Urate Oxidase Activity Research Articles

Characterization of glyoxysomes in yeasts and their transformation into peroxisomes in response to changes in environmental conditions

During growth of the yeasts Candida utilis and Hansenula polymorpha in mineral media containing ethanol as a carbon source and ammonium sulphate as a nitrogen source, the specific activities of isocitrate lyase and malate synthase were significantly increased when compared to glucose/ammonium sulphate-grown cells. In addition to the enhanced levels of these glyoxylate cycle enzymes, an increase in the specific activities of d-amino acid oxidase, amine oxidase or urate oxidase was observed when ammonium sulphate in the ethanol medium was replaced by d-alanine, methyl- or ethylamine, or uric acid. The subcellular localization of these enzymes was investigated by cell fractionation studies involving homogenization of protoplasts followed by differential and sucrose gradient centrifugation. In ethanol/ammonium sulphate-grown cells, isocitrate lyase and malate synthase cosedimented in a fraction together with catalase and part of the malate dehydrogenase. Electron microscopy revealed that this fraction consisted of microbodies which must be regarded as glyoxysomes. Two other glyoxylate cycle enzymes, citrate synthase and aconitase together with the other part of malate dehydrogenase, cosedimented with cytochrome c oxidase, a mitochondrial marker enzyme. In ethanol/d-alanine-, ethanol/methylamine- or ethanol/ethylamine-grown C. utilis and ethanol/uric acid-grown H. polymorpha, a peroxisomal enzyme, i.e. d-amino acid oxidase, amine oxidase or uric acid oxidase cosedimented with the glyoxysomal key enzymes. Cytochemical staining experiments demonstrated that in these variously-grown cells the activities of the oxidases were confined to the microbodymatrix; this also contained malate synthase activity.

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

A peroxisomal fraction with catalase and CN −-insensitive palmitoyl CoA β-oxidative activity different from the CN −-sensitive mitochondrial palmitoyl CoA β-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 β-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 β-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 β-oxidation specific activities, respectively. These results are discussed in terms of a possible thermogenic role for white adipose tissue peroxisomes.

Hepatic enzymes, coash and long-chain acyl-coa in subcellular fractions as affected by drugs inducing peroxisomes and smooth endoplasmic reticulum

1. 1. The activities of acyl-CoA hydrolase, catalase, urate oxidase and peroxisomal palmitoylCoA oxidation as well as the protein content and the level of CoASH and long-chain acyl-CoA were measured in subcellular fractions of liver from rats fed diets containing phenobarbital (0.1% w/w) or clofibrate (0.3% w/w). 2. 2. Whereas phenobarbital administration resulted in increased microsomal protein, the clofibrateinduced increase was almost entirely attributed to the mitochondrial fraction with minor contribution from the light mitochondrial fraction. 3. 3. The specific activity of palmitoyl-CoA hydrolase in the microsomal fraction was only slightly affected while the mitochondrial enzyme was increased to a marked extent (3–4-fold) by clofibrate. 4. 4. Phenobarbital administration mainly enhanced the microsomal palmitoyl-CoA hydrolase. 5. 5. The increased long-chain acyl-CoA and CoASH level observed after clofibrate treatment was mainly associated with the mitochondrial, light mitochondrial and cytosolic fractions, while the slight increase in the levels of these compounds found after phenobarbital feeding was largely of microsomal origin. 6. 6. The findings suggest that there is an intraperoxisomal CoASH and long-chain acyl-CoA pool. 7. 7. The specific activity of palmitoyl-CoA hydrolase, catalase and peroxisomal palmitoyl-CoA oxidation was increased in the lipid-rich floating layer of the cytosol-fraction. 8. 8. The changes distribution of the peroxisomal marker enzymes and microsomal palmitoyl-CoA hydrolase after treatment with hypolipidemic drugs may be related to the origin of peroxisomes.

Temporal control of urate oxidase activity during development of the third‐instar larva of Drosophila: The role of 20‐hydroxyecdysone

AbstractThe tissue‐specific enzyme urate oxidase is confined exclusively to the Malpighian tubules of Drosophila melanogaster and expressed only in the third‐instar larva and the adult. Shortly before pupariation urate oxidase activity declines precipitously and is not detectable 24 hours later. That 20‐hydroxyecdysone is the factor that triggers the disappearance of urate oxidase activity in late third‐instar larvae is demonstrated using the temperature sensitive mutant ecd1 which at the nonpermissive temperature of 29°C fails to accumulate a sufficient concentration of 20‐hydroxyecdysone necessary for puparium formation and thus remains a third‐instar larva for 1 to 2 weeks before death. Both the life cycle and the temporal profile of urate oxidase activity in ecd1 larvae at 19°C is identical to that of the wild type. However, at 29°C ecd1 third‐instar larvae retain high urate oxidase activity. A precipitous decline in urate oxidase activity is observed when ecd1 larvae at 29°C are fed 20‐hydroxyecdysone. These data implicate 20‐hydroxyecdysone in the process that controls the rapid decline of urate oxidase activity at the time of puparium formation. In whole homogenates of Malpighian tubules, the urate oxidase polypeptide was identified in SDS‐polyacrylamide gels by its Rf with respect to homogeneously pure Drosophila urate oxidase and also by immunoprecipitation with rabbit anti‐Drosophila urate oxidase IgG. Throughout development the amount of the urate oxidase polypeptide is correlated with the magnitude of urate oxidase activity.

Effects of chronic modification of dietary fat and carbohydrate in rats.

1. Rats were fed on diets enriched with starch, sucrose, corn oil or beef tallow for 3 weeks and the activities of various enzymes in the liver were measured. 2. The mitochondrial glycerol phosphate acyltransferase activity was lower in rats fed on the starch diet than on the two high-fat diets. 3. The non-microsomal (presumably peroxisomal) dihydroxyacetone phosphate acyltransferase activity was higher in rats fed on the starch diet and corn-oil diets than in those fed on the sucrose and beef-tallow diets. Urate oxidase activity was higher in rats fed on the starch diet than in the three other groups. There were no significant differences in the activity of acyl-CoA oxidase among the groups. 4. The activity of soluble phosphatidate phosphohydrolase was not significantly different among the dietary groups. There were increases of 3.3--4.3-fold in this activity in the dietary groups 6h after injection of corticotropin. The equivalent increases for the mitochondrial glycerol phosphate acyltransferase were 1.4--1.6 fold. 5. The corticosterone responses to the corticotropin injection were not significantly different between dietary groups. However, the corticosterone response of the rats fed on the two high-fat diets was prolonged when the rats were given an acute load of fructose [Brindley, Cooling, Glenny, Burditt & McKechnie (1981) Biochem. J. 200. 275--283]. 6. Rats fed on the high-fat diets had higher concentrations of circulating cholesterol than those fed on the starch and sucrose diets. Serum triacylglycerol concentrations were lower in the rats fed on the starch diet than in the three other groups. 7. The results are discussed in terms of the relationship between diet, hormonal balance and hepatic glycerolipid metabolism.

Induction of peroxisomal enzymes in rat liver by the hypolipidemic agent LK-903

The effect of the hypolipidemic agent LK-903 on enzyme activities in hepatic peroxisomes of the rat was investigated. After administration of LK-903 with the chow for 14 days, the activities of hepatic catalase, urate oxidase, d-amino acid oxidase, and the fatty acyl-CoA oxidizing system were increased 2-fold, 2-fold, 2.5-fold and 7-fold, respectively. Subcellular fractionation showed that these peroxisomal enzyme activities were concentrated in the heavy mitochondrial fraction. In contrast, the peroxisomal enzyme activities of control rats were highest in the light mitochondrial fraction. During administration of LK-903, the activities of the particulate catalase, urate oxidase, and fatty acyl-CoA oxidizing system increased gradually, and reached plateau levels in about 12 days. When the rats that had received LK-903 for 14 days were subsequently given the basal diet, the particulate urate oxidase activity decreased gradually, but the activities of catalase and the fatty acyl-CoA oxidizing system remained almost unchanged for 7 days. The enhancement of catalase activity by LK-903 was due to an increase in the synthesis rate of over 2-fold; the half-life and the degradation-rate were unchanged.

Effects of some hypolipidemic drugs on biochemical values and on hepatic peroxisomal enzymes of normolipemic rat.

Effects of vitamin B2-butyrate, nicomol, ML-236B, KF 1492 and pantethine, which are hypolipidemic drugs, on biochemical values and on hepatic peroxisomal enzymes of normolipemic rat. 1) Vitamin B2-butyrate (100 mg/kg) and nicomol (lg/Kg) increased carnitine acetyltransferase and D-amino acid oxidase activities, respectively, while these drugs had no influence on body weight, liver weight, serum and liver triglyceride, and serum and liver cholesterol levels. 2) ML-236B (300 mg/kg) had no influence on biochemical values and on activities of peroxisomal enzymes containing catalase. 3) KF 1492 (300 mg/kg) had no influence on the biochemical values, but an increase in the activities of fatty acyl-CoA oxidizing system (FAOS) and carnitine acetyltransferase (CAT) participating hepatic lipid metabolism was observed. 4) Pantethine (lg/kg) had no influence on the biochemical values, except a little decrease in the growth rate. However, increase by about 10% in the activities of urate oxidase and D-amino acid oxidase was observed. Catalase activity was decreased to 60% of control level. From these results, it is concluded that, in contrast to clofibrate, vitamin B2-butyrate, nicomol, ML-236B, KF 1492 and pantethine have little influence on the lipid metabolism of normolipemic animal and on the hepatic peroxisomal enzymes, indicating that the action mechanism of these drugs may be different from that of clofibrate and that the participation of hepatic peroxisomes in hypolipidemic activities of these drugs may be little if any.

Control by phytochrome of urate oxidase and allantoinase activities during peroxisome development in the cotyledons of mustard (Sinapis alba L.) seedlings

The peroxisomal enzyme, urate oxidase (EC 1.7.3.3), and the next enzyme of the urate pathway, allantoinase (EC 3.5.2.5), demonstrate a lightmediated rise of activity in the cotyledons of mustard (Sinapis alba L.). The capacity of the peroxisomes for urate breakdown, marked by the time course of urate oxidase, develops distinctly later than the two other peroxisome functions (fatty acid breakdown, "glyoxysomal" function; glycolate breakdown, "leaf peroxisomal" function). The light effect on urate oxidase and allantoinase is mediated through the phytochrome system in all three seedling organs (cotyledons, hypocotyl, radicle), as revealed by induction/reversion experiments with red/far-red light pulses and continuous irradiation with far-red light (high irradiance reaction of phytochrome). Both enzyme activities can be induced by phytochrome in the seedling cotyledons only during a sensitive period of about 48 h prior to the actual light-mediated rise of activity, making it necessary to assume the existence of a long-lived intermediate ("transmitter") in the signal response chain connecting enzyme formation to the phytochrome system. Detailed kinetic investigation, designed to test whether urate oxidase and allantoinase are controlled by phytochrome via the same signal response chain (coordinate induction), revealed large differences between the two enzymes: (i) a different onset of the loss of reversibility of a red light induction by a far-red light pulse (=onset of transmitter formation=coupling point; 48 h/24 h after sowing for urate oxidase/allantoinase); (ii) a different onset of the response (=onset of competence for transmitter= starting point; 72 h/48 h); (iii) full loss of reversibility (=completion of transmitter formation) is reached at different times (independence point, 90 h/52 h). These differences show that phytochrome controls urate oxidase and allantoinase via separate signal response chains. While urate oxidase can be localized in the peroxisomal fraction isolated from crude organelle extracts of the cotyledons by density gradient centrifugation, most of the allantoinase activity found in the peroxisomal fraction did not appear to be an integral part of the peroxisome but originated presumably from adhering membrane fragments.

Heterogeneity of microbodies in a blowfly, Aldrichina grahami

1. 1. Microbodies are present in Malpighian tubules, fat body and gut in a blowfly, A. grahami. 2. 2. Those in Malpighian tubules are nucleoid type and contain urate oxidase and catalase. D-Amino acid oxidase and catalase are contained in the particles of fat body and gut. 3. 3. The nucleoids in microbodies of Malpighian tubules seem to be loosened when the urate oxidase activity disappears during the metamorphosis.

Effects of clofibrate administration to rats on their hepatocytes

Changes in the hepatocytes of rats treated with the hypolipidemic agent clofibrate for a 1 week period were investigated. During this time liver weight increased while, in contrast to peroxisomes, mitochondrial and microsomal protein were not changed significantly. While there was no effect on cytochrome oxidase activity carnitineacetyl transferase activity increased more than 20-fold. The urate oxidase activity of the homogenate decreased about 30% and palmitoyl-CoA oxidation increased more than 10 times. The ratio of protein to phospholipid in microsomes was not affected, nor were the rates of incorporation of [ 3H]leucine, [ 3H]glycerol and [ 3H]mevalonate into total protein, phospholipid and cholesterol, respectively. Injection of labeled glucosamine, mannose and galactose into the animals revealed an increased incorporation of these substances into lipid intermediates and endogenous luminal and membranous protein acceptors after clofibrate treatment. The significant stimulation of enzymes participating in hydroxylation reactions may be the main reason for the complex cellular changes brought about by clofibrate.

An electron microscopical study of the development of peroxisomes during formation and germination of ascospores in the methylotrophic yeast Hansenula polymorpha.

Ascospore formation was studied in liquid cultures of the yeast Hansenula polymorpha, previously grown under conditions in which the synthesis of alcohol oxidase was repressed (glucose as growth substrate) or derepressed (methanol, glycerol and dihydroxyacetone as growth substrates and after growth on malt agar plates). In ascospores obtained from repressed cells, generally one small peroxisome was present. The organelle probably originated from the small peroxisome, originally present in the vegetative cells. They had no crystalline inclusions and cytochemical experiments indicated the presence of catalase, urate oxidase and amino acid oxidase activities in these organelles. In ascospores obtained from derepressed cells, generally 1--3 crystalline peroxisomes were observed. These organelles also originated from the peroxisomes originally present in the vegetative cells by means of fragmentation or division. They contained, in addition to the enzymes characteristic for peroxisomes in spores from repressed cells, also alcohol oxidase. The latter enzyme is probably responsible for the crystalline substructure of these peroxisomes. Peroxisomes had no apparent physiological function in the process of ascosporogenesis. A glyoxysomal function of the organelles during germination of the ascospores was also not observed. Germination of mature ascospores in media containing different sources of carbon and nitrogen showed that the function of the peroxisomes present in ascospores of Hansenula polymorpha is probably identical to that in vegetative haploid cells. They are involved in the oxidative metabolism of different carbon and nitrogen sources. Their enzyme profile is a reflection of that peroxisomes of vegetative cells and their presence may enable the formation of cells which are optimally adapted to environmental conditions extant during spore germination.

Clofibrate-like effects of acetylsalicylic acid on peroxisomes and on hepatic and serum triglyceride levels

The effects of acetylsalicylic acid on (1) triglyceride levels of rat liver and rat serum, (2) peroxisomal enzyme activities, and (3) peroxisome-associated polypeptide content were investigated. The rats were maintained on diets containing 1% acetylsalicylic acid for 2 weeks. The triglyceride levels of the livers and sera of rats fed acetylsalicylic acid decreased by 23 and 65 per cent respectively. Cyanide-insensitive palmitoyl-CoA oxidizing activity in the livers of treated rats was 3.7 times greater than in controls, but the activities of catalase and urate oxidase were increased slightly. The observed increase in the hepatic palmitoyl-CoA oxidizing activity was presumably due to an enhancement of the activity in peroxisomes. Furthermore, an increase in the content of a polypeptide associated with peroxisomes in the light mitochondrial fractions from the livers of treated rats was revealed by SDS-polyacrylamide gel electrophoresis. The observed effects of acetylsalicylic acid were very similar to those of clofibrate, a hypolipidemic drug, pointing to a possibility that these effects may be common phenomena in drug-induced proliferation of peroxisomes.

The stimulation of erucate metabolism in isolated rat hepatocytes by rapeseed oil and hydrogenated marine oil-containing diets

1. 1. The metabolism of palmitate and especially of erucate was studied in hepatocytes isolated from rats fed for 3 weeks a diet containing peanut oil (diet, 1), rapeseed oil (diet 2) and partially hydrogenated marine oil (diet 3). 2. 2. The metabolism of palmitate was not significantly influenced by the diet. The rapeseed oil diet caused 1.4 fold and 1.3 fold increase and marine oil diet 3 fold and 2.2 fold increase in the oxidation and chain-shortening respectively of [14- 14C]erucic acid in isolated hepatocytes. 3. 3. Cyanide and antimycin A did not inhibit the chain-shortening of erucate in liver cells of rats fed rapeseed oil and peanut oil. The high capacity of the chain-shortening system in hepatocytes of marine oil-fed rats was partially inhibited. 4. 4. Inhibition of the transfer of fatty acids into the mitochondria by lowering the intracellular carnitine concentration and/or by addition of (+)-decanoylcarnitine resulted in a very pronounced apparent stimulation of the chainshortening of erucic acid. It is suggested that the chain-shortening system may be virtually independent of the mitochondria, unless the availability of the extramitochondrial NAD + and/or NADP + is rate-limiting under conditions of extremely low redox potential of the mitochondria. 5. 5. Feeding marine oil or rapeseed oil to the rats induced a 30% increase in catalase activity, a 25–30% increase in urate oxidase activity and a 50% increase in the total CoA in the liver compared to rats fed peanut oil. 6. 6. It is suggested that the increased metabolism of erucate in hepatocytes of marine oil and rapeseed oil-fed rats may be due to the increase in the peroxisomal β-oxidation.

Effect of triton WR-1339 on peroxisomal enzymes of rat liver

The effect of Triton WR-1339 on peroxisomal enzymes of rat liver was studied. The dose vs. response relationships of peroxisomal enzyme activities to Triton WR-1339 were first examined 3.5 days after injection. Catalase activity was reduced to 50% of that of the control at a dose of 200 mg per 100 g body weight; it was found that the decrease depended on the dose of this compound. Urate oxidase activity was not significantly affected. D-Amino acid oxidase activity showed intermediate behavior. The activities of these enzymes were found to be reduced more markedly at 2 days than at 3.5 days after injection, and subsequently the levels of the activities recovered. At 2 days after injection of a dose of 200 mg per 100 g body weight, the activities of catalase, D-amino acid oxidase and urate oxidase had decreased to 40, 60 and 60%,respectively, of the control values. It was found that the decreases in the activities of these enzymes caused by Triton WR-1339 had occurred in the large granule fraction, but not in the cytoplasm. Measurement of the specific activity, Ouchterlony gel diffusion and quantitative immunoprecipitation suggested that there was a similarity between the Triton WR-1339-treated and untreated rats in the nature of purified catalases. These results suggest that Triton WR-1339 depresses the activities of liver peroxisomal enzymes, especially the catalase activity.

Some characteristics of peroxisomes in the slime mold, Dictyostelium discoideum.

Some characteristics of peroxisomes in the slime mold, Dictyostelium discoideum were studied biochemically. The slime mold contained only two peroxisomal enzymes, urate oxidase and catalase. Both activities were concentrated highest in the light mitochondrial fraction, while the highest activity of acid phosphatase as a marker of lysosomes was found in the heavy mitochondrial fraction. Sucrose density gradient centrifugation showed that the density of peroxisomes was 1.21--1.22 g/ml, and that of lysosomes was approximately 1.21 g/ml. When the light mitochondrial fraction was treated with deoxycholate, major activities of urate oxidase, catalase, and acid phosphatase were solubilized. With development of the slime mold, both activities of urate oxidase and catalse increased at the stationary stage (4--6 h after) to a great extent and also slightly at the aggregation stage (10--12 h), thereafter they decreased gradually. Acid phosphatase remained with moderately high activity till the culmination stage (18--20 h), and then disappeared rapidly. It was found that enhanced activities of peroxisomal enzymes at the stationary stage represented an increase in the particle fraction and supernatant. On the other hand, activities of acid phosphatase at the same stage increased two-fold only in the supernatant, while the activity in the particle fraction was reduced to one-half.

A new colorimetric determination of d-amino acid oxidase and urate oxidase activity

A new method of colorimetric determination of d-amino acid oxidase and urate oxidase using catalase and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole is reported. This method is based on the combination of two steps of enzyme reactions and colorimetric procedure. The values obtained by this method are satisfactorily correlated with those obtained by the dinitrophenylhydrazine method for d-amino acid oxidase activity and the ultraviolet method for urate oxidase activity and showed good reproducibility and accuracy. It is considered that the method can be useful as a method of activity determination for studying enzyme kinetics and the reaction mechanism.

Differential increase of hepatic peroxisomal, mitochondrial and microsomal carnitine acyltransferases in clofibrate-fed rats

Hepatic peroxisomes, mitochondria and microsomes from control and clofibrate-treated animals were separated by isopycnic sucrose gradient centrifugation and the carnitine acyltransferase system studied in each of these organelles. Clofibrate treatment produced a 13-fold increase in the total activity of carnitine acetyltransferase and a 5-fold increase in carnitine octanoyl- and palmitoyl-transferase activities. The specific activities of the transferases in all three subcellular locations increased, but to different extents. Peroxisomal and microsomal carnitine acetyltransferases doubled in specific activity; the mitochondrial enzyme increased 10-fold. Peroxisomal, mitochondrial and microsomal carnitine octanoyltransferases all increased 3-fold in specific activity. Carnitine palmitoyltransferase, which is found only in mitochondria, increased 3-fold in specific activity. These differential increases changed the per cent distribution of total carnitine acetyltransferase from 50 per cent in the mitochondria of control livers to 90 per cent in treated livers. Peroxisomes from clofibrate-treated livers had a consistently greater isopycnic density in sucrose gradients. Total catalase activity increased 2-fold upon treatment and a greater percentage of it was found in the paniculate fractions. The specific activity of peroxisomal catalase and urate oxidase remained the same as in controls. Carnitine acetyl- and octanoyltransferases are the first reported enzymes whose peroxisomal specific activity increases with clofibrate treatment. Preliminary results of treatment with another membrane-inducing drug, phenobarbital, indicated no change in peroxisomal density, catalase distribution and activity, and no effect on the specific activities of the peroxisomal, mitochondrial and microsomal carnitine acyltransferases.

Temporal Control of Urate Oxidase Activity in Drosophila : Evidence of an Autonomous Timer in Malpighian Tubules

The appearance of urate oxidase activity in the Malpighian tubules of Drosophlia melanogaster is synchronized with the time of emergence of the imago from the puparium. A developmental clock within the Malpighian tubules specifies the time of appearances of urate oxidase activity.

Synthesis and total excretion of waste nitrogen by fish of the periophthalmus (mudskipper) and scartelaos families

1. 1. The terrestrial gill fish Periophthalmus expeditionium, Periophthalmus gracilis and Scartelaos histophorus excrete both ammonia and urea but no detectable uric acid. 2. 2. Urea constitutes up to 33% of combined urea and ammonia excreted. 3. 3. Liver extracts showed arginase and ornithine carbamoyltransferase activities but other enzymes of the ornithine-urea cycle were not detected. 4. 4. Urate oxidase, allantoinase and allantoicase activities were present in liver extracts of P. gracilis and P. expeditionium.

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

The peroxisomal core from the liver of rats was purified 450-fold as a marker of urate oxidase [EC 1.7.3.3.] activity. This preparation has a high specific activity of urate oxidase but not of other peroxisomal enzymes: D-amino acid oxidase [EC 1.4.3.3.], L-alpha-hydroxy acid oxidase [EC 1.1.3.15], or catalase [EC 1.11.1.6]. No activity of marker enzymes for other subcellular particles; cytochrome c oxidase [EC1.9.3.1] (mitochondria), acid phosphatase [EC 3.1.3.2] (lysosomes), or glucose-6-phosphatase [EC 3.1.3.9] (microsomes), was detected in this preparation. The core obtained showed a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the position of the band was found to correspond to a molecular weight 35,000. When the peroxisomal core was subjected to treatment at various pH's with 0.1 M carbonate buffer, urate oxidase was almost completely solubulized at pH 11.0, although approximately 35% of the core protein still remained in the pellet After solubilization of the core at pH 11.0, the specific activity of urate oxidase in the supernatant increased about 1.6 times; the density of the insoluble protein remaining in the pellet was identical with the that of the original core on sucrose density gradient centrifugation.