An immobilized enzyme reactor for the detoxification of bilirubin

An immobilized enzyme reactor has been developed for the degradation of bilirubin as a potential treatment for neonatal jaundice. It utilizes the enzyme bilirubin oxidase from Myrothecium verrucaria, which in the presence of molecular oxygen converts bilirubin to biliverdin and other products that are much less toxic than bilirubin. Bilirubin oxidase was covalently attached to agarose beads using cyano transfer activation. Forty percent of the specific activity of bilirubin oxidase was retained after immmobilization, and preparations with 20 units of enzymatic activity per gram of drained wet weight of gel were obtained. The stability of bilirubin oxidase at pH 7.4 and 37 degrees C was improved fivefold by immobilization. A 15-mL column containing immobilized bilirubin oxidase, through which a 37 degrees C solution of 332muM bilirubin and 450muM human serum albumin in 0.05M phosphate buffer (pH 7.4) was passed at 1 mL/min, converted more than 60 percent of the bilirubin per pass. The substrate specificity of the enzyme and the small volume of the reactor are important characteristics for this clinical application where it is desirable to remove only one compound from the blood and to minimize the volume of blood in the extracorporeal circuit. This reactor, by detoxifying the jaundiced infant's blood of bilirubin, would eliminate the risks associated with the use of donor blood as is done currently in treating severe neonatal jaundice.     

Enzymic oxidation of unconjugated bilirubin by rat liver.

The presence of the enzyme bilirubin oxidase, which degrades bilirubin in vitro, was demonstrated in the liver. Subcellular-fractionation experiments indicate that bilirubin oxidase is located in both the inner and outer membranes of the mitochondria. The mean rate of the reaction is 1.57 +/- 0.38 (S.D.) nmol of bilirubin degraded/min per mg of mitochondrial protein (munits/mg of protein). With respect to the overall breakdown of bilirubin, the enzyme has a Km' of 136 microM-bilirubin and a Vmax.' of 9.13 munits/mg of protein. Its activity is influenced by the ionic strength of the media and is inhibited by KCN, thiol reagents, NADH and albumin. The enzyme is aerobic, and between 1 and 1.5 mol of O2 are consumed per mol of bilirubin degraded. The products of the reaction include propentdyopents. The hepatic bilirubin oxidase activity of the jaundiced Gunn-rat liver is not significantly different from that of the Sprague-Dawley rat, and it is not induced by beta-naphthoflavone.     

疣孢漆斑菌(Myrothecium Verrucaria)J-1胆红素氧化酶的纯化及性质初步研究

从中国土样中筛选到一株能产生胆红素氧化酶的微生物(Myrothecium Verrucaria)J-1,培养后,分离纯化,最后经QAE—Sephadex A50柱层析,得到胆红素氧化酶比活为207.65 U/A 280nm,总产率为22.3％。纯酶紫外吸收峰为278 nm,凝胶电泳为单一色带。分子量估计为52000。它能迅速、特异地氧化胆红素为胆绿素,并进一步氧化成目前还不清楚的紫色化合物。最佳作用pH为7.0,最佳作用温度为40℃。     

A new bilirubin-degrading enzyme from orange peels

A novel enzyme activity that catalyzes the degradation of unconjugated bilirubin (Bu) has been demonstrated in extracts of the peels of edible oranges. Unlike the few known bilirubin-oxidizing enzymes, the orange enzyme does not produce biliverdin as a product, does not seem to require oxygen, and has a unique absorption spectrum of its products. Even at the crude stage, the enzyme has a specific activity that is 10 and 20 times higher, respectively, than those reported for the crude or partially purified Bu-degrading enzymes from mushrooms and rat liver. The enzyme has a pH optimum near 7.5 and a Km value of 50-100 microM for Bu. The enzyme is remarkably stable, retaining over 50% activity after prolonged digestion with proteinase K or heating at 100 degrees C. Similar treatments inactivated the bilirubin oxidase from Myrothecium verrucaria MT-1. The enzyme is poorly soluble in water but can be partially solubilized with cholic acid, with a doubling in specific activity.     

Purification and characteristics of an enzyme with both bilirubin oxidase and laccase activities from mycelium of the basidiomycete <Emphasis Type="Italic">Pleurotus ostreatus</Emphasis>

A homogenous enzyme with both bilirubin oxidase and laccase activities was isolated from a submerged culture of the basidiomycete Pleurotus ostreatus mycelium and characterized. The yield of the enzyme was 127 μg/g dry biomass of the mycelium. The specific activity of the enzyme was 21 and 261 U/mg to bilirubin and to a laccase substrate ABTS, respectively. The intracellular phenol oxidase from the P. ostreatus mycelium was identified as bilirubin oxidase with the amino acid sequence highly homologous to that of the pox2 gene-encoded product. The enzyme displayed the maximal laccase activity at 50–55°C to all substrates examined, whereas the pH optimum was substrate-dependent and changed from 3.0 for ABTS to 7.0 for syringaldazine and guaiacol. The enzyme maintained catalytic activity within a broad pH range but was inactivated at pH 4.0. The enzyme was thermostable but very sensitive to metal chelating inhibitors. Trypan Blue (5 mg/liter) was completely decolorizated upon 3 h of incubation with the bilirubin oxidase (20 mU/ml) at room temperature.     

Myrothecium verrucaria bilirubin oxidase and its mutants for potential copper ligands

Bilirubin oxidase (EC:1.3.3.5) purified from a culture medium of Myrothecium verrucaria MT-1 (authentic enzyme) catalyzes the oxidation of bilirubin to biliverdin in vitro and recombinant enzyme (wild type) was obtained by using an overexpression system of the bilirubin oxidase gene with Aspergillus oryzae harboring an expression vector. The absorption and ESR spectra showed that both bilirubin oxidases are multicopper oxidases containing type 1, type 2, and type 3 coppers similar to laccase, ascorbate oxidase, and ceruloplasmin. Site-directed mutagenesis has been performed for the possible ligands of each type of copper. In some mutants, Cys457 --> Val, Ala, His94 --> Val, and His134.136 --> Val, type 1 and type 2 copper centers were perturbed completely and the enzyme activity was completely lost. Differing from the holoenzyme, these mutants showed type 3 copper signals. However, the optical and magnetic properties characteristic of type 1 copper were retained even by mutating one of the type 1 copper ligands, i.e., a mutant, Met467 --> Gly, showed a weak but apparent enzyme activity. A double mutant His456.458 --> Val had only type 1 Cu, showing a blue band at 600 nm (epsilon = 1.6 x 10(3)) and an ESR signal with very narrow hyperfine splitting (A parallel = 7.2 x 10(-)3 cm-1). Since the type 2 and type 3 coppers are not present, the mutant did not show enzyme activity. These results strongly imply that the peculiar sequence in bilirubin oxidase, His456-Cys457-His458, forms an intramolecular electron-transfer pathway between the type 1 copper site and the trinuclear center composed of the type 2 and type 3 copper sites.     

耐高温重组CotA蛋白的胆红素氧化酶反应动力学及活性鉴定

已知源于枯草芽孢杆菌内生孢子的CotA蛋白具有漆酶和胆红素氧化酶活性。然而,其分离纯化极为困难。本研究对表达与纯化的重组CotA蛋白的胆红素氧化酶特性及氧化还原功能进行鉴定。基因转染及筛选获得了表达CotA的P. pastoris菌株|继而,表达的重组CotA蛋白经DEAE-Sepharose FF 及Sephadex G-75层析分离与纯化,产物得率为25%,纯化产物的酶比活性为 4 U/mg。经SDS-PAGE 和 MALDI-TOF MS 分析显示,其分子质量为65 kD。纯化的CotA蛋白能够催化胆红素氧化,生成胆绿素,且催化反应速率受反应溶液中溶解氧含量的影响,提示纯化的重组CotA具有胆红素氧化酶活性。酶反应进一步证明,CotA的胆红素氧化酶反应最适pH值为pH 8.0,最适温度为60℃。该酶在90℃条件下的半衰期为7 h,提示CotA胆红素氧化酶具有高度的热稳定性。CotA修饰的摄谱仪石墨电极可直接电催化分子氧（O2）还原,具有很好的电流响应。我们的结果表明,重组的CotA蛋白具有耐高温胆红素氧化酶活性。更重要的是,我们的结果还提示重组的CotA蛋白在酶生物燃料电池阴极的制备上具有较好的应用潜能。     

Mouse protoporphyrinogen oxidase. Kinetic parameters and demonstration of inhibition by bilirubin.

The penultimate step of haem biosynthesis, the oxidation of protoporphyrinogen to protoporphyrin, was examined with purified murine hepatic protoporphyrinogen oxidase (EC 1.3.3.4) in detergent solution. The kinetic parameters for the two-substrate (protoporphyrinogen and oxygen) reaction were determined. The limiting Km for protoporphyrinogen when oxygen is saturating is 6.6 microM, whereas the Km for oxygen with saturating concentrations of protoporphyrinogen is 125 microM. The kcat. for the overall reaction is 447 h-1. The ratio of kcat. to the Km for protoporphyrinogen is approx. 20-fold greater than the kcat./Km,O2 ratio. The ratio of protoporphyrin formed to dioxygen consumed is 1:3. Ubiquinone-6, ubiquinone-10 and dicoumarol stimulate protoporphyrinogen oxidase activity at low concentrations (less than 15 microM), whereas coenzyme Q0 and menadione show no activation at these concentrations. Above 30 microM, all five quinones inhibit the enzyme activity. FAD does not significantly affect the activity of the enzyme. Bilirubin, a product of haem catabolism, is shown to be a competitive inhibitor of the penultimate enzyme of the haem-biosynthetic pathway, protoporphyrinogen oxidase, with a calculated Ki of 25 microM. The terminal enzyme of haem-biosynthetic pathway, namely ferrochelatase, is not inhibited by bilirubin at concentrations over double the Ki value for the oxidase. In contrast with other enzymic systems, the toxicity of bilirubin is not reversed by binding to albumin.     

Bilirubin oxidase from Bacillus pumilus: a promising enzyme for the elaboration of efficient cathodes in biofuel cells

A CotA multicopper oxidase (MCO) from Bacillus pumilus, previously identified as a laccase, has been studied and characterized as a new bacterial bilirubin oxidase (BOD). The 59 kDa protein containing four coppers, was successfully over-expressed in Escherichia coli and purified to homogeneity in one step. This 509 amino-acid enzyme, having 67% and 26% sequence identity with CotA from Bacillus subtilis and BOD from Myrothecium verrucaria, respectively, shows higher turnover activity towards bilirubin compared to other bacterial MCOs. The current density for O(2) reduction, when immobilized in a redox hydrogel, is only 12% smaller than the current obtained with Trachyderma tsunodae BOD. Under continuous electrocatalysis, an electrode modified with the new BOD is more stable, and has a higher tolerance towards NaCl, than a T. tsunodae BOD modified electrode. This makes BOD from B. pumilus an attractive new candidate for application in biofuel cells (BFCs) and biosensors.     

Purification, characterization and decolorization of bilirubin oxidase from Myrothecium verrucaria 3.2190

Myrothecium verrucaria 3.2190 is a nonligninolytic fungus that produces bilirubin oxidase. Both M. verrucaria and the extracellular bilirubin oxidase were tested for their ability to decolorize indigo carmine. The biosorption and biodegradation of the dye were detected during the process of decolorization; more than 98% decolorization efficiency was achieved after 7 days at 26°C. Additionally, the crude bilirubin oxidase can efficiently decolorize indigo carmine at 30°C~50°C, pH 5.5~9.5 with dye concentrations of 50 mg l(-1)~200 mg l(-1). Bilirubin oxidase was purified and visualized as a single band on native polyacrylamide gel electrophoresis (PAGE). Several enzymatic properties of the purified enzyme were investigated. Moreover, the identity of the purified bilirubin oxidase (BOD) was confirmed by matrix assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS). These results demonstrate that the purified bilirubin oxidase in M. verrucaria strain has potential application in dye effluent decolorization.     

An in vitro model of aneurysmal subarachnoid hemorrhage: oxidation of unconjugated bilirubin by cytochrome oxidase

Aneurysmal subarachnoid hemorrhage is a stroke subtype with high rates of mortality and morbidity. Cerebral vasospasm can lead to ischemic injury or death and is a common complication of aneurysmal subarachnoid hemorrhage, usually occurring 3-9 days afterwards. The cause of vasospasm is not known. Recently, there has been strong evidence that vasoactive oxidation products of bilirubin may be involved. Currently, the factors that lead to bilirubin oxidation are poorly characterized. In this study, we have designed an in vitro model of hemorrhagic stroke in order to investigate conditions that promote the oxidation of bilirubin to form vasoactive compounds. Using our model, we created a basic hematoma system of blood, CSF, and hemeoxygenase-1. We manipulated this system in various ways, incubated it and determined the concentration of vasoactive bilirubin oxidation products that resulted. Conditions where cytochrome oxidase was stimulated caused an increase bilirubin oxidation products (292.6 +/- 39.9 micromol/L respectively, vs. 79.3 +/- 1.3 micromol/L for the basic reaction, p < 0.05), which was attenuated by cyanide. Our data suggest that bilirubin oxidation products may be produced by oxidation(s) requiring an oxygen-utilizing enzyme like cytochrome oxidase.     

NADH dehydrogenase of Corynebacterium glutamicum. Purification of an NADH dehydrogenase II homolog able to oxidize NADPH

NADPH oxidase activity, in addition to NADH oxidase activity, has been shown to be present in the respiratory chain of Corynebacterium glutamicum. In this study, we tried to purify NADPH oxidase and NADH dehydrogenase activities from the membranes of C. glutamicum. Both the enzyme activities were simultaneously purified in the same fraction, and the purified enzyme was shown to be a single polypeptide of 55 kDa. The N-terminal sequence of the enzyme was consistent with the sequence deduced from the NADH dehydrogenase gene of C. glutamicum, which has been sequenced and shown to be a homolog of NADH dehydrogenase II. In addition to high NADH-ubiquinone-1 oxidoreductase activity at neutral pH, the purified enzyme showed relatively high NADPH oxidase and NADPH-ubiquinone-1 oxidoreductase activities at acidic pH. Thus, NADH dehydrogenase of C. glutamicum was shown to be rather unique in having a relatively high reactivity toward NADPH.     

Bilirubin oxidase activity of Bacillus subtilis CotA

The spore coat protein CotA from Bacillus subtilis was previously identified as a laccase. We have now found that CotA also shows strong bilirubin oxidase activity and markedly higher affinity for bilirubin than conventional bilirubin oxidase. This is the first characterization of bilirubin oxidase activity in a bacterial protein.     

Bilirubin Oxidase Activity of Bacillus subtilis CotA

The spore coat protein CotA from Bacillus subtilis was previously identified as a laccase. We have now found that CotA also shows strong bilirubin oxidase activity and markedly higher affinity for bilirubin than conventional bilirubin oxidase. This is the first characterization of bilirubin oxidase activity in a bacterial protein.     

The water-dependence of the catalytic activity of bilirubin oxidase suspensions in low-water systems.

We investigated the enzymic activity of bilirubin oxidase when it is suspended as a lyophilized powder in a low-water system. The enzyme required buffer salts and a source of water to show activity. This study investigated the complete range of water thermodynamic activity (a(w)) by combining the use of salt hydrates and two-phase systems with concentrated solutes in the aqueous phase. When free water was added, activity reached a maximum at a defined water content, but this maximum increased with buffer content, suggesting that there was competition for water with the buffer salts from which the enzyme was lyophilized. Alternatively, a range of salt hydrates was used, each able to fix the water activity (a(w)) at a different value. By providing water to the organic solvent phase in this way, the dependency of enzyme activity upon a(w) was investigated and shown to be independent of buffer concentration. However, the optimum a(w) was uncertain because the available a(w) range for salt hydrates is < or = 0.90. Investigation of the remaining water activity range was made possible by using an a(w) depressor (sorbitol) to lower the a(w) of a two-phase system. The optimum a(w) for the bilirubin oxidase activity in this two-phase system was a(w) = 0.936, independent of buffer concentration. The study therefore confirmed the need to control the water 'available' to low-water systems and the dependence of enzyme activity on water thermodynamic activity (a(w)) not water content.     

Enzymatic removal of bilirubin toxicity by bilirubin oxidase in vitro and excretion of degradation products in vivo

The toxic effects of the degradation products of bilirubin that were formed by reaction with bilirubin oxidase were investigated with the C 1300 mouse neuroblastoma cell line by examining the following parameters: growth inhibition, morphologic characteristics, membrane transport, DNA synthesis, and protein synthesis. The addition of bilirubin to the cells resulted in definite cytotoxic effects on all of these parameters in a dose-dependent fashion; the addition of bilirubin oxidase reversed the toxic effects on the C 1300 cells in vitro. Furthermore, we found that most of these enzymatic degradation products of bilirubin were excreted by the kidney into the urine in a few hours after intravenous injection of the degradation products; in contrast, no intact bilirubin was excreted. Thus, these findings suggest that hyperbilirubinemia in newborn infants (kernicterus) may be prevented by administering polyethylene glycol-conjugated bilirubin oxidase, with a longer plasma half-life which has been reported previously to oxidize bilirubin to its nontoxic components in the bloodstream.     

Cytokinin oxidase: Biochemical features and physiological significance

The catabolism of cytokinin in plant tissues appears to be due, in large part, to the activity of a specific enzyme, cytokinin oxidase. This enzyme catalyses the oxidation of cytokinin substrates bearing unsaturated isoprenoid side chains, using molecular oxygen as the oxidant. In general, substrate specificity is highly conserved and cytokinin substrates bearing saturated or cyclic side chains do not serve as substrates for most cytokinin oxidases tested to date. Despite variation in molecular properties of the enzyme from a number of higher plants, oxygen is always required for the reaction. Cytokinin oxidases from several sources have been shown to be glycosylated. Cytokinin oxidase activity appears to be universally inhibited by cytokinin-active urea derivatives. Auxin has been reported to act as an allosteric regulator which increases activity of the enzyme.
Cytokinin oxidase activity is subject to tight regulation. Levels of the enzyme are controlled by a mechanism sensitive to cytokinin supply. The up-regulation of cytokinin oxidase expression in response to exogenous application of cytokinin suggests that the metabolic fate of exogenously applied cytokinins may not accurately mimic that of the endogenous compounds.
Cytokinin oxidase is believed to be a copper-containing amine oxidase (EC 1.4.3.6). Considerable evidence strongly supports a common mechanism for amine oxidases. It is possible that advances in understanding of other amine oxidases could be extrapolated to increase our understanding of cytokinin oxidase at the molecular level. This is discussed with reference to what is currently known about the catalytic mechanism of the enzyme. The possibility of pyrroloquinoline quinone, or a closely related compound, as a redox cofactor of cytokinin oxidase is considered, as are the implications of the glycosylated nature of the enzyme for its regulation and compartmentalisation within the cell.     

Factor affecting enzyme characteristics of bilirubin oxidase suspensions in organic solvents

The activity of bilirubin oxidase toward bilirubin was studied in a liquid/solid two-phase low-water organic system using a simple spectrophotometric assay to follow the reaction. The enzyme was lyophilized from aqueous solution before being suspended in the organic solvent reaction medium. The activity was significantly influenced by the properties of the aqueous medium from which the enzyme was lyophilized, specifically its pH, and the quantity and nature of the buffering species. Analyses of these effect showed that the role of buffering species in such systems went beyond their effect in fixing the protonation state of the enzyme. The activity was also influenced by the quantity of water added to the organic solvent reaction medium. The reaction was shown to follow Michaelis-Menten Kinetics, and K(m) and k(cat) were determined. The liquid/solid two-phase system studied was extensively compared to a previously studied water-in-oil microemulsion system (c) 1993 Wiley & Sons, Inc.     

Authentic and recombinant bilirubin oxidases are in different resting forms

Myrothecium verrucaria bilirubin oxidase expressed in Aspergillus oryzae is in a resting form different from that of the authentic bilirubin oxidase, but reaches the resting form of the authentic enzyme after one cycle of reduction and reoxidation with dioxygen as shown by the absorption and electron paramagnetic resonance spectra.     

Photoinduced Decarboxylation-dependent Transamination of Pyridoxal 5′-Phosphate-α-Amino Acid Schiff Bases

Bilirubin oxidase was purified from the culture filtrate of Myrothecium verrucaria MT-1 by a procedure involving ammonium sulfate precipitation, charcoal treatment, and QAE-Sephadex A-50 and Sephadex G-100 column chromatographies. The purified enzyme was homogeneous on disc gel electrophoresis.

Copper and carbohydrate were contained in the enzyme. The enzyme was inhibited by Fe²⁺ and compounds that complex with copper. Bilirubin, biliverdin, hemin and chlorophyllin which consist of tetrapyrrole, and substrates of laccase were oxidized by the enzyme. Bilirubin was oxidized more rapidly than other substances. Bilirubin oxidase differed from laccase in reactivity with substances consisting of tetrapyrrole. Substances consisting of tetrapyrrole were oxidized only a little by laccase but rapidly oxidized by bilirubin oxidase. The apparent Km value for bilirubin was calculated to be 190 μm.