Studies on peroxisomes. VI. Relationship between the peroxisomal core and urate oxidase

The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1

Peroxisomes are ubiquitous eukaryotic organelles with the primary role of breaking down very long- and branched-chain fatty acids for subsequent β-oxidation in the mitochondrion. Like mitochondria, peroxisomes are major sites for oxygen utilization and potential contributors to cellular oxidative stress. The accumulation of oxidatively damaged proteins, which often develop into inclusion bodies (of oxidized, aggregated, and cross-linked proteins) within both mitochondria and peroxisomes, results in loss of organelle function that may contribute to the aging process. Both organelles possess an isoform of the Lon protease that is responsible for degrading proteins damaged by oxidation. While the importance of mitochondrial Lon (LonP1) in relation to oxidative stress and aging has been established, little is known regarding the role of LonP2 and aging-related changes in the peroxisome. Recently, peroxisome dysfunction has been associated with aging-related diseases indicating that peroxisome maintenance is a critical component of 'healthy aging'. Although mitochondria and peroxisomes are both needed for fatty acid metabolism, little work has focused on understanding the relationship between these two organelles including how age-dependent changes in one organelle may be detrimental for the other. Herein, we summarize findings that establish proteolytic degradation of damaged proteins by the Lon protease as a vital mechanism to maintain protein homeostasis within the peroxisome. Due to the metabolic coordination between peroxisomes and mitochondria, understanding the role of Lon in the aging peroxisome may help to elucidate cellular causes for both peroxisome and mitochondrial dysfunction.

Rat urate oxidase produced by recombinant baculovirus expression: formation of peroxisome crystalloid core-like structures

Urate oxidase (EC 1.7.3.3), which catalyzes the oxidation of uric acid to allantoin, is present in most mammals but absent in humans and hominoid primates. In rats and most other mammals that catabolize uric acid to allantoin, this enzyme is localized within the crystalloid cores of peroxisomes present in liver parenchymal cells. To determine whether urate oxidase forms these crystalloid cores or whether core-forming protein(s) exist in association with urate oxidase, a baculovirus expression vector system was used to overproduce the full-length rat urate oxidase in Spodoptera frugiperda cells. Urate oxidase was expressed to a level of approximately 30% of the total protein in this system. Immunoblot analysis demonstrated that the baculovirus-generated protein had electrophoretic and immunologic properties similar to those of urate oxidase expressed in rat liver. Immunofluorescence and electron microscopic examination revealed that the overexpressed recombinant urate oxidase is present in both the cytoplasm and the nucleus of infected insect cells as numerous 1- to 3-microns discrete particles. These insoluble protein aggregates, which were positively stained for urate oxidase by protein A-gold immunocytochemical approach, did not appear to be delimited by a single membrane. They revealed a crystalloid structure reminiscent of rat peroxisomal core consisting of bundles of tubules with an inner diameter of approximately 50 A. The recombinant urate oxidase particles, isolated by a single-step procedure, were composed entirely of 35-kDa urate oxidase subunit. These studies indicate that rat urate oxidase is capable of forming insoluble crystalloid core-like structures.

Peroxisomal enzymes in normal and tumoral human breast

The presence of peroxisomes and their enzymatic content were investigated and compared in healthy and neoplastic human breast epithelial cells using cytochemical studies at the ultrastructural level as well as Western blot and biochemical analyses. Ultrastructural cytochemistry revealed the presence of these organelles in both normal and neoplastic breast tissues. Their mean diameter was 0.27 +/- 0.11 micron. No significant difference was noted between numbers of peroxisomes in normal and neoplastic breast epithelia. Catalase, D-amino acid oxidase, and urate oxidase were found to be expressed in mammary carcinoma and in surrounding non-malignant tissue when the postnuclear supernatant fractions prepared from homogenates were assessed by Western blot techniques. Their specific activities and that of fatty acyl CoA oxidase as determined spectrophotometrically were found to be diminished in the tumour when compared with the control tissue. On the other hand, no significant difference was found in the specific activity of the L-alpha-hydroxy acid oxidase of normal and neoplastic human breast tissues. Investigations of the relationship between peroxisomal enzymes and tumour grade revealed that catalase, urate oxidase, and fatty acyl CoA oxidase activities in breast neoplastic tissues belonging to grade III were significantly lower than in the adjacent normal tissues.

Molecular characterization of the Drosophila melanogaster urate oxidase gene, an ecdysone-repressible gene expressed only in the malpighian tubules

The urate oxidase (UO) gene of Drosophila melanogaster is expressed during the third-instar larval and adult stages, exclusively within a subset of cells of the Malpighian tubules. The UO gene contains a 69-base-pair intron and encodes mature mRNAs of 1,224, 1,227, and 1,244 nucleotides, depending on the site of 3' endonucleolytic cleavage prior to polyadenylation. A direct repeat, 5'-AAGTGAGAGTGAT-3', is the proposed cis-regulatory element involved in 20-hydroxyecdysone repression of the UO gene. The deduced amino acid sequences of UO of D. melanogaster, rat, mouse, and pig and uricase II of soybean show 32 to 38% identity, with 22% of amino acid residues identical in all species. With use of P-element-mediated germ line transformation, 826 base pairs 5' and approximately 1,200 base pairs 3' of the D. melanogaster UO transcribed region contain all of the cis elements allowing for appropriate temporal regulation and Malpighian tubule-specific expression of the UO gene.

Molecular characterization of the Drosophila melanogaster urate oxidase gene, an ecdysone-repressible gene expressed only in the malpighian tubules

The urate oxidase (UO) gene of Drosophila melanogaster is expressed during the third-instar larval and adult stages, exclusively within a subset of cells of the Malpighian tubules. The UO gene contains a 69-base-pair intron and encodes mature mRNAs of 1,224, 1,227, and 1,244 nucleotides, depending on the site of 3' endonucleolytic cleavage prior to polyadenylation. A direct repeat, 5'-AAGTGAGAGTGAT-3', is the proposed cis-regulatory element involved in 20-hydroxyecdysone repression of the UO gene. The deduced amino acid sequences of UO of D. melanogaster, rat, mouse, and pig and uricase II of soybean show 32 to 38% identity, with 22% of amino acid residues identical in all species. With use of P-element-mediated germ line transformation, 826 base pairs 5' and approximately 1,200 base pairs 3' of the D. melanogaster UO transcribed region contain all of the cis elements allowing for appropriate temporal regulation and Malpighian tubule-specific expression of the UO gene.

Peroxisomal oxidases: cytochemical localization and biological relevance

(1) alpha-HAOX has a broad substrate specificity. In rat kidney, the enzyme reacts with aliphatic and aromatic alpha-hydroxy acids, in rat liver, however, only with aliphatic ones. (2) The best substrate for the demonstration of alpha-HAOX activity in rat and human liver is glycolate. (3) alpha-hydroxy butyric acid is the best substrate in the luminometric assay for the demonstration of alpha-HAOX activity in the rat kidney, whereas glycolate is not catalysed by the enzyme. (4) In the proximal tubulus epithelial cells of the rat kidney alpha-HAOX is concentrated in the peripheral matrix of the peroxisomes.

Postnatal development of hepatic uricase and peroxisomes in baby pigs

1. The activity of uricase, the densities of peroxisomes and cores in liver samples of baby pigs up to 4 weeks of age were investigated. 2. From 1 to 4 weeks of age, uricase activity as well as counts of cores and peroxisomes increased 5.5-, 3.3- and 2-fold. 3. Uricase activity and counts of cores and peroxisomes were correlated (P less than 0.001) with age in linear relationships. 4. Calculated for time of birth uricase activity was very low and ratio of cores to peroxisomes was 1:7. 5. From 0 to 28 days of age the calculated increases of uricase activity and counts of cores and peroxisomes were 178-, 10- and 3-fold.

Partial disassembly of peroxisomes

Rat liver peroxisomes were subjected to a variety of procedures intended to partially disassemble or damage them; the effects were analyzed by recentrifugation into sucrose gradients, enzyme analyses, electron microscopy, and SDS PAGE. Freezing and thawing or mild sonication released some matrix proteins and produced apparently intact peroxisomal "ghosts" with crystalloid cores and some fuzzy fibrillar content. Vigorous sonication broke open the peroxisomes but the membranes remained associated with cores and fibrillar and amorphous matrix material. The density of both ghosts and more severely damaged peroxisomes was approximately 1.23. Pyrophosphate (pH 9) treatment solubilized the fibrillar content, yielding ghosts that were empty except for cores. Some matrix proteins such as catalase and thiolase readily leak from peroxisomes. Other proteins were identified that remain in mechanically damaged peroxisomes but are neither core nor membrane proteins because they can be released by pyrophosphate treatment. These constitute a class of poorly soluble matrix proteins that appear to correspond to the fibrillar material observed morphologically. All of the peroxisomal beta-oxidation enzymes are located in the matrix, but they vary greatly in how easily they leak out. Palmitoyl coenzyme A synthetase is in the membrane, based on its co-distribution with the 22-kilodalton integral membrane polypeptide.

Improved isolation and purification of rat liver peroxisomes by combined rate zonal and equilibrium density centrifugation

Two different peroxisome preparations were isolated from male rat liver by using total homogenate (TH) as the starting material for one and the light mitochondrial (L) fraction for the other. The technique worked out is based on rate zonal (RZ) centrifugation in a sucrose gradient and subsequent isopycnic centrifugation in a Nycodenz gradient. The peroxisome fraction isolated from the L fraction consisted of 97-98% peroxisomal protein with catalase activity 49-fold enriched over TH. The peroxisome preparation isolated directly from TH represented about 55% of the total liver peroxisome population and had catalase activity 43-fold enriched compared with TH. The contribution of peroxisome protein to the liver protein was calculated to be in the range 1.82-2.02%. Peroxisomes isolated from TH were considerably more heterogeneous in size than peroxisomes isolated from the L fraction. Comparison of the polypeptide patterns of both preparations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed some quantitative differences. Several major polypeptides were found to be exclusively located in the peroxisome membrane. These polypeptides migrated in the gel with apparent molecular masses of 69, 42.5, 36, 26, 21, and 15 kDa.

Peroxisomal and mitochondrial palmitoyl coenzyme A beta-oxidation activities in rat white adipose tissue and their regulation in hypothyroidism

A peroxisomal fraction with catalase and CN- -insensitive palmitoyl CoA beta-oxidative activity different from the CN- -sensitive mitochondrial palmitoyl CoA beta-oxidative activity was purified from rat epididymal and perirenal white adipose tissue by differential and sucrose density gradient centrifugations. The degree of purification of this fraction as compared to the nuclei-free and fat-free homogenate was 10 and 34 for catalase and palmitoyl CoA beta-oxidative activity, respectively. The finding that it was devoid of urate oxidase activity suggests that white adipose tissue peroxisomes are anucleoid. The contributions of the peroxisomes and of the mitochondria to total beta-oxidative activity in white adipose tissue were 65 and 35%, respectively. Hypothyroidism induced a 2.0- and 2.4-fold decrease of mitochondrial and peroxisomal beta-oxidation specific activities, respectively. These results are discussed in terms of a possible thermogenic role for white adipose tissue peroxisomes.

Intraparticulate localization of some peroxisomal enzymes related to fatty acid beta-oxidation

Male Wistar rats were given a diet containing 0.05% (w/w) LK-903 (alpha-methyl-p-myristyroxycinnamic acid 1-monoglyceride) for 2 weeks. The activities of four hepatic peroxisomal enzymes involved in the fatty acyl-CoA beta-oxidizing system were determined. The activities of fatty acyl-CoA oxidase, crotonase, beta-hydroxybutyryl-CoA dehydrogenase and thiolase were all increased about three times by administration of LK-903. The intraparticulate localizations of the four enzymes were then investigated by treatment of the purified peroxisomes with Triton X-100, by sonication, and by sucrose-density-gradient centrifugation after Triton X-100 treatment. The results suggest that thiolase is localized in the matrix of peroxisomes, that crotonase and beta-hydroxybutyryl-CoA dehydrogenase are located in the core, and that all or at least part of fatty acyl-CoA oxidase is associated with the core, though its association is weak.

Cytochemical localization of catalase and several hydrogen peroxide-producing oxidases in the nucleoids and matrix of rat liver peroxisomes

The distribution of catalase, amino acid oxidase, alpha-hydroxy acid oxidase, urate oxidase and alcohol oxidase was studied cytochemically in rat hepatocytes. The presence of catalase was demonstrated with the conventional diaminobenzidine technique. Oxidase activities were visualized with methods based on the enzymatic or chemical trapping of the hydrogen peroxide produced by these enzymes during aerobic incubations. All enzymes investigated were found to be present in peroxisomes. Catalase activity was found in the peroxisomal matrix, but also associated with the nucleoid. After staining for oxidase activities the stain deposits occurred invariably in the peroxisomal matrix as well as in the nucleoids. In all experiments the activity of both catalase and the oxidases was confined to the peroxisomes. The presence of a hydrogen peroxide-producing alcohol oxidase was demonstrated for the first time in peroxisomes in liver cells. The results imply that the enzyme activity of the nucleoids of rat liver peroxisomes is not exclusively due to urate oxidase. The nucleoids obviously contain a variety of other enzymes that may be more or less loosely associated with the insoluble components of these structures.

Determination of the cross-points of rat liver peroxisomes, peroxisomal core and the core components by cross-partition

The cross-points of rat liver peroxisomes, peroxisomal core and the core components were determined by means of cross-partition in two phase systems. The partitions were carried out in the systems containing 6% (w/w) Dextran T 500 and 6% (w/w) polyethyleneglycol 4000 in sodium salts. The same cross-point, pH 5.6, was obtained in peroxisomal marker enzymes in light mitochondrial fraction of liver homogenate, such as catalase, D-amino acid oxidase and urate oxidase. The cross-point as determined by cross-partition of purified peroxisomal core was 6.7. The cross-points of urate oxidase and framework protein fractions obtained by alkali treatment on the purified core were 7.8 and 4.2, respectively, and the ratio of the proteins of urate oxidase to framework protein was 2 : 1. The theoretical value of cross-point of the core calculated from from the relationship between the cross-point and protein ratio of each component of the core coincided with the experimental value obtained by this method.

Degradation of peroxisomal catalase and urate oxidase of rat liver

Urate oxidase and catalase were purified from rat liver peroxisomes, and respective antibodies were prepared from rabbits by the administration of these enzymes. Although urate oxidase generally precipitates in immunoprecipitation-possible pH ranges (pH 4.5--9.5), the enzyme remained soluble in 50 mM glycine buffer (pH 9.5) containing 50% glycerol up to concentration of 0.3 mg/ml. Anti-urate oxidase reacted with purified urate oxidase as well as with the crude preparation. After [3H]leucine was injected to rats, urate oxidase and catalase were purified from rat liver at certain intervals, and further precipitated by respective antibodies. The half-life of the catalase was 39 h and that of urate oxidase, 20 h. When the sonicated light mitochondrial fraction was incubated at 37 degrees C and at pH 7.0 or 5.6, inactivation of catalase did not seem to differ between these pH values, and approximately 80% of the catalase activity remained even after 8 h. Urate oxidase was inactivated very rapidly at pH 5.6; only 30% of its activity survived incubation for 6 h. This inactivation was found to occur by some proteolytic process. From these findings, the turnover rate of urate oxidase was found to be different from that of catalase, and this distinction seemed to be due to different sensitivity to some degradative enzymes.

An electron microscopic and enzymic study of rat liver peroxisomal nucleoid core and its association with urate oxidase

The appearance of the characteristic crystalloid core of rat liver peroxisomes is emulated by the electron microscopic (EM) appearance of highly purified urate oxidase prepared from the same tissue. The purity of the enzyme preparation was established by gel electrophoresis under various conditions and the specific enzyme activity was at least as high as any previously reported. The amino acid composition of urate oxidase was determined. As additional evidence for close association of the peroxisomal core with urate oxidase, it was demonstrated that the biphasic changes in rat liver urate oxidase activity in response to prolonged starvation were paralleled by changes in the EM appearance of peroxisomes. Under comparable conditions catalase, another peroxisomal enzyme, did not show the same changes in activity as did urate oxidase. Evidence for the possible identity of urate oxidase with the peroxisomal crystalloid of rat liver has been presented, all materials having been obtained from, and experiments performed with, the rat.