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At least 73 records · Page 4Linked to original sources
PubMed1986

Localization of alkaline phosphatase activity at microbody membranes of Neurospora crassa and Aspergillus nidulans.

Hyphal cells of Neurospora crassa and Aspergillus nidulans, grown in Sabouraud glucose broth or in a defined medium with xanthine or its catabolites as the nitrogen source, contained single membrane-bound organelles cytochemically identified as microbodies. Modified Gomori procedures at the ultrastructural level revealed putative alkaline phosphatase activity sites in thin sections of cells of both species of fungi. Microbody membranes displayed electron opaque deposits (lead phosphate) which were absent in control preparations either lacking the substrate (beta-glycerophosphate) or the lead capture ion. Inhibition of this enzymic activity was achieved in parallel incubations fortified with the inhibitor levamisole. Cells grown in media containing limiting levels of inorganic phosphate revealed additional alkaline phosphatase activity at and along the nuclear membrane and endoplasmic cisternae. Hexagonal inclusions found in the cytoplasm of N. crassa (but not A. nidulans) and believed to arise from microbody precursors were without demonstrable cytochemical staining for microbody marker oxidases.

Alkaline Phosphatase↗
PubMed1966

The nucleoids of rat liver cell microbodies. Fine structure and enzymes.

The nucleoids of microbodies of rat liver cells were isolated in a highly homogeneous and pure state, by treating the microbody-rich fraction, prepared from 10% polyvinylpyrrolidone-0.25 M sucrose homogenate, with Triton X-100. Three treatments with 0.1% detergent were enough to render the nucleoids free from contamination with mitochondria, microsomes, lysosomes, and intact microbodies. Electron microscopically, the nucleoids were found to consist of parallel bundles of highly dense hollow tubules, the outer and inner diameters of which are approximately 150 and 50 A, respectively. Ten tubules are arranged around a longitudinal space 190 x 200 A in width. The nucleoids thus show a honeycomb appearance in the cross-plane and a parallel-packed structure in the longitudinal plane. Biochemically, the nucleoids were found to bear only urate oxidase among probably microbody-enzymes, and they might be the only cytoplasmic particles of rat liver cells in which the enzyme locates. Urate oxidase activity, on a unit protein basis, of the nucleoid preparation is approximately 380 times as high as that of the whole homogenate, and is almost comparable with that of a commercial type I enzyme preparation. No enzymes of mitochondrial, microsomal, and lysosomal origins were detected in the nucleoids. The fine structure of the nucleoids is described in detail, and a probable schematic diagram is presented.

Animals↗
PubMed1975

Glycolate oxidase content of microbodies as affected by nitrate.

Glycolate oxidase is loosely held by microbodies obtained from etiolated barley (Hordeum vulgare L.) leaves depleted of nitrate. Defined centrifugation conditions cause the complete detachment of the enzyme from the microbodies. Addition of nitrate to these plants brings about a greater retention of glycolate oxidase by the microbodies. Synthesis of a nitrate-induced protein seems to be responsible for the enhanced retention of glycolate oxidase. Catalase, on the contrary, is strongly attached to the microbodies under all nutritional and experimental conditions considered.

Journal Article↗
PubMed1977

Effects of Indoleacetic Acid on the Quantity of Mitochondria, Microbodies, and Plastids in the Apical and Expanding Cells of Dark-grown Oat Coleoptiles.

We determined the number of mitochondria, microbodies, and plastids in dark-grown oat (Avena sativa) coleoptiles following incubation in indoleacetic acid (IAA) for a period of 60 minutes at 6-minute intervals. In the apical outer epidermis of coleoptiles, the mitochondria increased from 31.4 to 35 per cell section with a 6-minute incubation in IAA, and this trend persisted over the 60-minute incubation. Neither the microbodies, plastids, nor the dicytosomes (Gawlik and Miller 1974 Plant Physiol 54:217-221) responded to the hormone. The apical parenchyma showed no change in quantity of any of the organelles including the dictyosomes during IAA incubation. The quick response of mitochondria in the coleoptile tip could be interpreted as an association of this organelle with hormone transport, growth, or perhaps with gravity perception. In the subapical expansion region, IAA caused significant reductions of mitochondria, microbodies, and dictyosomes in the outer epidermis compared to the control, the timing of which preceded the IAA-induced elongation and of geotropism. The fast response of organelles in the various cells is probably a change in organelle volume rather than number. That microbodies show a response to the plant hormone in the permanently achlorophyllous epidermis indicates that these organelles, in addition to their peroxisomal functions in green leaves, also may have a growth regulation function. IAA treatment was without effect on the quantity of the various types of plastids (including the amyloplasts) in the different oat coleoptile cells.

Journal Article↗
PubMed1980

Density of Microbodies on Sucrose Gradients during Phytochrome-mediated Glyoxysome Peroxisome Transformation in Cotyledons of Mustard Seedlings.

The microbodies extracted from the cotyledons of mustard seedlings (Sinapis alba L.) form two bands (at 1.18 kilograms per liter together with the mitochondria, and at 1.24 kilograms per liter) on conventional isopycnic sedimentation density gradients. The artifactual co-banding of part of the microbodies with the mitochondria can be prevented by using flotation gradients. Using this procedure, a systematic investigation revealed no effect of seedling age and irradiation (far red or white light) on the density of the microbody population (1.242 +/- 0.002 kilograms per liter). Thus, although light, through phytochrome, induces conspicuous changes in their enzyme composition the microbodies appear as a homogeneous population of constant density on a sucrose gradient.

Journal Article↗
PubMed1986

Characterization of the gene for the microbody (glycosomal) triosephosphate isomerase of Trypanosoma brucei.

To determine how microbody enzymes enter microbodies, we are studying the genes for glycosomal (microbody) enzymes in Trypanosoma brucei. Here we present our results for triosephosphate isomerase (TIM), which is found exclusively in the glycosome. We found a single TIM gene without introns, having one major polyadenylated transcript of 1500 nucleotides with a long untranslated tail of approximately 600 nucleotides. By a novel method, suitable for low abundance transcripts, we demonstrate that TIM mRNA contains the 35-nucleotide leader sequence (mini-exon) also found on several other trypanosome mRNAs. The TIM gene and a DNA segment of at least 6 kbp upstream of the gene are transcribed at an equal rate in isolated nuclei, suggesting that the gene is part of a much larger transcription unit. The predicted protein is of the same size as TIMs from other organisms and shares approximately 50% amino acid homology with other eukaryote TIMs, somewhat less with prokaryote TIMs. Trypanosome TIM is the most basic of all TIMs sequenced thus far. This is, in part, due to the presence of two clusters of positively charged residues in the molecule which may act as a signal for entry into glycosomes.

Amino Acid Sequence↗
PubMed1985

Development of fate of electron-dense microbodies in trap cells of the nematophagous fungus Arthrobotrys oligospora.

The development of electron-dense microbodies in cells of capture organs of the nematophagous fungus Arthrobotrys oligospora was studied with different ultrastructural techniques. Kinetic experiments revealed that the synthesis of these microbodies started in a very early stage of trap formation; the organelles originated from special regions of endoplasmic reticulum by budding. Mature organelles were surrounded by a single membrane of approximately 9 nm (KMnO4-fixation) and lacked crystalline inclusions. The presence of the electron-dense microbodies was independent of the conditions during which the traps had developed. The organelles remained intact during aging of the trap cells. They were also observed in the trophic hyphae after capture and penetration of nematodes. However, the distribution patterns of these organelles in the trophic hyphae, which were identical to those observed after germination of isolated traps on different cultivation media, suggested that their presence must be explained by dilution of organelles in newly formed cells.

Animals↗
PubMed1991

A phosphoglycerate kinase-like molecule localized to glycosomal microbodies: evidence that the topogenic signal is not at the C-terminus.

The phosphoglycerate kinase (PGK) gene complex of Trypanosoma brucei contains three tandemly linked related genes. One gene encodes a cytoplasmic PGK, while another encodes a PGK isozyme localized to glycosomal microbodies. In this communication, we report that the third gene in this complex encodes a 56-kDa molecule which is also localized to the glycosomal core. DNA sequence analysis indicates that this gene contains multiple substitutions and a large insertion in the amino domain, but that it is very similar to the other PGK isozymes in the carboxy domain. The C-terminal tripeptide is identical to that of the cytoplasmic isozyme, and only one conservative change occurs in the last 25 amino acids. The encoded protein, p56, thus contrasts with the many peroxisomal microbody proteins in which the C-terminal tripeptide contains sufficient information for targeting to peroxisomes. Multiple mechanisms may exist for targeting proteins to the protein cores of microbody organelles. Comparisons of the DNA sequences of several alleles suggest that homologous recombination plays a role in the generation of allelic diversity.

Alleles↗
PubMed1991

Physiological studies on the utilization of oleic acid by Saccharomyces cerevisiae in relation to microbody development.

We studied the influence of specific growth conditions on the induction of beta-oxidation enzymes and rate of microbody proliferation in S. cerevisiae by oleic acid. Of all conditions tested, highest enzyme levels and microbody numbers were achieved in glucose-limited continuous cultures, supplemented with oleic acids second carbon source. Comparable enzyme levels were observed in identical cultures of peroxisome-deficient (pas) mutants of S. cerevisiae. These experiments showed chemostat cultures on glucose/oleic acid mixtures to be a method of choice for future studies on microbody biogenesis/assembly in constructed, conditional pas mutants.

Cell Division↗
PubMed2004

Penicillium chrysogenum Pex5p mediates differential sorting of PTS1 proteins to microbodies of the methylotrophic yeast Hansenula polymorpha.

We have isolated the Penicillium chrysogenum pex5 gene encoding the receptor for microbody matrix proteins containing a type 1 peroxisomal targeting signal (PTS1). Pc-pex5 contains 2 introns and encodes a protein of approximately 75 kDa. P. chrysogenum pex5 disruptants appear to be highly unstable, show poor growth, and are unable to sporulate asexually. Furthermore, pex5 cells mislocalize a fluorescent PTS1 reporter protein to the cytosol. Pc-pex5 was expressed in a PEX5 null mutant of the yeast Hansenula polymorpha. Detailed analysis demonstrated that the PTS1 proteins dihydroxyacetone synthase and catalase were almost fully imported into microbodies. Surprisingly, alcohol oxidase, which also depends on Pex5p for import into microbodies, remained mainly in the cytosol. Thus, P. chrysogenum Pex5p has a different specificity of cargo recognition than its H. polymorpha counterpart. This was also suggested by the observation that Pc-Pex5p sorted a reporter protein fused to various functional PTS1 signals with different efficiencies.

Alcohol Oxidoreductases↗
PubMed1996

Transport of chimeric proteins that contain a carboxy-terminal targeting signal into plant microbodies.

Malate synthase is a glyoxysome-specific enzyme. The carboxy-terminal tripeptide of the enzyme is Ser-Arg-Leu (SRL), which is known to function as a peroxisomal targeting signal in mammalian cells. To analyze the function of the carboxy-terminal amino acids of pumpkin malate synthase in plant cells, a chimeric gene was constructed that encoded a fusion protein which consisted of beta-glucuronidase and the carboxyl terminus of the enzyme. The fusion protein was expressed and accumulated in transgenic Arabidopsis that had been transformed with the chimeric gene. Immunocytochemical analysis of the transgenic plants revealed that the carboxy-terminal five amino acids of pumpkin malate synthase were sufficient for transport of the fusion protein into glyoxysomes in etiolated cotyledons, into leaf peroxisomes in green cotyledons and in mature leaves, and into unspecialized microbodies in roots, although the fusion protein was no longer transported into microbodies when SRL at the carboxyl terminus was deleted. Transport of proteins into glyoxysomes and leaf peroxisomes was also observed when the carboxy-terminal amino acids of the fusion protein were changed from SRL to SKL, SRM, ARL or PRL. The results suggest that tripeptides with S, A or P at the -3 position, K or R at the -2 position, and L or M at the carboxyl terminal position can function as a targeting signal for three kinds of plant microbody.

Amino Acid Sequence↗
PubMed1956

Microbodies and the problem of mitochondrial regeneration in liver cells.

The cytoplasm of the hepatic cell contains, besides the well known organelles, microbodies, characterized by a single membrane, a finely granular matrix, and average dimensions below those of mitochondria. Microbodies, rare in normal cells, become more numerous in regenerative livers and in various pathological conditions. In these cases, they either evolve towards degenerative forms or else show structural modifications corresponding to transitional forms between them and mitochondria. This suggests to us that the microbodies can be precursors of mitochondria.

Cytoplasm↗
PubMed1997

Hydroxypyruvate reductase with a carboxy-terminal targeting signal to microbodies is expressed in Arabidopsis.

Five Arabidopsis EST cDNA clones of hydroxypyruvate reductase (HPR), a photorespiratory enzyme in leaf peroxisomes, were sequenced. Deduced amino acid sequences revealed that HPR in Arabidopsis contained the carboxy-terminal targeting signal to microbodies. Nucleotide sequence analysis showed that the cDNA with the longest insert contained an open reading frame of 1,158 bp which encoded a polypeptide with 386 amino acids with a calculated molecular mass of 42,251 Da. A Southern blot analysis suggested that the Arabidopsis HPR gene, like that of the pumpkin HPR gene, exists as a single copy. Two kinds of pumpkin HPR mRNA might be produced from a single gene by alternative splicing, but the structure of the genomic DNA indicated that the Arabidopsis HPR gene did not undergo alternative splicing. We detected a polypeptide with a molecular mass of 42 kDa in green leaves of Arabidopsis using an HPR-specific antibody. Immunoelectron microscopy revealed that Arabidopsis HPR protein was exclusively localized in leaf peroxisomes in green leaves. These results indicate that HPR is expressed in a form with a carboxy-terminal targeting signal to microbodies and is localized in microbodies in Arabidopsis, suggesting that the differences in the gene structure and the regulation of gene expression of HPR are probably due to species-specific differences in plants.

Alcohol Oxidoreductases↗
PubMed1974

Microbodies (peroxisomes) containing catalase in myocardium: morphological and biochemical evidence.

Microbodies characterized by a single limiting membrane and finely granular matrix occur in mouse myocardium and appear in close spatial relation to mitochondria and sarcoplasmic reticulum. The presence of catalase in the microbodies is revealed cytochemically and confirmed biochemically by direct measurement of its activity in myocardial tissue fractions. It is suggested that the microbodies may play an important role in myocardial lipid metabolism.

Animals↗
PubMed2002

Compartmentation of enzymes in a microbody, the glycosome, is essential in Trypanosoma brucei.

All kinetoplastids contain membrane-bound microbodies known as glycosomes, in which several metabolic pathways including part of glycolysis are compartmentalized. Peroxin 2 is essential for the import of many proteins into the microbodies of yeasts and mammals. The PEX2 gene of Trypanosoma brucei was identified and its expression was silenced by means of tetracycline-inducible RNA interference. Bloodstream-form trypanosomes, which rely exclusively on glycolysis for ATP generation, died rapidly upon PEX2 depletion. Insect-form (procyclic) trypanosomes do not rely solely on glycolysis for ATP synthesis. PEX2 depletion in procyclic forms resulted in relocation of most tested matrix proteins to the cytosol, and these mutants also died. Compartmentation of microbody enzymes is therefore essential for survival of bloodstream and procyclic T. brucei. In contrast, yeasts and cultured mammalian cells grow normally in the absence of peroxisomal membranes unless placed on selective media.

Animals↗
PubMed1996

Functional transformation of microbodies in higher plant cells.

In germinating fatty seedlings, microbodies are functionally transformed to leaf peroxisomes from glyoxysomes during greening, and then converted to glyoxysomes from leaf peroxisomes during senescence. Immunocytochemical studies revealed that glyoxysomes can exchange directly into leaf peroxisomes during greening and leaf peroxisomes are once again directly converted to glyoxysomes during senescence. The reversible transformations of microbodies are regulated at various levels, such as gene expression, splicing of the mRNA and degradation of microbody proteins. The regulatory mechanisms underlying this organelle differentiation are described.

Biological Transport↗
PubMed1976

Plant microbody proteins, III. Labelling of the peroxisomal membrane protein SP-63 in vitro and in vivo.

Methods were developed to charcterize membranes and membrane components of leaf peroxisomes from Lens culinaris. While microbodies from etiolated young leaves exhibited an equilibrium density of 1.19 g/cm3, older leaves or leaves exposed to light for increasing periods of time contained microbodies banding at higher densities up to 1.235 g/cm3. Similar values were also found for the corresponding microbody membranes, which could be labelled with diazotized [35S]sulphanilic acid. Labelling was also performed using proteins extracted from the membranes. Their main structural protein (SP-63) was solubilized with sodium dodecylsulphate and labelled with fluorescent compounds as well as with diazotized [35S]sulphanilic acid or [3H]iodoacetic acid. These conversions greatly facilitate all analytical procedures, e.g. tracing the migration of SP-63 in gels or the movement in sucrose gradients containing sodium dodecylsulphate during zonal centrifugation. Also, labelling of SP-63 in vivo was accomplished when labelled amino acids were infused into etiolated leaves while exposing them to light.

Darkness↗
PubMed2006

Yeast and filamentous fungi as model organisms in microbody research.

Yeast and filamentous fungi are important model organisms in microbody research. The value of these organisms as models for higher eukaryotes is underscored by the observation that the principles of various aspects of microbody biology are strongly conserved from lower to higher eukaryotes. This has allowed to resolve various peroxisome-related functions, including peroxisome biogenesis disorders in man. This paper summarizes the major advances in microbody research using fungal systems and specifies specific properties and advantages/disadvantages of the major model organisms currently in use.

Mitosporic Fungi↗