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PubMed2000

Mitochondrial function in flying honeybees (Apis mellifera): respiratory chain enzymes and electron flow from complex III to oxygen.

The biochemical bases for the high mass-specific metabolic rates of flying insects remain poorly understood. To gain insights into mitochondrial function during flight, metabolic rates of individual flying honeybees were measured using respirometry, and their thoracic muscles were fixed for electron microscopy. Mitochondrial volume densities and cristae surface densities, combined with biochemical data concerning cytochrome content per unit mass, were used to estimate respiratory chain enzyme densities per unit cristae surface area. Despite the high content of respiratory enzymes per unit muscle mass, these are accommodated by abundant mitochondria and high cristae surface densities such that enzyme densities per unit cristae surface area are similar to those found in mammalian muscle and liver. These results support the idea that a unit area of mitochondrial inner membrane constitutes an invariant structural unit. Rates of O(2) consumption per unit cristae surface area are much higher than those estimated in mammals as a consequence of higher enzyme turnover rates (electron transfer rates per enzyme molecule) during flight. Cytochrome c oxidase, in particular, operates close to its maximum catalytic capacity (k(cat)). Thus, high flux rates are achieved via (i) high respiratory enzyme content per unit muscle mass and (ii) the operation of these enzymes at high fractional velocities.

Animals↗
PubMedDate not supplied

[Ultrastructural localization of the oxydasic activity in Toxoplasma gondii (author's transl)].

Toxoplasma belonging on the RH strain were studied under a transmission electron microscope. The activities looked for were: peroxidase, cytochrome oxydase and acid phosphatase. An oxydasic cytochrome respiratory activity was seen. It is localised on the crests and on the peripheral membrane of the mitochondria of Toxoplasma gondii. In the given experimental conditions, no such activity appeared in the other intracytoplasmic organels of the parasite, nor in the vacuoles of the host-cells containing living toxoplasma but the organels of those host-cells presented an oxydasic activity.

Acid Phosphatase↗
PubMed1990

Cytochrome c oxidase activity in preosteoclasts induced by experimental tooth movement.

Cytochrome c oxidase activity was detected in preosteoclasts induced by experimental tooth movement. Mitochondria with reaction products of the enzyme in the inner membrane and outer compartment, which we classified as type 1 mitochondria, were observed in preosteoclasts. The number of type 1 mitochondria in the preosteoclasts, however, was distinctly fewer as compared with those in active osteoclasts described in our previous studies. Also, some of preosteoclasts adjacent to the bone surface contained more type 1 mitochondria than preosteoclasts separated from the bone surface. These results suggest that cytochrome c oxidase activity is closely related to functional differentiation of preosteoclasts, and additionally can be used as an indicator of functional differentiation from preosteoclast to osteoclast.

Animals↗
PubMed1981

Mitochondrial number, cytochrome oxidase and succinic dehydrogenase activity in Xenopus laevis oocytes.

An estimate has been made of the numbers of mitochondria in the mitochondrial cloud (Balbiani body) of Xenopus laevis oocytes ranging in size from 50 to 250 micrometers. The mitochondrial number is expressed in terms of a 'standard' organelle measuring 2 micrometers in length and 0.2 micrometer in diameter and is derived by measurements on electron micrographs of sections through the cloud. It is found that the amount of mitochondrial material rises very rapidly as the oocyte grows in size. At the time the cloud disperses, in oocytes of about 300 micrometers in diameter, it is estimated that there are the equivalent of over 500 000 mitochondria in each cell. The rate of increase is very similar to the rate of accumulation of mitochondrial DNA during the same period of growth. Using a polarographic technique the specific activity of cytochrome oxidase and succinic dehydrogenase was determined in mitochondrial fractions isolated from oocytes over a size range of 80-1200 micrometers in diameter. Although the specific activity of succinic dehydrogenase remains constant that of cytochrome oxidase falls sharply during the period when the mitochondria are replicating rapidly, i.e. up to about 300 micrometer diameter. In larger oocytes the specific activity of enzymes appears to remain constant but increasing contamination of the isolated mitochondrial fraction does not allow conclusions to be drawn from the enzyme loading of the mitochondria once they have dispersed from the cloud. The results are discussed in relation to the possibility that mitochondrial replication preceeds, or at least outpaces, mitochondrial differentiation during the course of oogenesis.

Animals↗
PubMedDate not supplied

Familial spastic paraparesis: a case of a mitochondrial disorder.

Familial spastic paraparesis is characterized by progressive gait disturbance without associated sensory, cerebellar, or cranial nerve deficits. Mitochondrial disorders are associated with heterogenic clinical presentations, though not with spastic paraparesis. A patient with familial spastic paraparesis had deficiencies of respiratory chain enzyme complex I, III, and IV. Progressive spasticity was arrested after treatment with coenzyme Q, carnitine, vitamin C and K. Familial spastic paraparesis may represent a mitochondrial disorder.

Biopsy↗
PubMed2001

Traumatic brain injury-induced changes in gene expression and functional activity of mitochondrial cytochrome C oxidase.

Traumatic brain injury (TBI) is documented to have detrimental effects on CNS metabolism, including alterations in glucose utilization and the depression of mitochondrial oxidative phosphorylation. Studies on mitochondrial metabolism have also provided evidence for reduced activity of the cytochrome oxidase complex of the electron transport chain (complex IV) after TBI and an immediate (lhr) reduction in mitochondrial state 3 respiratory rate, which can persist for up to 14 days postinjury. Using differential display methods to screen for differences in gene expression, we have found that cytochrome c oxidase II (COII), a mitochondrial encoded subunit of complex IV, is upregulated following TBI. Since COII carries a binding site for cytochrome c in the respiratory chain, and since it is required for the passage of chain electrons to molecular oxygen, driving the production of ATP, we hypothesized that metabolic dysfunction resulting from TBI alters COII gene expression directly, perhaps influencing the synaptic plasticity that occurs during postinjury recovery processes. To test this hypothesis, we documented COII mRNA expression and complex IV (cytochrome c oxidase) functional activity at 7 days postinjury, focusing on the long-term postinjury period most closely associated with synaptic reorganization. Both central fluid percussion TBI and combined TBI and bilateral entorhinal cortical lesion were examined. At 7 days survival, differential display, RT-PCR, and Northern blot analysis of hippocampal RNA from both TBI and combined insult models showed a significant induction of COII mRNA. This long-term elevation in COII gene expression was supported by increases in COII immunobinding. By contrast, cytochrome oxidase histochemical activity within tissue sections from injured brains suggested a reduction of complex IV activity within the TBI cases, but not within animals subjected to the combined insult. These differences in cytochrome c oxidase activity were supported by in vitro assay of complex IV using cerebral cortical and hippocampal tissues. Our present results support the hypothesis that COII is selectively vulnerable to TBI and that COII differences may indicate the degree of metabolic dysfunction induced by different pathologies. Taken together, such data will better define the role of metabolic function in long-term recovery after TBI.

Animals↗
PubMed1978

Structure and orientation of cytochrome c oxidase in crystalline membranes. Studies by electron microscopy and by labeling with subunit-specific antibodies.

The structure and the orientation of cytochrome c oxidase molecules in crystalline cytochrome c oxidase membranes (Vanderkooi, G., Senior, A.E., Capaldi, R.A., and Hayashi, H. (1972) Biochim. Biophys. Acta 274, 38-48) were studied by image analysis of electron micrographs and by reacting the crystalline preparations with immune gamma-globulins against individual cytochrome c oxidase subunits. Binding of gamma-globulins to the membranes was detected by the following two methods: (a) electrophoretic identification of gamma-globulin polypeptides in the washed membranes; (b) electron microscopic examination of the negatively stained membranes. The membranes bound immune gamma-globulins against subunit IV (which faces the matrix side in intact mitochondria) but failed to bind immune gamma-globulins against subunits II + III (which face the outer side of the inner membrane in intact mitochondria). In contrast, solubilized cytochrome c oxidase bound either of the two immune gamma-globulins. All cytochrome c oxidase molecules in the crystalline membranes are thus asymmetrically arranged so that subunit IV faces outward and subunits II + III face toward the interior. This orientation is opposite to that found with intact mitochondria. The data also suggest that the crystalline membranes form closed vesicles which are impermeable to externally added gamma-globulins.

Animals↗