An improved procedure for preparation of inner membrane vesicles from rat liver mitochondria by treatment with digitonin

Blocked O-GlcNAc cycling alters mitochondrial morphology, function, and mass

O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia.

Relationships between expression of BCS1L, mitochondrial bioenergetics, and fatigue among patients with prostate cancer

Introduction: Cancer-related fatigue (CRF) is the most debilitating symptom with the greatest adverse side effect on quality of life. The etiology of this symptom is still not understood. The purpose of this study was to examine the relationship between mitochondrial gene expression, mitochondrial oxidative phosphorylation, electron transport chain complex activity, and fatigue in prostate cancer patients undergoing radiotherapy (XRT), compared to patients on active surveillance (AS).

Methods: The study used a matched case–control and repeated-measures research design. Fatigue was measured using the revised Piper Fatigue Scale from 52 patients with prostate cancer. Mitochondrial oxidative phosphorylation, electron-transport chain enzymatic activity, and BCS1L gene expression were determined using patients’ peripheral mononuclear cells. Data were collected at three time points and analyzed using repeated measures ANOVA.

Results: The fatigue score was significantly different over time between patients undergoing XRT and AS (P<0.05). Patients undergoing XRT experienced significantly increased fatigue at day 21 and day 42 of XRT (P<0.01). Downregulated mitochondrial gene (BC1, ubiquinol-cytochrome c reductase, synthesis-like, BCS1L, P<0.05) expression, decreased OXPHOS-complex III oxidation (P<0.05), and reduced activity of complex III were observed over time in patients with XRT. Moreover, increased fatigue was significantly associated with downregulated BCS1L and decreased complex III oxidation in patients undergoing XRT.

Conclusion: Our results suggest that BCS1L and complex III in mitochondrial mononuclear cells are potential biomarkers and feasible therapeutic targets for acute XRT-induced fatigue in this clinical population.

Kummitha C, Rosca MG, Fujioka H, Tandler B, Hoppel CL. Isolation of mitochondrial subpopulations from skeletal muscle: Optimizing recovery and preserving integrity

AIM

The subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria in skeletal muscle appear to have distinct biochemical properties affecting metabolism in health and disease. The isolation of mitochondrial subpopulations has been a long-time challenge while the presence of a continuous mitochondrial reticulum challenges the view of distinctive SSM and IFM bioenergetics. Here, a comprehensive approach is developed to identify the best conditions to separate mitochondrial fractions.

METHODS

The main modifications to the protocol to isolate SSM and IFM from rat skeletal muscle were: (a) decreased dispase content and homogenization speed; (b) trypsin treatment of SSM fractions; (c) recentrifugation of mitochondrial fractions at low speed to remove subcellular components. To identify the conditions preserving mitochondrial function, integrity, and maximizing their recovery, microscopy (light and electron) were used to monitor effectiveness and efficiency in separating mitochondrial subpopulations while respiratory and enzyme activities were employed to evaluate function, recovery, and integrity.

RESULTS

With the modifications described, the total mitochondrial yield increased with a recovery of 80% of mitochondria contained in the original skeletal muscle sample. The difference between SSM and IFM oxidative capacity (10%) with complex-I substrate was significant only with a saturated ADP concentration. The inner and outer membrane damage for both subpopulations was <1% and 8%, respectively, while the respiratory control ratio was 16.

CONCLUSION

Using a multidisciplinary approach, conditions were identified to maximize SSM and IFM recovery while preserving mitochondrial integrity, biochemistry, and morphology. High quality and recovery of mitochondrial subpopulations allow to study the relationship between these organelles and disease.

Analyzing mitochondrial function in human peripheral blood mononuclear cells

Mitochondrial oxidative phosphorylation (OXPHOS) is responsible for producing most of the adenosine triphosphate required by eukaryotic cells. Lymphocytes make up the majority of the peripheral blood mononuclear cells. Peripheral blood mononuclear cells are readily obtainable, providing an ideal sample to monitor systemic changes and understand molecular signaling mechanisms in disease processes. Mitochondrial energy metabolism of lymphocyte has been used to screen for OXPHOS disorders. While there are increasing studies of lymphocyte OXPHOS, few studies examined activity of electron transport chain of lymphocyte mitochondria. We present an optimal protocol to harvest fresh peripheral blood mononuclear cells from human whole blood, determine integrated mitochondrial function, and analyze electron transport chain complex activity. Analyzing integrated mitochondrial function using OXPHOS provides data to uncover defects in the transport of substrates into the mitochondria, generation of reducing equivalents, the electron transport chain, and coupling to the production of adenosine triphosphate. The optimal conditions to harvest peripheral blood mononuclear cells were using blood anticoagulated with ethylenediaminetetraacetic acid, processed utilizing Lymphoprep™, and washed in phosphate buffered saline, all at room temperature. Using isolated peripheral blood mononuclear cells, integrated mitochondrial function and the activities of electron transport chain were determined.

Defects in skeletal muscle subsarcolemmal mitochondria in a non-obese model of type 2 diabetes mellitus

Skeletal muscle resistance to insulin is related to accumulation of lipid-derived products, but it is not clear whether this accumulation is caused by skeletal muscle mitochondrial dysfunction. Diabetes and obesity are reported to have a selective effect on the function of subsarcolemmal and interfibrillar mitochondria in insulin-resistant skeletal muscle. The current study investigated the role of the subpopulations of mitochondria in the pathogenesis of insulin resistance in the absence of obesity. A non-obese spontaneous rat model of type 2 diabetes mellitus, (Goto-Kakizaki), was used to evaluate function and biochemical properties in both populations of skeletal muscle mitochondria. In subsarcolemmal mitochondria, minor defects are observed whereas in interfibrillar mitochondria function is preserved. Subsarcolemmal mitochondria defects characterized by a mild decline of oxidative phosphorylation efficiency are related to ATP synthase and structural alterations of inner mitochondria membrane but are considered unimportant because of the absence of defects upstream as shown with polarographic and spectrophometric assays. Fatty acid transport and oxidation is preserved in both population of mitochondria, whereas palmitoyl-CoA increased 25% in interfibrillar mitochondria of diabetic rats. Contrary to popular belief, these data provide compelling evidence that mitochondrial function is unaffected in insulin-resistant skeletal muscle from T2DM non-obese rats.

Anesthetic considerations in patients with mitochondrial defects

Mitochondrial disease, once thought to be a rare clinical entity, is now recognized as an important cause of a wide range of neurologic, cardiac, muscle, and endocrine disorders . The incidence of disorders of the respiratory chain alone is estimated to be about 1 per 4-5000 live births, similar to that of more well-known neurologic diseases . High-energy requiring tissues are uniquely dependent on the energy delivered by mitochondria and therefore have the lowest threshold for displaying symptoms of mitochondrial disease. Thus, mitochondrial dysfunction most commonly affects function of the central nervous system, the heart and the muscular system . Mutations in mitochondrial proteins cause striking clinical features in those tissues types, including encephalopathies, seizures, cerebellar ataxias, cardiomyopathies, myopathies, as well as gastrointestinal and hepatic disease. Our knowledge of the contribution of mitochondria in causing disease or influencing aging is expanding rapidly . As diagnosis and treatment improve for children with mitochondrial diseases, it has become increasingly common for them to undergo surgeries for their long-term care. In addition, often a muscle biopsy or other tests needing anesthesia are required for diagnosis. Mitochondrial disease represents probably hundreds of different defects, both genetic and environmental in origin, and is thus difficult to characterize. The specter of possible delayed complications in patients caused by inhibition of metabolism by anesthetics, by remaining in a biochemically stressed state such as fasting/catabolism, or by prolonged exposure to pain is a constant worry to physicians caring for these patients. Here, we review the considerations when caring for a patient with mitochondrial disease.

Complex I function is defective in complex IV-deficient Caenorhabditis elegans

Cytochrome c oxidase (COX) is hypothesized to be an important regulator of oxidative phosphorylation. However, no animal phenotypes have been described due to genetic defects in nuclear-encoded subunits of COX. We knocked down predicted homologues of COX IV and COX Va in the nematode Caenorhabditis elegans. Animals treated with W09C5.8 (COX IV) or Y37D8A.14 (COX Va) RNA interference had shortened lifespans and severe defects in mitochondrial respiratory chain function. Amount and activity of complex IV, as well as supercomplexes that included complex IV, were decreased in COX-deficient worms. The formation of supercomplex I:III was not dependent on COX. We found that COX deficiencies decreased intrinsic complex I enzymatic activity, as well as complex I-III enzymatic activity. However, overall amounts of complex I were not decreased in these animals. Surprisingly, intrinsic complex I enzymatic activity is dependent on the presence of complex IV, despite no overall decrease in the amount of complex I. Presumably the association of complex I with complex IV within the supercomplex I:III:IV enhances electron flow through complex I. Our results indicate that reduction of a single subunit within the electron transport chain can affect multiple enzymatic steps of electron transfer, including movement within a different protein complex. Patients presenting with multiple defects of electron transport may, in fact, harbor a single genetic defect.

Effect of intermittent normobaric hypoxia on kinetic properties of mitochondrial enzymes

We studied the effect of intermittent normobaric hypoxia on the formation of adaptive signs and state of mitochondrial enzymes in the cerebral cortex of rats with different resistance to hypoxia. Kinetic parameters for mitochondrial enzymes in the substrate region of the respiratory chain of the cerebral cortex underwent various changes in low resistant and highly resistant rats over the first 2 h after 1-h intermittent normobaric hypoxia. Low resistant animals were characterized by more effective functioning of rotenone-sensitive NADH-cytochrome C reductase and succinate-cytochrome C reductase under conditions of increased reduction status of the cell. These features correlated with the increase in the general resistance of animals. Significant changes in kinetic properties of mitochondrial enzymes and signs of the development of resistance were not found in highly resistant rats. Reciprocal relations between mitochondrial enzyme complexes in the substrate region of the respiratory chain probably play a role of the signal regulatory mechanism, which mediates tissue-specific and general resistance of rats under conditions of intermittent normobaric hypoxia. These effects did not depend on oxygenation of the inhaled gas mixture during the inter-hypoxic period.

Deficiency of the ADP-forming succinyl-CoA synthase activity is associated with encephalomyopathy and mitochondrial DNA depletion

The mitochondrial DNA (mtDNA) depletion syndrome is a quantitative defect of mtDNA resulting from dysfunction of one of several nuclear-encoded factors responsible for maintenance of mitochondrial deoxyribonucleoside triphosphate (dNTP) pools or replication of mtDNA. Markedly decreased succinyl-CoA synthetase activity due to a deleterious mutation in SUCLA2, the gene encoding the beta subunit of the ADP-forming succinyl-CoA synthetase ligase, was found in muscle mitochondria of patients with encephalomyopathy and mtDNA depletion. Succinyl-CoA synthetase is invariably in a complex with mitochondrial nucleotide diphosphate kinase; hence, we propose that a defect in the last step of mitochondrial dNTP salvage is a novel cause of the mtDNA depletion syndrome.

Defective mitochondrial translation caused by a ribosomal protein (MRPS16) mutation

The mitochondrial respiratory chain comprises 85 subunits, 13 of which are mitochondrial encoded. The synthesis of these 13 proteins requires many nuclear-encoded proteins that participate in mitochondrial DNA replication, transcript production, and a distinctive mitochondrial translation apparatus. We report a patient with agenesis of corpus callosum, dysmorphism, and fatal neonatal lactic acidosis with markedly decreased complex I and IV activity in muscle and liver and a generalized mitochondrial translation defect identified in pulse-label experiments. The defect was associated with marked reduction of the 12S rRNA transcript level likely attributed to a nonsense mutation in the MRPS16 gene. A new group of mitochondrial respiratory chain disorders is proposed, resulting from mutations in nuclear encoded components of the mitochondrial translation apparatus.

Mutant mitochondrial thymidine kinase in mitochondrial DNA depletion myopathy

The mitochondrial deoxyribonucleotide (dNTP) pool is separated from the cytosolic pool because the mitochondria inner membrane is impermeable to charged molecules. The mitochondrial pool is maintained by either import of cytosolic dNTPs through dedicated transporters or by salvaging deoxynucleosides within the mitochondria; apparently, enzymes of the de novo dNTP synthesis pathway are not present in the mitochondria. In non-replicating cells, where cytosolic dNTP synthesis is down-regulated, mtDNA synthesis depends solely on the mitochondrial salvage pathway enzymes, the deoxyribonucleosides kinases. Two of the four human deoxyribonucleoside kinases, deoxyguanosine kinase (dGK) and thymidine kinase-2 (TK2), are expressed in mitochondria. Human dGK efficiently phosphorylates deoxyguanosine and deoxyadenosine, whereas TK2 phosphorylates deoxythymidine, deoxycytidine and deoxyuridine. Here we identify two mutations in TK2, histidine 90 to asparagine and isoleucine 181 to asparagine, in four individuals who developed devastating myopathy and depletion of muscular mitochondrial DNA in infancy. In these individuals, the activity of TK2 in muscle mitochondria is reduced to 14-45% of the mean value in healthy control individuals. Mutations in TK2 represent a new etiology for mitochondrial DNA depletion, underscoring the importance of the mitochondrial dNTP pool in the pathogenesis of mitochondrial depletion.

Aging selectively decreases oxidative capacity in rat heart interfibrillar mitochondria

Mitochondrial-derived oxidative injury contributes to cellular aging as well as to reperfusion-induced tissue damage. While the aging-heart suffers greater tissue damage following ischemia and reperfusion than the adult heart, the occurrence of aging-related alterations in mitochondrial oxidative metabolism in the elderly heart has remained uncertain. We determined if aging altered oxidative metabolism in either of the two populations of cardiac mitochondria, subsarcolemmal mitochondria (SSM) that reside beneath the plasma membrane or interfibrillar mitochondria (IFM) located between the myofibrils. SSM and IFM were isolated from 6-month adult and 24- and 28-month elderly Fischer 344 rat hearts. Aging-related alterations were limited to IFM, while SSM remained unaffected. Aging decreased the rate of oxidative phosphorylation in IFM, including when stimulated by electron donors specific for cytochrome oxidase. Cytochrome oxidase enzyme activity was decreased in IFM from aging hearts, while activity in SSM remained similar to adult controls. These findings allow future studies of aging-related decrements in oxidative function to focus upon IFM, while SSM provide an inherent control group of mitochondria that are free of aging-related alterations in oxidative function. The selective alteration of IFM during aging raises the possibility that the consequences of aging-induced mitochondrial dysfunction will be enhanced in specific subcellular regions of the senescent myocyte.

Lipoamide dehydrogenase deficiency due to a novel mutation in the interface domain

An infant with a neurodegenerative disorder accompanied by lactic acidemia is described. In muscle homogenate, the activity of lipoamide dehydrogenase (LAD), the third catalytic subunit of pyruvate dehydrogenase complex (PDHc), alpha-ketoglutarate dehydrogenase complex (KGDHc), and branched-chain keto acid dehydrogenase complex was reduced to 15% of the control. The activity of PDHc was undetectable and the activity of KGDHc was 2% of the control mean. The immunoreactive LAD protein was reduced to about 10% of the control. Direct sequencing of LAD cDNA revealed only one mutation, substituting Asp for Val at position 479 of the precursor form. The mutation resides within the interface domain and likely perturbs stable dimerization. The phenotypic heterogeneity in LAD deficiency is not directly correlated with the residual LAD activity but rather with its impact on the multienzymatic complex activity.

Mitochondrial encephalomyopathy associated with a novel mutation in the mitochondrial tRNA(leu)(UUR) gene (A3243T)

We report a new mutation, an A-->T transition at nt 3243 in the mitochondrial tRNA(leu)(UUR) gene, in a 9-year-old girl who presented with muscle weakness of 3 years duration complicated by rapidly progressive encephalopathy. In muscle, the activity of the mitochondrial respiratory chain complexes I, III, and IV was markedly reduced. The mutation, involving a highly conserved base pair in the dihydrouridine loop, was heteroplasmic in muscle (81.4%), skin (69.3%), and blood (13.8%) and was not present in blood of 50 healthy individuals. The mitochondrial 3243 base is a "hot spot" for mutations; an A-->G transition at this position is found in a high proportion in most MELAS patients. Since the A-->T transition creates a new recognition site for the restriction enzyme TspRI, both ApaI and TspRI should be used to exclude a mutation at nt 3243.

Mechanisms of impaired hepatic fatty acid metabolism in rats with long-term bile duct ligation

Hepatic metabolism of fatty acids is impaired in experimental animals with long-term bile duct ligation. To characterize the underlying defects, fatty acid metabolism was investigated in isolated hepatocytes and isolated liver mitochondria from rats subjected to long-term bile duct ligation or sham surgery. After starvation for 24 hr, the plasma beta-hydroxybutyrate concentration was decreased in rats with bile duct ligation as compared with control rats. Production of beta-hydroxybutyrate from butyrate, octanoate and palmitate by hepatocytes isolated from rats subjected to bile duct ligation was also decreased. Liver mitochondria from rats subjected to bile duct ligation showed decreased state 3 oxidation rates for L-glutamate, succinate, duroquinone, and fatty acids but not for ascorbate as substrate. State 3u oxidation rates (uncoupling with dinitrophenol) and activities of mitochondrial oxidases were also decreased in mitochondria from rats subjected to bile duct ligation. Direct assessment of the activities of the subunits of the electron transport chain revealed reduced activities of complex I, complex II and complex III in mitochondria from rats subjected to bile duct ligation. Activities of the beta-oxidation enzymes specific for short-chain fatty acids were all reduced in rats subjected to bile duct ligation. Mitochondrial protein content per hepatocyte was increased by 32% in rats subjected to bile duct ligation compared with control rats. Thus the studies directly demonstrate mitochondrial defects in fatty acid oxidation in rats subjected to bile duct ligation, which explain decreased ketosis during starvation.

Mitochondrial encephalomyopathies in childhood. I. Biochemical and morphologic investigations

During a 4-year period (1984 to 1988), 50 children referred with manifestations of central nervous system or neuromuscular disease combined with hyperlactatemia were subjected to investigations that aimed to identify and characterize children with mitochondrial disorders. Biochemical and morphologic investigations of quadriceps muscle biopsy tissue were done, including oximetric and spectrophotometric analysis of the respiratory chain function, enzyme histochemistry, electron microscopy, and analysis of mitochondrial DNA. A diagnosis of mitochondrial disease was based on the presence of at least two of five criteria: (1) abnormal results of oximetry, (2) abnormal results of spectrophotometry, (3) enzyme histochemical evidence of cytochrome x oxidase deficiency, (4) deletions or point mutations of mitochondrial DNA, and (5) abundant ultrastructurally abnormal mitochondria. With the combined biochemical and morphologic investigation, 20 of the children were found to have mitochondrial disorders. In an additional 10 children a mitochondrial disorder was neither excluded nor verified. Mitochondrial disorders are thus an important cause of central nervous system and neuromuscular disease in children with hyperlactatemia.

Cytochrome c oxidase deficiency in infancy

Five children with early onset of muscle weakness, lactic acidosis and deficient cytochrome c oxidase staining in the muscle biopsy were studied. By oximetric assay of the respiratory chain of isolated mitochondria, cytochrome c oxidase deficiency was confirmed in four of the cases, while one case showed only a slight decrease of cytochrome c oxidase activity but considerably reduced activity when assayed spectrophotometrically. The muscle biopsies exhibited mitochondrial structural abnormalities and lipid storage in the four cases with oximetrically confirmed cytochrome c oxidase deficiency, while the biopsy of the case with markedly reduced activity of cytochrome c oxidase only in the enzyme-histochemical and spectrophotometrical assays had normal morphology. The light microscopical staining of cytochrome c oxidase in the four cases with oximetrically confirmed deficiency showed deficient staining of the enzyme in all extrafusal fibres in three cases but one of the cases had normal enzyme-histochemical activity of cytochrome c oxidase in about 25% of the fibres. In two cases muscle spindles were included in the biopsy. The intrafusal fibres showed normal enzyme-histochemical activity of cytochrome c oxidase. Ultrastructural examination of the enzyme distribution in two of the cases revealed great heterogeneity of the mitochondria. The structurally abnormal mitochondria were usually deficient of enzyme activity. The mitochondria of endothelial cells appeared to have normal activity. Immunohistochemical staining with polyclonal antibodies to cytochrome c oxidase revealed presence of immunoreactive material corresponding to the localisation of mitochondria in all cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Deficiency of the reduced nicotinamide adenine dinucleotide dehydrogenase component of complex I of mitochondrial electron transport. Fatal infantile lactic acidosis and hypermetabolism with skeletal-cardiac myopathy and encephalopathy

A mitochondrial defect was investigated in an infant with fatal congenital lactic acidosis (3-14 mM), high lactate-to-pyruvate ratio, hypotonia, and cardiomyopathy. His sister had died with a similar disorder. Resting oxygen consumption was 150% of controls. Pathological findings included increased numbers of skeletal muscle mitochondria (many with proliferated, concentric cristae), cardiomegaly, fatty infiltration of the viscera, and spongy encephalopathy. Mitochondria from liver and muscle biopsies oxidized NADH-linked substrates at rates 20-50% of controls, whereas succinate oxidation by muscle mitochondria was increased. Mitochondrial NADH dehydrogenase activity (complex I, assayed as rotenone-sensitive NADH oxidase, NADH-duroquinone reductase, and NADH-cytochrome c reductase) was 0-10% of controls, and NADH-ferricyanide reductase activity was 25-50% of controls in the mitochondria and in skin fibroblasts. Activities of other electron transport complexes and related enzymes were normal. Familial deficiency of a component of mitochondrial NADH dehydrogenase (complex I) proximal to the rotenone-sensitive site thus accounts for this disorder.

Fumarase deficiency: a new cause of mitochondrial encephalomyopathy

We observed a deficiency of both the mitochondrial and cytosolic forms of fumarase in a male infant with mitochondrial encephalomyopathy who presented at one month of age with failure to thrive, developmental delay, hypotonia, cerebral atrophy, lactic and pyruvic acidemia, and fumaric aciduria. The patient died at eight months of age. Isolated skeletal-muscle mitochondria showed selective defects in the oxidation of glutamate (31 ng atoms of oxygen consumed per minute per milligram of mitochondrial protein, as compared with 94 +/- 19 [mean +/- SD] in five controls) and of succinate (18 vs. 145 +/- 18 ng atoms of oxygen per minute per milligram of protein), whereas isolated liver mitochondria oxidized these and other substrates normally. Fumarase activity was virtually absent in both liver mitochondria (53 vs. 2878 +/- 248 nmol per minute per milligram of protein [5 controls]) and skeletal-muscle mitochondria (23 vs. 1997 +/- 717 nmol per minute per milligram [12 controls]). Seventeen other mitochondrial enzymes had normal activity in both liver and muscle mitochondrial extracts. Fumarase activity was also significantly reduced in homogenates of liver tissue (less than 1 vs. 90 +/- 25 mumol per minute per gram of wet weight [five controls]) and skeletal muscle (less than 1 vs. 21 +/- 4 mumol per minute per gram [five controls]), indicating a deficiency of both mitochondrial and cytosolic fumarases. Organ differences in intramitochondrial accumulation of fumarate may have accounted for the selective oxidative defects observed in the skeletal-muscle mitochondria but not liver mitochondria. All these findings are consistent with a profound combined fumarase deficiency.

Digitonin induced alterations of the erythrocyte membrane as visible by freeze-fracturing

Treatment of erythrocytes by low concentrations of digitonin results in the formation of elongated, bulged membrane areas free from particles and intramembraneous tubular structures emerged from these domains. At higher concentrations the tubular structures are present also outside of the membrane. A second, not bulged type of particle-free areas is more or less rounded, but mostly of rectangular shape. The rate of this type of domains increases with the concentration of digitonin. Breaks in these areas lead to a formation of sheets which results in a breakdown of the membrane structure finally into a brittle mass of many small sheets lying irregularly one upon the other. Already during the first steps of this membrane breakdown hemolysis takes place. Cross-linking of the proteins with glutaraldehyde does not entirely block up the membrane alterations. In fixed erythrocytes the formation fo elongated domains is restricted, no tubular structures are present and no dislocations of particles can be observed. Nevertheless smooth sheets localized also outside of the membrane are formed. However the investigated ghosts are not stabilized by glutaraldehyde against the effects of digitonin. Particle dislocations as well as all the other membrane alterations are present. The implications of the obtained results are: 1. The elongated domains and the tubular structures are probably not digitonin-cholesterol-complexes. 2. The formation of crystalline regions by digitonin-cholesterol-complexes destroys the membrane structure.