec at 37 degrees . With this diffusion constant, a phospholipid molecule can diffuse a distance of the order of 5000 nm in 1 sec.

Growth and differentiation of mitochondria in the regenerating rat adrenal cortex

Diameters of the circular profiles of spherical mitochondria in parenchymal cells of the zona fasciculata in rat adrenal cortex were measured for intact controls and for the regenerating adrenal cortex on electron micrographs recorded at random. The diameter data were then processed by Bach's method which deals with the sphere size distribution. The structural parameters of the mitochondria were computed with the aid of an electronic computer. The total number of mitochondria in all the parenchymal cells of the zona fasciculata were calculated. The surface area of the inner mitochondrial membrane was then determined stereologically. Biochemical parameters were obtained for the protein, the phospholipid, and the cytochrome P-450 content, per averaged mitochondrion. The number of cytochrome P-450 molecules contained in the inner membrane was determined in terms of the unit surface area and of the unit amount of phospholipid. These correlated biochemical and stereological parameters have led to the following conclusions. (a) The genesis of the mitochondria after the adrenal enucleation is almost completed within 10 days. (b) During the period of mitochondrial proliferation, the mitochondria are small in size and also immature both in the structure and in the function of their inner membrane, (c) These small and immature mitochondria grow through an increase of the phospholipid and protein, and this increase is accompanied by expansion of the area of the membrane surface, (d) An enrichment of the inner membrane with cytochrome P-450 molecules occurs, thus indicating the differentiation of adrenocortical mitochondria. The process of membrane differentiation is not tightly coupled with that of membrane growth.

Cyanide-resistant respiration in Neurospora crassa

Cell respiration in wild type and poky was studied as part of a long-term investigation of cyanide-resistant respiration in Neurospora. Respiration in wild type proceeds via a cytochrome chain which is similar to that of higher organisms; it is sensitive to antimycin A or cyanide. Poky, on the other hand, respires by means of two alternative oxidase systems. One of these is analogous to the wild-type cytochrome chain in that it can be inhibited by antimycin A or cyanide; this system accounts for as much as 15% of the respiration of poky f(-) and 34% of the respiration of poky f(+). The second oxidase system is unaffected by antimycin A or cyanide at concentrations which inhibit the cytochrome chain maximally. It can, however, be specifically inhibited by salicyl hydroxamic acid. The cyanide-resistant oxidase is not exclusive to poky, but is also present in small quantities in wild type grown under ordinary circumstances. These quantities may be greatly increased (as much as 20-fold) by growing wild type in the presence of antimycin A, cyanide, or chloramphenicol.

Euglena gracilis: formation of giant mitochondria

The addition of antimycin A (0.5 microgram per milliliter) to cultures of a bleached strain of Euglena gracilis in the logarithmic phase of growth on succinate as a carbon source results in (i) an interruption of growth for 24 hours and (ii) an increase in whole-cell respiration and the emergence of a novel succinoxidase activity within 2 to 4 hours. After 3 to 5 hours, the mitochondria enlarge, fuse, and form a sheathlike structure situated close to the periphery of the cell.

Changes in the proportions of two mitochondrial populations during the development of embryonic chick liver

1. Two populations of morphologically intact mitochondria were isolated from embryonic, neonatal and adult chick liver by isopycnic centrifugation. 2. The protein/phospholipid ratio of the total mitochondrial fraction, the low-density mitochondria (B2, d1.176) and the high-density mitochondria (B3, d1.206) did not differ significantly. 3. During development there is a marked increase in the B2 fraction in relation to the B3 fraction. 4. Cytochrome oxidase and malate dehydrogenase activities as well as respiratory control increased during the embryonic development of the chick, though their rates of increase were not correlated. 5. In the three different embryonic stages that were investigated, as well as in the neonatal and adult chick, the protein/lipid as well as the protein/phospholipid ratio stayed constant and showed no progressive increase, as had been previously reported. 6. It was shown that forces greater than 18400g(av.) for 2h have to be used before chick liver mitochondria reach isopycnic equilibrium. 7. As for rat liver mitochondria, the constant protein/phospholipid ratio of the B2 and B3 fractions and their apparent morphological intactness leads one to conclude that the matrix space of B2 mitochondria is inaccessible to sucrose, whereas B3 mitochondria possess an inner membrane that is permeable to sucrose.

Defective production of mitochondrial ribosomes in the poky mutant of Neurospora crassa

A strain of Neurospora crassa containing a cytoplasmic mutation (poky) affecting mitochondrial function is shown to be deficient in small ribosomal subunits in the mitochondrion during the exponential growth phase. In the stationary growth phase, small subunits are more abundant and are present in mitochondrial ribosomal monomers. This change can be correlated with the return of mitochondrial cytochrome content to amounts approaching those of wild type mitochondria. The ribosomal defect shows an extrachromosomal pattern of inheritance in crosses of poky with wild type.

Control of mitochondrial turnover under the influence of thyroid hormone

The effect of thyroid hormone on the turnover of mitochondrial DNA and protein was studied in rat heart and liver. Changes in turnover were observed in both thyroidectomized and normal rats following administration of thyroid hormone. In heart and liver the turnover of mitochondrial DNA and protein was slower in thyroidectomized rats than in normal rats. The turnover of mitochondrial DNA and protein was affected similarly following the administration of thyroid hormone, suggesting that mechanisms which control turnover of mitochondrial constituents may be predicated upon a major part of the mitochondrion. In heart a decreased rate of degradation contributes to the increase in total mitochondrial protein. Mitochondrial DNA, labeled before administration of thyroid hormone, turns over, after the start of thyroid hormone administration, at a different rate from that in newly synthesized DNA. The different turnover rates suggest that in liver the pre-existing population of mitochondria is being replaced by another population synthesized under new physiological conditions.

A multiple origin for plastids and mitochondria

The impressive homologies between mitochondria and plastids, on the one hand, and procaryotic organisms, on the other, make it almost certain that these important cellular organelles had their origin as independent organisms. The vast number of symbiotic relationships of all degrees of evolutionary antiquity which have been found in contemporary organisms point to the ease with which such relationships can be established.

Riboflavin and mouse hepatic cell structure and function. II. Division of mitochondria during recovery from simple deficiency

Mice which had been on a riboflavin-free diet for 6-8 wk were given daily intraperitoneal injections of riboflavin. The hepatic mitochondria, which in the deficient animals were greatly enlarged, were restored to normal dimensions within 3 days. Normalization of the mitochondrial population was brought about by division of the giant organelles. Dividing mitochondria were characterized by a membranous partition separating the inner compartment into two distinct chambers. Such organelles showed varying degrees of pinching at the level of the partition. The most common site of partition formation was at the base of a small mitochondrial bud. During the 1st day of recovery, dividing mitochondria were so common that they could be easily found in mitochondrial pellets. Injection of riboflavin into normally nourished mice also produced an apparent increase in the frequency of dividing mitochondria in the liver cells.

Ribosome particles in corn mitochondria

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Adaptation of Rhodopseudomonas spheroides

The composition of Rhodopseudomonas spheroides grown under oxygen or under air in the dark, or semi-anaerobically in the light was studied. The amounts of various constituents were expressed per cell. Anaerobically grown cells were 20 % lighter than cells grown under oxygen but contained approximately 50 % more protein and 85 % more phospholipid. The differences in weight were largely due to greater amounts of reserve material (poly-B-hydroxybutyrate and carbohydrate) in oxygen-grown cells. The major increase in the protein was due to a doubling of the 4particulate5 protein, the ‘soluble’ protein increasing by only 20% . The values of certain constituents in cells grown in air were intermediate between those of oxygen-grown cells and semi-anaerobically grown cells. The changes in composition were followed during adaptation from growth under oxygen to semi-anaerobic conditions in the light. Particulate protein, phospholipid, and enzymes concerned in bacteriochlorophyll synthesis increased markedly before photopigments or chromatophores were formed. These results indicate the sequence of some of the steps concerned in the differentiation of the cytoplasmic membrane of pigment-free microorganisms into the fully formed photosynthetic apparatus.

Structural modulations of plasmalemmal vesicles

Structural modulations affecting a small fraction of the population of plasmalemmal vesicles of vascular endothelia are described. They include forms which are apparently produced by the fusion of the vesicular membrane with the plasmalemma and by the successive elimination of the layers of the two fused membranes. Such modulations are assumed to represent stages in the discharge process of vesicular contents. Other forms, characterized by their flask shape and elongated neck, are assumed to represent stages in the formation and loading of membrane invaginations, followed by their being pinched off to form isolated vesicles. Stages in a membrane-fusion process leading to the formation of apertured fenestrae and channels are also described in fenestrated endothelia. The visualization of these structural details is greatly facilitated by staining tissue specimens with uranyl acetate before dehydration.

Riboflavin and mouse hepatic cell structure and function. I. Ultrastructural alterations in simple deficiency

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