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PubMed2000

Thyroid hormone regulation of the NADH shuttles in liver and cardiac mitochondria.

Thyroid hormone can potentially regulate the malate/aspartate and alpha-glycerophosphate shuttle pathways in cardiac mitochondria either directly, by altering gene expression, or indirectly, by increasing myocardial workload. The goal of the current study was to determine the influence of thyroid hormone on the NADH shuttles in cardiac and liver mitochondria. Malate/aspartate and alpha-glycerophosphate shuttle capacities were significantly increased in cardiac mitochondria from adult rats treated for 9 days with T3 compared to saline-treated controls. Liver mitochondria demonstrated a significant increase in alpha-glycerophosphate and no change in malate/aspartate shuttle capacity. T3 increased steady-state mRNA levels and activity of mitochondrial alpha-glycerophosphate dehydrogenase in both myocardium and liver. Quantitative immunoblot studies demonstrated a significant increase in aspartate-glutamate carrier levels in T3-treated myocardium suggesting a regulatory role of the aspartate/glutamate carrier in T3-treated hearts. Thyroid hormone effects on the NADH shuttles are tissue-specific. Changes in the NADH shuttles in the presence of thyroid hormone excess occur both directly at the gene level and indirectly as an adaptive response.

Animals↗

PubMed1984

sn-Glycerol-3-phosphate acyltransferase in a particulate fraction from maturing safflower seeds.

The properties of the acyl-CoA:sn-glycerol-3-phosphate O-acyltransferase in a 20,000g particulate fraction from maturing safflower seeds were investigated. The optimum pH of the reaction was 7.2. The apparent Km for glycerophosphate was 0.54 mM. Only monoacylglycerophosphate was accumulated in the particulate fraction under normal conditions. Position 1 of glycerophosphate was exclusively esterified with either palmitoyl-CoA or linoleoyl-CoA as acyl donor, while 2-acylglycerophosphate was the minor product. The specificity and selectivity of the acyltransferase for acyl-CoA were broad and somewhat affected by temperature. The concentration of glycerophosphate did not affect the selectivity. These observations suggested that the fatty acid composition of position 1 of safflower triacylglycerol must primarily depend on the composition of the acyl-CoA pool in the site of synthesis, and that growth temperature and the acyl-CoA selectivity of the glycerophosphate acyltransferase may be rather minor factors regarding regulation of the fatty acid composition of position 1 in triacylglycerol.

Acyl Coenzyme A↗

PubMed2002

Phosphorus and uremic serum up-regulate osteopontin expression in vascular smooth muscle cells.

BACKGROUND: Dialysis patients have accelerated atherosclerosis, with extensive calcification of both the intima and media. Cross-sectional studies have implicated hyperphosphatemia in this process, but the mechanism is unclear. METHODS: To test the hypothesis that hyperphosphatemia and/or uremia induces vascular calcification, bovine vascular smooth muscle cells (BVSMC) were treated with increasing concentrations of beta-glycerophosphate, a phosphate donor, in the presence or absence of inhibitors for sodium/phosphate (Na/Pi) co-transport (foscarnet) or alkaline phosphatase (levamisole) for 48 hours. BVSMC also were incubated for various times with DMEM plus 15% pooled uremic sera from patients with low (LP) or high serum phosphorus (HP), or from pooled healthy control serum. Calcification in BVSMC was examined by quantitation of calcium deposition. Osteopontin expression and alkaline phosphatase activity were assessed by Western blotting and a colorimetric assay. RESULTS: beta-glycerophosphate increased osteopontin expression and alkaline phosphatase activity in BVSMC. Inhibition of either alkaline phosphatase activity or Na/Pi co-transport abolished this effect. Compared to incubation with control human serum, BVSMC cultured with uremic sera had increased mineral deposition. Uremic sera also increased alkaline phosphatase activity and osteopontin expression in BVSMC. The addition of beta-glycerophosphate to uremic HP or LP sera did not further augment osteopontin expression. Blocking Na/Pi co-transport or alkaline phosphatase activity only partially inhibited uremic sera-induced osteopontin expression, indicating that other non-Na/Pi co-transport dependent mechanisms also are involved. CONCLUSION: beta-glycerophosphate and uremic sera induce calcification and osteopontin expression in BVSMC. The uremic sera-induced osteopontin expression in BVSMC is partially mediated through alkaline phosphatase activity and a Na/Pi co-transporter dependent mechanism. However, other non-Na/Pi dependent mechanisms also contribute to accelerated vascular calcification in patients with ESRD.

Alkaline Phosphatase↗

PubMed1984

In vivo effects of microinjected alkaline phosphatase and its low molecular weight substrates on the first meiotic cell division in Xenopus laevis oocytes.

Xenopus laevis oocytes were microinjected with low molecular weight phosphoesters such as 2-glycerophosphate, phosphotyrosine, phosphoserine, phosphothreonine, 4-nitrophenyl phosphate, and orthophosphate. These compounds were able to induce a considerable reduction in the time course of progesterone-induced maturation, with 2-glycerophosphate being the most effective. The basal level of cAMP and its drop during maturation were not affected by the microinjection of 2-glycerophosphate. The injection of alkaline phosphatase (EC 3.1.3.1.) from calf intestine at a low concentration (10 ng per oocyte) was able to decrease or abolish the effect of 2-glycerophosphate. At higher concentration (25 ng per oocyte) this enzyme totally blocked progesterone- or maturation-promoting factor-induced maturation. Alkaline phosphatase might behave in vivo as a phosphoprotein phosphatase active towards phosphotyrosine-containing proteins. In addition, our results indicate that phosphate or phosphoester-containing buffers should be avoided in the course of maturation-promoting factor purification.

Alkaline Phosphatase↗

PubMed2004

Shift in the localization of sites of hydrogen peroxide production in brain mitochondria by mitochondrial stress.

We have determined the underlying sites of H(2)O(2) generation by isolated rat brain mitochondria and how these can shift depending on the presence of respiratory substrates, electron transport chain modulators and exposure to stressors. H(2)O(2) production was determined using the fluorogenic Amplex red and peroxidase system. H(2)O(2) production was higher when succinate was used as a respiratory substrate than with another FAD-dependent substrate, alpha-glycerophosphate, or with the NAD-dependent substrates, glutamate/malate. Depolarization by the uncoupler p-trifluoromethoxyphenylhydrazone decreased H(2)O(2) production stimulated by all respiratory substrates. H(2)O(2) production supported by succinate during reverse transfer of electrons was decreased by inhibitors of complex I (rotenone and diphenyleneiodonium) whereas in glutamate/malate-oxidizing mitochondria diphenyleneiodonium decreased while rotenone increased H(2)O(2) generation. The complex III inhibitors antimycin and myxothiazol decreased succinate-induced H(2)O(2) production but stimulated H(2)O(2) production in glutamate/malate-oxidizing mitochondria. Antimycin and myxothiazol also increased H(2)O(2) production in mitochondria using alpha-glycerophosphate as a respiratory substrate. In substrate/inhibitor experiments maximal stimulation of H(2)O(2) production by complex I was observed with the alpha-glycerophosphate/antimycin combination. In addition, three forms of in vitro mitochondrial stress were studied: Ca(2+) overload, cold storage for more than 24 h and cytochrome c depletion. In each case we observed (i) a decrease in succinate-supported H(2)O(2) production by complex I and an increase in succinate-supported H(2)O(2) production by complex III, (ii) increased glutamate/malate-induced H(2)O(2) generation by complex I and (iii) increased alpha-glycerophosphate-supported H(2)O(2) generation by complex III. Our results suggest that all three forms of mitochondrial stress resulted in similar shifts in the localization of sites of H(2)O(2) generation and that, in both normal and stressed states, the level and location of H(2)O(2) production depend on the predominant energetic substrate.

Animals↗

PubMed1976

Enzymes of carbohydrate metabolism in four human species of Leishmania: a comparative survey.

The occurrence and levels of activity of various enzymes of carbohydrate catabolism in culture forms (promastigotes) of 4 human species of Leishmania (L. brasiliensis, L. donovani, L. mexicana, and L. tropica) were compared. These organisms possess enzymes of the Embden-Meyerhof pathway but lack lactate dehydrogenase. No evidence could be found for the production of lactic acid by growing cultures and lactic acid could not be detected either in cell-free preparations or after incubation of cell-free extracts with pyruvate and NADH under appropriate conditions. All 4 species possess alpha-glycerophosphate dehydrogenase and alpha-glycerophosphate phosphatase which together could regenerate NAD, thus compensating for the absence of lactate dehydrogenase. The oxidative and nonoxidative reactions of the hexose monophosphate pathway are present in all 4 species. Cell-free extracts have pyruvate dehydrogenase activity which allows the entry of pyruvate into and its subsequent oxidation through the tricarboxylic acid cycle. All enzymes of this cycle, including a thiamine pyrophosphate dependent alpha-ketoglutarate dehydrogenase, are present. Both NAD and NADP-linked malate dehydrogenase activities are present. The isocitrate dehydrogenase is NADP specific. There is an active glutamate dehydrogenase which could compete with alpha-ketoglutarate dehydrogenase for the common substrate (alpha-ketoglutarate). Replenishment of C4 acids is accomplished by heterotrophic CO2 fixation catalyzed by pyruvate carboxylase. All 4 species have high levels of NADH oxidase activity. Several enzymes thus far not found in any species of Leishmania have been demonstrated. These are: phosphoglucose isomerase, triose phosphate isomerase, fructose-1, 6-diphosphatase, 3-phosphoglycerate kinase, enolase, alpha-glycerophosphate dehydrogenase, alpha-glycerophosphate phosphatase, pyruvate dehydrogenase complex, citrate synthase, aconitase, alpha-ketoglutarate dehydrogenase, glutamate dehydrogenase, and NADH oxidase.

Animals↗

PubMed1995

Effect of substrate and cell surface hydrophobicity on phosphate utilization in bacteria.

We measured the rates of utilization of hydrophobic and hydrophilic phosphate compounds in gram-negative bacteria with different surface hydrophobicities, isolated from wetland habitats. Three hydrophobic and two hydrophilic bacterial species were selected for study by measuring cell adherence to hydrocarbons. The bacteria were grown under phosphorus-limited conditions with P(infi), hydrophilic (beta)-glycerophosphate, or hydrophobic phosphatidic acid as the phosphate source. Hydrophilic bacteria grew most rapidly on P(infi), followed by (beta)-glycerophosphate. Phosphatidic acid did not support growth or did so at a much later time (40 h) than did the other phosphate treatments. Although all hydrophobic species grew well on these substrates, the rate of growth of two Acinetobacter baumannii isolates on phosphatidic acid exceeded the rate of growth on phosphate or (beta)-glycerophosphate. A membrane phospholipid and lipopolysaccharide were used as a source of phosphorus by hydrophobic species, whereas hydrophilic species could not use the membrane phospholipids and used lipopolysaccharide to a lesser extent. Besides hydrophobic interaction between cells and substrate, phosphatase activity, which was cell bound in hydrophilic species but 30 to 50% unbound in hydrophobic species, affected cell growth. Dialyzed culture supernatant containing phosphatase from hydrophobic species increased the phosphate availability to hydrophilic species. Additionally, cellular extracts from a hydrophilic species, when added to hydrophilic cells, permitted growth on hydrophobic phosphate sources. Naturally occurring amphiphilic humic acids affected the utilization of P(infi) and (beta)-glycerophosphate in bacteria with hydrophilic surfaces but did not affect hydrophobic bacteria. Our results indicate that hydrophobic phosphate sources can be used by bacteria isolated from aquatic environments as the sole phosphorus source for growth. This utilization, in part, appears to be related to cell surface hydrophobicity and extracellular enzyme production.

Journal Article↗

PubMed1969

Effects of some antitumor agents on growth and glycolytic enzymes of the flagellate Crithidia.

Some antitumor agents known to specifically inhibit certain tumor cell enzymes were examined for activity against glycolytic enzymes and growth of the insect trypanosomatid, Crithidia fasciculata. The cytoplasmic enzymes hexokinase, alpha-glycerophosphate dehydrogenase, malic dehydrogenase, and glucose-6-phosphate dehydrogenase were tested. Agaricic acid (2-hydroxy-1,2,3-nonadecane tricarboxylic acid) was highly inhibitory (50 to 100%) to malic and alpha-glycerophosphate dehydrogenases at approximately 3 x 10(-5)m; 2-(p-hydroxyphenyl)-2-phenylpropane (2 x 10(-4)m), and 5,6-dichloro-2-benzoxazolinone (5 x 10(-4)m) were less effective (50% inhibition) against them. The antiprotozoal agents primaquine (4 x 10(-4)m) and Melarsoprol (8 x 10(-4)m) were 30 to 40% inhibitory. Agaricic acid, 2-(p-hydroxyphenyl)-2-phenylpropane, and 5,6-dichloro-2-benzoxazolinone inhibited growth of Crithidia at less than 10(-4)m. Eight other test compounds from the Cancer Chemotherapy National Service Center (CCNSC) were not toxic to cell growth, although two (4-biphenylcarboxylic acid and 1-[p-chlorobenzyl]-2-ethyl-5-methyl-indole-3-acetic acid) inhibited Crithidia alpha-glycerophosphate dehydrogenase below 1 mm. All of the compounds used specifically inhibited cancer cell alpha-glycerophosphate dehydrogenase. The corresponding enzyme in pathogenic African trypanosomes is important in their terminal respiration. C. fasciculata may be useful in preliminary evaluation of chemotherapeutic agents as potential trypanocides.

Acetates↗

PubMed1984

Thyroid hormones augment catecholamine-stimulated brown adipose tissue thermogenesis in the ovine fetus.

The effects of exogenous changes in thyroid status on in vitro brown adipose tissue (BAT) cellular respiration and thermogenic enzymes (sodium-potassium ATP' ase and alpha-glycerophosphate dehydrogenase) were studied in fetal sheep. Thyroidectomy and insertion of a constant infusion pump followed by 8 days of infusion of either T3 (n = 7) or vehicle (n = 4) were performed in fetal lambs at 119-121 days gestation. The animals were then killed, and perirenal BAT was removed for study. T3 infusion resulted in a mean plasma T3 concentration of 322 +/- 52 ng/dl compared to levels at the limits of detection (9 ng/dl) in the vehicle-infused animals. Basal respiration values with or without ouabain were similar in the two groups. Maximum mean norepinephrine (NE; 10(-6) M)-stimulated respiration (110.2 +/- 11.6 microliter O2/10(6) cells X h) in the T3-treated group was greater than stimulated mean respiration (55.3 +/- 15.6 microliter O2/10(6) cells X h) in the untreated animals (P less than 0.02). NE-stimulated respiration in the presence of ouabain (i.e. nonsodium transport-dependent respiration) was increased in the T3-treated animals (P less than 0.01), while sodium transport-dependent respiration was not different. (Bu)2cAMP-stimulated respiration was greater in the T3-treated group (P less than 0.001), while alpha-glycerophosphate substrate respiration was not different. Mitochondrial alpha-glycerophosphate dehydrogenase and Na-K-ATPase activities were similar. These studies demonstrate that BAT catecholamine-stimulated respiration is influenced by thyroid status in the ovine fetus. The increase in both NE- and (Bu)2cAMP-stimulated respiration suggests a postreceptor effect on intracellular metabolism, though an effect on beta-adrenergic receptors also might have occurred. Neither sodium transport (NA-K-ATPase)-dependent respiration nor mitochondrial alpha-glycerophosphate dehydrogenase appear to be involved. These data suggest that the relative hyperthyroid state that occurs in the newborn of both man and sheep may be important through its effects on BAT metabolism to insure adequate temperature regulation during neonatal adaptation.

Adipose Tissue, Brown↗

PubMed1991

Triiodothyronine and insulin effects on malic enzyme in hypothyroid and diabetic rats.

We examined the effects of T3 and insulin on the activity of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme in control, thyroidectomized, thyroidectomized food-restricted, and thyroidectomized diabetic rats. In the three untreated thyroidectomized groups, the decrease in hepatic nuclear T3 content was accompanied by a marked reduction in the levels of alpha-glycerophosphate dehydrogenase and malic enzyme activity. Although the levels of both enzymes were increased by a receptor-saturating dose of T3, the alpha-glycerophosphate dehydrogenase response in the thyroidectomized groups was almost identical to that in controls, whereas that of malic enzyme was reduced to 45-62% of control values. Insulin failed to stimulate the alpha-glycerophosphate dehydrogenase levels in untreated and T3-treated thyroidectomized groups, but caused an increase in malic enzyme activity by 79-130% in untreated thyroidectomized groups, and enhanced the activity of this enzyme to about twice that seen with T3 alone. These effects were independent of changes in nuclear T3 binding parameters. The data suggest that insulin may act on malic enzyme synthesis through its general stimulatory effect on protein synthesis, or by antagonizing factors that inhibit the induction of this enzyme.

Animals↗

PubMed1986

[Phospholipid biosynthesis in the lungs in a chronic inflammatory bronchopulmonary process].

Glycerokinase, glycerophosphate dehydrogenase, glycerophosphate acyltransferase activity, glycerophosphate, dioxiacetonphosphate level and in vivo incorporation of (U-14C)-glucose into the lung phospholipid structure were studied in normal rats and in conditions of chronic bronchopulmonary inflammation. The inhibition of glycerokinase and glycolytic ways of glycerophosphate formation was demonstrated. The data obtained have shown that glucose incorporation into phosphatidyl cholines, phosphatidyl glycerols and phosphatidyl ethanolamines was decreased, while the incorporation of radioactivity into the sphingomyelins and lysophosphatidyl cholines was significantly activated.

Animals↗

PubMed1977

Oxidative phosphorylation in mitochondria from different fiber types of chicken muscles.

Isolated mitochondria from different types of muscle fibers from chickens 3 to 5 weeks were studied to evaluate the comparative oxidation of various substrates. Pectoralis (alphaW fibers), lateral adductor (betaR fibers), and medial adductor (alphaR fibers) were the muscles used. Oxygen consumption rates, RCR, and ADP/O ratios were measured to study mitochondrial function. Mitochondria from pectoralis muscle utilized pyruvate, succinate, L-glutamate, alpha-glycerophosphate, and beta-hydroxybutyrate. Mitochondria from the other two muscle types utilized all of those substrates except alpha-glycerophosphate. In each muscle type utilization of NADH was minimum and was not coupled with phosphorylation of ADP. Thus, in alphaW muscles oxidation of alpha-glycerophosphate may play an important role in transport of cytoplasmic NADH to the mitochondrial respiratory chain. In alphaR and betaR muscles "shuttle" systems other than alpha-glycerophosphate oxidation, e.g., beta-hydroxybutyrate, may perform that important role.

Animals↗

PubMed1984

Ion-transporting ATPases and matrix mineralization in cultured osteoblastlike cells.

Cultures of osteoblastlike cells obtained from the endosteal surfaces of rabbit long bones formed and mineralized an extracellular matrix when they were supplied daily with medium containing fresh ascorbate. No matrix formed without this supplementation. The matrix mineralized whether or not beta-glycerophosphate, a substrate of alkaline phosphatase, was added to the medium. The ion-transporting ATPase activities of untreated, ascorbate-treated, and ascorbate plus beta-glycerophosphate-treated cells were measured. Ascorbate-treated and ascorbate plus beta-glycerophosphate-treated cells had similar enzyme activities. The activities of the Ca2+-ATPase; Ca2+,Mg2+-ATPase; and alkaline phosphatase in treated cells were elevated over the activities in untreated cells. Na+,K+-ATPase activity was lower in treated than in untreated cells. HCO3--ATPase activity was not changed by treatment. Alkaline phosphatase activity was 20 times higher in freshly isolated osteoblastlike cells than in cells grown to confluence in primary culture. In addition, subculturing further reduced the activity of this osteoblast-marker enzyme. The activities of the ion-transporting ATPases and alkaline phosphatase in second passage cells were similar to the activities of these enzymes in fresh, noncalcifying tissues. Nevertheless, second passage cells retain the ability to mineralize an extracellular matrix, and their ion-transporting ATPase and alkaline phosphatase activities are altered when the cells mineralize a matrix.

Adenosine Triphosphatases↗

PubMed2000

Indolic constituents and indole-3-acetic acid biosynthesis in the wild-type and a tryptophan auxotroph mutant of Arabidopsis thaliana.

The tryptophan auxotroph mutant trp3-1 of Arabidopsis thaliana (L.) Heynh., despite having reduced levels of L-tryptophan, accumulates the tryptophan-derived glucosinolate, glucobrassicin and, thus, does not appear to be tryptophan-limited. However, due to the block in tryptophan synthase, the mutant hyperaccumulates the precursor indole-3-glycerophosphate (up to 10 mg per g FW). Instability of indole-3-glycerophosphate leads to release of indole-3-acetic acid (IAA) from this metabolite during standard workup of samples for determination of conjugated IAA. The apparent increase in "conjugated IAA" in trp3-1 mutant plants can be traced back entirely to indole-3-glycerophosphate degradation. Thus, the levels of neither free IAA nor conjugated IAA increase detectably in the trp3-1 mutant compared to wild-type plants. Precursor-feeding experiments to shoots of sterile-grown wild-type plants using [2H]5-L-tryptophan have shown incorporation of label from this precursor into indole-3-acetonitrile and indole-3-acetic acid with very little isotope dilution. It is concluded that Arabidopsis thaliana shoots synthesize IAA from L-tryptophan and that the non-tryptophan pathway is probably an artifact.

Arabidopsis↗

PubMed1977

Role of quinones in electron transport to oxygen and nitrate in Escherichia coli. Studies with a ubiA- menA- double quinone mutant.

A ubiA- menA- double quinone mutant of Escherichia coli K12 was constructed together with other isogenic strains lacking either ubiquinone or menaquinone. These strains were used to study the role of quinones in electron transport to oxygen and nitrate. Each of the four oxidases examined (NADH, D-lactate, alpha-glycerophosphate and succinate) required a quinone for activity. Ubiquinone was active in each oxidase system while menaquinone gave full activity in alpha-glycerophosphate oxidase, partial activity in D-lactate oxidase but was inactive in NADH and succinate oxidation. The aerobic growth rates, growth yields and products of glucose metabolism of the quinone-deficient strains were also examined. The growth rate and growth yield of the ubi+menA- strain was the same as the wild-type strain, whereas the ubiA-men+ strain grew more slowly on glucose, had a lower growth yield (30% of wild type) and accumulated relatively large quantities of acetate and lactate. The growth of the ubiA-menA- strain was even more severely affected than that of the ubiA-men+ strain. Electron transport from formate, D-lactate, alpha-glycerophosphate and NADH to nitrate was also highly dependent on the presence of a quinone. Either ubiquinone or menaquinone was active in electron transport from formate and the activity of the quinones in electron transport from the other substrates was the same as for the oxidase systems. In contrast, quinones were not obligatory carriers in the anaerobic formate hydrogenlyase system. It is concluded that the quinones serve to link the various dehydrogenases with the terminal electron transport systems to oxygen and nitrate and that the dehydrogenases possess a degree of selectivity with respect to the quinone acceptors.

Aerobiosis↗

PubMed1983

Increased lipid content in the rat axotomized superior cervical ganglion.

Transection of postganglionic nerves of the rat superior cervical ganglion results in significant increases in the concentration of lipid as well as the total content of lipid in the ganglion. The purpose of this work was to characterize the effect of axotomy on the major classes of lipid in the ganglion and to examine possible relationships among increases in lipid content and changes in steady-state concentrations of metabolites utilized in lipid biosynthesis. Major classes of lipids in axotomized and contralateral intact ganglia were compared using the Folch extraction and partitioning scheme. Analyses of lipids were carried out 7 days after axotomy because total lipid content was increased maximally at that time. The increase in lipid content in axotomized ganglia was related primarily to an increase in phospholipids. Amounts of gangliosides, cerebrosides, cholesterol, and proteolipid protein did not change significantly after axotomy. The elevation of phospholipid content was accompanied by increases in steady-state concentrations of alpha-glycerophosphate and decreases in Coenzyme A in the ganglion; however, concentrations of acetyl CoA and long-chain acyl CoA compounds did not change significantly in axotomized ganglia. Increases in alpha-glycerophosphate do not appear to arise from enhanced utilization of glucose because alpha-glycerophosphate dehydrogenase activity was decreased in axotomized ganglia and the incorporation of [U-14C] glucose into lipids in explants of the axotomized ganglia in vitro was not elevated. In contrast, incorporation of [U-14C] glycerol into lipids of explants from axotomized ganglia was increased in vitro. The results suggest that utilization of extracellular glycerol for phospholipid biosynthesis may be enhanced in the rat's axotomized superior cervical ganglion.

Animals↗

PubMed1975

Ragged-red fibers. A biochemical and morphological study.

Histochemical, ultrastructural and biochemical studies were performed on muscle biopsy specimens from a 30-year-old man with proximal limb weakness. Modified Gomori trichome stains of anterior tibial muscle revealed accumulations of red-staining material in the subsarcolemmal and intermyofibrillar regions of virtually every fiber (ragged-red fibers); these accumulations were rich in oxidative enzymes. Electron microscopy of this muscle showed that the red-staining areas consisted of large collections of abnormal-appearing mitochondria. Mitochondria isolated from the quadriceps muscle showed lack of respiratory control with alpha-glycerophosphate as substrate. However, the lack of respiratory control with alpha-glycerophosphate must be interpreted with caution since the quadriceps muscle was severely degenerated, and biochemical alterations of mitochondria may occur secondary to muscle degeneration itself. Nevertheless, this is the second reported case of lack of respiratory control with alpha-glycerophosphate in a patient with ragged-red fibers. Further interpretation of this defect and its significance must await more studies to determine whether this muscle mitochondrial abnormality is a common finding in the disorders in which ragged-red fibers are encountered.

Adenosine Triphosphatases↗

PubMed1989

Expression of the chondrogenic phenotype by mineralizing cultures of embryonic chick calvarial bone cells.

Cells released by sequential enzymatic digestion of 18-day chick calvariae were cultured over a 4-5 week period in Alpha modified Eagles medium. In some cultures the medium was supplemented with ascorbate and/or Na-beta-glycerophosphate. Microscopic examination of these cultures showed both polygonal and spindle-shaped cells. The biochemical nature of these cells was investigated by incubating the cultures with radiolabelled proline and subsequently analysing the medium and cell layer proteins by SDS/PAGE and fluorography. Osteoblast and chondrocyte-containing cultures were clearly distinguished in this way as the former cells secreted type I collagen while the latter secreted types II and X collagens as the major medium macromolecules. Type X collagen synthesis occurred after 14 days, but only in cultures supplemented with both ascorbate and Na-beta-glycerophosphate, and was maintained for the duration of the culture period. Unsupplemented cultures and those containing either ascorbate alone or Na-beta-glycerophosphate alone failed to synthesize type X collagen after 28 days. Isolated cells pulsed with radiolabelled proline at confluence and organ cultures of embryonic chick calvaria synthesized types I and V collagens only. These data demonstrate that the expression of phenotype by heterogeneous populations of bone cells could be modulated by a combination of culture conditions including the length of time in culture and conditions favourable for the formation of a mineralized matrix.

Animals↗