蔗糖酶和GOD的共固定化研究

本文研究了用吸附交联技术共固定化蔗糖酶和葡萄糖氧化酶（ＧＯＤ）的方法,考查了共固定化酶的动力学性质。试验结果表明：与溶液酶相比较,固定化蔗糖酶和ＧＯＤ的响应滞迟期分别为３分钟和２分钟,４态响应时间增加６分钟和４分钟,Ｋｍ值增大,ｐＨ─活力曲线变宽,最适ｐＨ值分别增大０．７和０．６４,最适温度则降低７．３℃和１６℃。以活性氧化铝作载体,戊二醛作交联剂制备的共固定化蔗糖酶和ＧＯＤ,其蛋白质固定化率为９２．９％,分解葡萄糖的总速度为４４１．６ＩＵ,当蔗糖浓度在０．２％以内时其反应速度与蔗糖浓度呈正相关（ｒ＝０．９９６）,使用半衰期１６２３次,在４℃下保存１２０天活力残存为８３．７％。     

甲基单胞菌Methylomonas sp.GYJ3中甲烷单加氧酶还原酶组分的纯化和性质

Ｍｅｔｙｌｏｍｏｎａｓｓｐ．ＧＹＪ３菌的甲烷单加氧酶（ＭＭＯ）粗酶提取液经ＤＥＡＥ－ＳｅｐｈａｒｏｓｅＣＬ－６Ｂ阴离子交换层析、ＳｅｐｈａｄｅｘＧ－１００凝胶过滤层析和ＤＥＡＥ－ＴＳＫｇｅｌＨＰＬＣ分离纯化出ＭＭＯ还原酶组分．经ＨＰＬＣ分析,纯度大于９５％,纯化倍数为４．４,加入至ＭＭＯ羟基化酶和调节蛋白Ｂ的体系中表现比活为２２８ｎｍｏｌ环氧丙烷每分钟毫克蛋白．ＳＤＳ－ＰＡＧＥ电泳表明还原酶由一种亚基组成,分子量４２ｋＤ．ＩＣＰ－ＡＥＳ测定还原酶的Ｆｅ含量为１．８３ｍｏｌＦｅ每ｍｏｌ蛋白．ＵＶ－Ｖｉｓ光谱表明还原酶除２８０ｎｍ蛋白质特征峰外在４６０ｎｍ有最大吸收峰,且Ａ２８０ｎｍ／Ａ４６０ｎｍ为２．５０,与其它黄素一铁硫蛋白相似,推测还原酶可能含一个ＦＡＤ辅基和Ｆｅ２Ｓ２中心．在厌氧条件下,还原酶能够和ＮＡＤＨ作用,ＵＶ－Ｖｉｓ光谱分析表明还原酶４６０ｎｍ处特征吸收峰消失,说明在ＭＭＯ催化过程中还原酶接受ＮＡＤＨ的电子．ＤＥＡＥ－ＳｅｐｈａｒｏｓｅＣＬ－６Ｂ阴离子交换层析分离出调节蛋白Ｂ,部分纯化的调节蛋白Ｂ的分子量大约在２０ｋＤ,它能够提高ＭＭＯ比活性４０倍,ＭＭＯ还原酶和调节蛋白Ｂ单独存在时不具有ＭＭＯ     

豆壳过氧化物酶的分离纯化及其性质研究

从豆壳抽提液经硫酸铵分级沉淀,ＤＥＡＥ－ＳｅｐｈａｄｅｘＡ－５０离子交换层析,ＣｏｎＡ－Ｓｅｐｈａｒｏｓｅ４Ｂ亲合层析和Ｂｉｏ－ＧｅｌＰ－６０凝胶过滤,纯化了豆壳过氧化物酶（ｓｏｙｂｅａｎｈｕｌｐｅｒ－ｏｘｉｄａｓｅ,ＳｈＰ）．纯化酶的比活力为７０７７Ｕ／ｍｇ,在ＳＤＳ－ＰＡＧＥ上显示出一条蛋白质带．ＳｈＰ分子量为３８０００,等电点为３．９;ＳｈＰ为一含血红素的糖蛋白,含糖量为１８．７％,光谱学分析揭示,在４０６ｎｍ处有一典型的Ｓｏｒｅｔ带,在５１０ｎｍ和６４０ｎｍ处有特征吸收峰．酶反应的最适ｐＨ在４．０附近,最适温度为４５℃;在ｐＨ２．５～１２．０之间较稳定,７５℃,保温６０ｍｉｎ,酶活力残余６８％,ＳｈＰ是一种良好的耐酸碱、耐热过氧化物酶．动力学分析求得ＳｈＰ的表观Ｋｍ（愈创木酚）为１．６２ｍｍｏｌ／Ｌ,表现Ｋｍ（Ｈ２Ｏ２）为０．３４ｍｍｏｌ／Ｌ．在所测定的化学试剂中,Ｎ－３、ＣＮ－、Ｆｅ３＋、Ｆｅ２＋和Ｓｎ２＋对酶有较强烈的抑制作用,而重金属离子Ａｇ＋、Ｈｇ２＋、Ｐｂ２＋、Ｃｕ２＋、Ｃｒ３＋以及ＳＤＳ和ＥＤＴＡ对酶活力无显著影响     

黑曲霉ρ-葡萄糖甘酶的提纯与性质

从黑曲霉Ａｓｐｅｒｇｉｌｕｓｎｉｇｅｒ发酵液中分离提纯了β－葡萄糖苷酶。提纯步骤通过（ＮＨ４）２ＳＯ４分级沉淀,ＤＥＡＥ－ＳｅｐｈａｄｅｘＡ－５０和ＳｅｐｈａｄｅｘＧ－１００等三步纯化,得到凝胶电泳均一的β－葡萄糖苷酶。该酶的最适ｐＨ４．５,最适温度６０℃,Ｋｍ为０．４４（ＮＰＧ）,并有较好的热稳定性。用ＳＤＳ－凝胶电泳法和凝胶色谱法测得该酶的分子量为１２００００     

单宁酶的固定化及其在酯型儿茶素水解反应中的应用

采用自制的壳聚糖为载体对单宁酶（ＴＡ）固定化,ＴＡ与壳聚糖配比１：２．５,３０℃固定２ｈ,活力回收达２３．６％～３３．１％;偶联效率为８４．９％～８８．０％。固定化单宁酶（ＩＴＡ）的表观Ｋｍ值（以没食子酸丙酯为底物）为２２．２×１０－６ｍｏｌ／Ｌ,ＴＡ的Ｋｍ值（以没食子酸丙酯为底物）为１０×１０－６ｍｏｌ／Ｌ,ＴＡ和ＩＴＡ的最适反应温度分别为４０℃和５０℃;６０℃处理１５ｍｉｎ,残存活性分别为１３．６％和６０．３％。ＴＡ和ＩＴＡ的最适ｐＨ值分别为５．８和６．４;ＴＡ在ｐＨ４．８～７．８活力稳定,而ＩＴＡ活力稳定范围在ｐＨ４．８～６．８．ＩＴＡ作用于ＥＧＣＧ的半衰期为７８．７ｈ,ＥＧＣＧ水解率达９０．３％。对茶多酚提取物进行水解,其所含的酯型儿茶素ＥＧＣＧ和ＥＣＧ水解率分别为９６．４％和９６．８％,非酯型儿茶素ＥＧＣ和ＥＣ的含量显著增加。     

单宁酶的固定化及其在酯型儿茶素水解反应中的应用

采用自制的壳聚糖为载体对单宁酶（ＴＡ）固定化,ＴＡ与壳聚糖配比１：２．５,３０℃固定２ｈ,活力回收达２３．６％￣３３．１％;偶联效率为８４．９％￣８８．０％。固定化单宁酶（ＩＴＡ）的表观Ｋｍ值（以没食子酸丙酯为底物）为２２．２×１０＾－６ｍｏｌ／Ｌ,ＴＡ的Ｋｍ值（以没食子酸丙酯为底物）为１０×１０＾－６ｍｏｌ／Ｌ,ＴＡ和ＩＴＡ的最适反应温度分别为４０℃和５０℃;６０℃处理１５ｍｉｎ,残存活性分别为     

无花果蛋白酶在阴离子交换树脂上的固定化

无花果蛋白酶通过８％戊二醛活化载体,共价结合到聚苯乙烯阴离子交换树脂ＧＭ２０１上,固定化作用在ｐＨ７．７,酶浓度０．８ｍｇ／ｇ树脂,４℃下进行６ｈ。得到的固定化酶表观Ｋ_ｍ值（酪蛋白,１．１１×１０~（－４）ｍｏｌ／Ｌ）小于溶液酶Ｋ_ｍ值（１．９６×１０~（－４）ｍｏｌ／Ｌ）;固定化酶活性在ｐＨ６～８保持稳定,溶液酶最适ｐＨ为７．２;固定化酶最适温度由溶液酶的５０～６０℃移至３７℃;固定化酶２５℃保持７ｄ,重复水解酪蛋白７次后,保留８３．３％活性。固定化酶对酪蛋白水解度达４７．５％,对大豆球蛋白达１１．６％。     

乳酶克鲁维酵母β—半乳糖苷酶的分离纯化及性质研究

乳酸克鲁维酵母经高压破壁后的粗提液,其β－半乳糖苷酶比活力为５．５６ｕ／ｍｇ．经硫酸铵沉淀,丙酮沉淀,ＰＡＰＭＡ－Ａｅｐｈａｒｏｓｅ ４Ｂ柱层析后,乳糖酶比活力达３７０ｕ／ｍｇ,纯化了６６．２倍,ＳＤＳ－ＰＡＧＥ鉴定为一条带,分子量８５０００Ｄａ。酶作用的最适ｐＨ在６．４－６．８之间,最适温度４０℃,５０℃保温１５ｍｉｎ酶活丧失９０％,以邻硝基苯－β－半乳糖苷为底物的米氏常数为２．７８ｍｍｏｌ／Ｌ     

人胃腺苷脱氨酶的分离纯化及性质研究

用硫酸铵分级沉淀、ＤＥＡＥ－纤维素离子交换层析、免疫亲和层析、ＳｅｐｈａｄｅｘＧ１００凝胶柱层析从人胃组织中提取出腺苷脱氨酶,酶纯化１９３２４倍,比活力为５７９７Ｕ／ｍｇ蛋白．提取酶液经ＰＡＧＥ、ＳＤＳ－ＰＡＧＥ和等电聚焦只呈现一条区带。测得该酶的分子量为４１．２ｋＤ,等电点为ｐＨ４．８．氨基酸组成分析表明该酶由３８８个氨基酸残基组成,Ｎ端氨基酸为精氨酸。酶的最适ｐＨ为６．５,ｐＨ小于５．０或大于９．０时不稳定;最适温度为３７℃,对热不太稳定,以腺苷及２－脱氧腺苷作为底物,其Ｋｍ分别为８７μｍｏｌ／Ｌ和４１μｍｏｌ／Ｌ。     

胞外青霉素酰化酶的纯化及部分理化性质

巨大芽孢杆菌产胞外青霉素酰化酶发酵液经硫酸铵分级抽提及Ｓｅｐｈａｄｅｘ Ｇ－１００、羟基磷灰石、ＤＥＡＥ－纤维素ＤＥ５２等层析步,提纯了青霉素酰化酶,得到电泳均一的酶制剂,纯酶比活力约为２５Ｕ／ｍｇ蛋白,纯化４９倍,活力回收５８％,经ＰＡＧＥ及ＳＤＳ－ＰＡＧＥ测知该酶不含亚基,其分子量约为１４０ｋＤ。该酶最适ｐＨ为９．０,最适温度４７℃,用底物ＮＩＰＡＢ测活,其Ｋｍ值为６．２×１０＾－４ｍｏｌ／Ｌ     

Rat liver cytochrome P-450b, P-420b, and P-420c are degraded to biliverdin by heme oxygenase

In this report we provide data, for the first time, demonstrating the conversion of the heme moiety of certain cytochrome P-450 and P-420 preparations, to biliverdin, catalyzed by heme oxygenase. We have used purified preparations of cytochromes P-450c, P-450b, P-450/P-420c, or P-450/P-420b as substrates in a heme oxygenase assay system reconstituted with heme oxygenase isoforms, HO-2 or HO-1, NADPH-cytochrome c (P-450) reductase, biliverdin reductase, NADPH, and Emulgen 911. With cytochrome P-450b or P-450/P-420b preparations, a near quantitative conversion of degraded heme to bile pigments was observed. In the case of cytochrome P-450/P-420c approximately 70% of the degraded heme was accounted for as bilirubin but only cytochrome P-420c was appreciably degraded. The role of heme oxygenase in this reaction was supported by the following observations: (i) bilirubin formation was not observed when heme oxygenase was omitted from the assay system; (ii) the rate of degradation of the heme moiety was at least threefold greater with heme oxygenase and NADPH-cytochrome c (P-450) reductase than that observed with reductase alone; and (iii) the presence of Zn- or Sn-protoporphyrins (2 microM), known competitive inhibitors of heme oxygenase, resulted in 70-90% inhibition of bilirubin formation.     

Spectroscopic characterization of a higher plant heme oxygenase isoform-1 from Glycine max (soybean)--coordination structure of the heme complex and catabolism of heme

Heme oxygenase converts heme into biliverdin, CO, and free iron. In plants, as well as in cyanobacteria, heme oxygenase plays a particular role in the biosynthesis of photoreceptive pigments, such as phytochromobilins and phycobilins, supplying biliverdin IX(alpha) as a direct synthetic resource. In this study, a higher plant heme oxygenase, GmHO-1, of Glycine max (soybean), was prepared to evaluate the molecular features of its heme complex, the enzymatic activity, and the mechanism of heme conversion. The similarity in the amino acid sequence between GmHO-1 and heme oxygenases from other biological species is low, and GmHO-1 binds heme with 1 : 1 stoichiometry at His30; this position does not correspond to the proximal histidine of other heme oxygenases in their sequence alignments. The heme bound to GmHO-1, in the ferric high-spin state, exhibits an acid-base transition and is converted to biliverdin IX(alpha) in the presence of NADPH/ferredoxin reductase/ferredoxin, or ascorbate. During the heme conversion, an intermediate with an absorption maximum different from that of typical verdoheme-heme oxygenase or CO-verdoheme-heme oxygenase complexes was observed and was extracted as a bis-imidazole complex; it was identified as verdoheme. A myoglobin mutant, H64L, with high CO affinity trapped CO produced during the heme degradation. Thus, the mechanism of heme degradation by GmHO-1 appears to be similar to that of known heme oxygenases, despite the low sequence homology. The heme conversion by GmHO-1 is as fast as that by SynHO-1 in the presence of NADPH/ferredoxin reductase/ferredoxin, thereby suggesting that the latter is the physiologic electron-donating system.     

Heme oxygenase-1-derived carbon monoxide stimulates adenosine triphosphate generation in human hepatocyte

Heme oxygenases cleave the pro-oxidant heme molecule into carbon monoxide, ferrous iron, and biliverdin, which is subsequently converted to bilirubin. Increasing the enzymatic activities of heme oxygenase by expression of its inducible isoform, heme oxygenase-1, protects hepatocyte from apoptosis. In the present study, we investigated the mechanisms involving in heme oxygenase-1-mediated cytoprotection. Heme oxygenase-1 could induce the expression of anti-apoptotic protein-Bcl-xL in human hepatocyte. This effect is associated with the activation of p38 MAPK signaling pathway. Carbon monoxide derived from heme oxygenase activities significantly increased adenosine triphosphate levels in hepatocyte that was essential for potentiation of the activation of p38 MAPK signaling. Our demonstration of the importance of the energy status to maximize an anti-apoptotic response provides a new insight into HO-mediated cytoprotection.     

Purification and characterization of heme oxygenase from chick liver. Comparison of the avian and mammalian enzymes

A major inducible form of heme oxygenase (EC 1.14.99.3) was purified from liver microsomes of chicks pretreated with cadmium chloride. The purification involved solubilization of microsomes with Emulgen 913 and sodium cholate, followed by DEAE-Sephacel, carboxymethyl-cellulose (CM-52) and hydroxyapatite chromatography, and FPLC through Superose 6 and 12 columns operating in series. The final product gave a single band on silver-stained SDS/polyacrylamide gels (Mr = 33,000). Optimal conditions for measurement of activity of solubilized heme oxygenase were studied. In a reconstituted system containing purified heme oxygenase, NADPH-cytochrome reductase, biliverdin reductase and NADPH, the Km for free heme was 3.8 +/- 0.5 microM; for heme in the presence of bovine serum albumin (5 mol heme/3 mol albumin) the Km was 5.0 +/- 0.8 microM; and the Km for NADPH was 6.1 +/- 0.4 microM (all values mean +/- SD, n = 3). Oxygen concentration as low as 15 microM, with saturating concentrations of heme and NADPH, did not affect the reaction rate, indicating that the supply of oxygen is not involved in the physiological regulation of activity of the enzyme. The pH optimum of the reaction was 7.4; at 37 degrees C, the apparent Vmax was 580 +/- 44 nmol biliverdin.(mg protein)-1.min-1 and the molecular activity was 19.2 min-1. Biliverdin IXa was the sole biliverdin isomer formed. In the presence of purified biliverdin reductase, biliverdin was converted quantitatively to bilirubin. Addition of catalase to the reconstituted system decreased the breakdown of heme to non-biliverdin products and led to nearly stoichiometric conversion of heme to biliverdin. Activity of the enzyme in the reconstituted system was inhibited by metalloporphyrins in the following order of decreasing potency: tin mesoporphyrin greater than tin protoporphyrin greater than zinc protoporphyrin greater than manganese protoporphyrin greater than cobalt protoporphyrin. Protoporphyrin (3.3 or 6.6 microM) (and several other porphyrins) and metallic ions (100 microM) alone had little if any inhibitory effect, except for Hg2+ which inhibited by 67% at 10 microM and totally at 15 microM. Following partial cleavage, fragments of the purified enzyme were sequenced. Comparison of sequences to those derived from cDNA sequences for the major inducible rat and human heme oxygenase showed 69% and 76% similarities, respectively. The histidine residue at position 132 of rat heme oxygenase-1 and the residues (Lys128-Arg136) flanking His132 were conserved in all three enzymes, as well as in the corresponding portion of a fourth less highly similar rat enzyme, heme oxygenase-2.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fractionation of erytroblasts with affinitymediated modifications of their electrical properties using counter-current distribution

Enterally administered, heme is a good source of iron in humans and other animals, but the metabolism of heme by enterocytes has not been fully characterized. Caco-2 cells in culture provide a useful model for studying cells that resemble small intestinal epithelium, both morphologically and functionally. In this paper we show that heme oxygenase, the rate-controlling enzyme of heme catabolism, is present in abundance in Caco-2 cells, and that levels of its mRNA and activity can be increased by exposure of the cells to heme or metal ions (cadmium, cobalt). Caco-2 cells also contain biliverdin reductase activity which, in the basal state, is similar to that of heme oxygenase (approximately 40 pmole of product per mg protein per minute); however, when heme oxygenase is induced, biliverdin reductase may become rate-limiting for bilirubin production.Abbreviations BVR biliverdin reductase - DMEM Dulbecco's modified Eagles medium - DMSO dimethyl sulfoxide - HO heme oxygenase - 1xSSC a solution of 0.015 M sodium citrate/0.15 sodium chloride     

Decreased activity of the antioxidant heme oxygenase enzyme: implications in ischemia and in Alzheimer's disease

Heme oxygenase (HO) is the rate-limiting enzyme for the degradation of heme, a prooxidant, coming from a multitude of heme-containing proteins/enzymes. With the action of cytochrome P₄₅₀ reductase, HO cleaves the heme ring into biliverdin which is converted into bilirubin, both have been shown to have intrinsic radical scavenger activities. Iron is also released from the heme core and in its free form can act as a catalyst for oxidative stress damage or can be sequested by several iron-binding proteins. Under physiological conditions, the newly generated iron can be neutralized within the cell. The third product of the opening of the porphyrin ring is carbon monoxide, which role has been puzzling. It has been reported as a potential neuromodulator, it modulates guanylate cyclase activity and has vasodilation, anti-inflammatory and antiapoptotic effects. In the brain, HO2 accounts for the vast majority of HO activity. By decreasing HO2 activity, one would expect more neuronal damage after oxidative stress injury with possible direct implications to acute and chronic neurodegenerative disorders. Pharmacological ways to increase neuronal HO activity is likely to have therapeutic applications.     

Heme oxygenase and the kidney

Heme plays a significant pathogenic role in several diseases involving the kidney. The cellular content of heme, derived either from the delivery of filtered heme proteins such as hemoglobin and myoglobin, or from the breakdown of ubiquitous intracellular heme proteins, is regulated via the heme oxygenase enzyme system. Heme oxygenases catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Three isoforms of heme oxygenase (HO) enzyme have been described: an inducible isoform, HO-1, and two constitutively expressed isoforms, HO-2 and HO-3. Induction of HO-1 occurs as an adaptive and beneficial response to several injurious stimuli, and has been implicated in many clinically relevant disease states including atherosclerosis, transplant rejection, endotoxic shock, hypertension, acute lung injury, acute renal injury, as well as others. This review will focus predominantly on the role of HO-1 in the kidney.     

Variation of the oxidation state of verdoheme in the heme oxygenase reaction

Heme oxygenase (HO) converts hemin to biliverdin, CO, and iron applying molecular oxygen and electrons. During successive HO reactions, two intermediates, α-hydroxyhemin and verdoheme, have been generated. Here, oxidation state of the verdoheme-HO complexes is controversial. To clarify this, the heme conversion by soybean and rat HO isoform-1 (GmHO-1 and rHO-1, respectively) was compared both under physiological conditions, with oxygen and NADPH coupled with ferredoxin reductase/ferredoxin for GmHO-1 or with cytochrome P450 reductase for rHO-1, and under a non-physiological condition with hydrogen peroxide. EPR measurements on the hemin-GmHO-1 reaction with oxygen detected a low-spin ferric intermediate, which was undetectable in the rHO-1 reaction, suggesting the verdoheme in the six-coordinate ferric state in GmHO-1. Optical absorption measurements on this reaction indicated that the heme degradation was extremely retarded at verdoheme though this reaction was not inhibited under high-CO concentrations, unlike the rHO-1 reaction. On the contrary, the Gm and rHO-1 reactions with hydrogen peroxide both provided ferric low-spin intermediates though their yields were different. The optical absorption spectra suggested that the ferric and ferrous verdoheme coexisted in reaction mixtures and were slowly converted to the ferric biliverdin complex. Consequently, in the physiological oxygen reactions, the verdoheme is found to be stabilized in the ferric state in GmHO-1 probably guided by protein distal residues and in the ferrous state in rHO-1, whereas in the hydrogen peroxide reactions, hydrogen peroxide or hydroxide coordination stabilizes the ferric state of verdoheme in both HOs.     

Degradation of heme in gram-negative bacteria: the product of the hemO gene of Neisseriae is a heme oxygenase

A full-length heme oxygenase gene from the gram-negative pathogen Neisseria meningitidis was cloned and expressed in Escherichia coli. Expression of the enzyme yielded soluble catalytically active protein and caused accumulation of biliverdin within the E. coli cells. The purified HemO forms a 1:1 complex with heme and has a heme protein spectrum similar to that previously reported for the purified heme oxygenase (HmuO) from the gram-positive pathogen Corynebacterium diphtheriae and for eukaryotic heme oxygenases. The overall sequence identity between HemO and these heme oxygenases is, however, low. In the presence of ascorbate or the human NADPH cytochrome P450 reductase system, the heme-HemO complex is converted to ferric-biliverdin IXalpha and carbon monoxide as the final products. Homologs of the hemO gene were identified and characterized in six commensal Neisseria isolates, Neisseria lactamica, Neisseria subflava, Neisseria flava, Neisseria polysacchareae, Neisseria kochii, and Neisseria cinerea. All HemO orthologs shared between 95 and 98% identity in amino acid sequences with functionally important residues being completely conserved. This is the first heme oxygenase identified in a gram-negative pathogen. The identification of HemO as a heme oxygenase provides further evidence that oxidative cleavage of the heme is the mechanism by which some bacteria acquire iron for further use.     

Generation of bile pigments by haem oxygenase: a refined cellular strategy in response to stressful insults

The family of haem oxygenase enzymes is unique in nature for its role in haem degradation. Haem is cleaved at the alpha-meso position by haem oxygenase with the support of electrons donated by cytochrome P450 reductase, the first products of this reaction being CO, iron and biliverdin. Biliverdin is then converted to bilirubin by biliverdin reductase. If haem is viewed as a substrate for an anabolic pathway, it becomes evident that haem oxygenases do not break down haem for elimination from the body, but rather use haem to generate crucial molecules that can modulate cellular functions. The facts that biliverdin and bilirubin are potent antioxidants and that CO is both a vasoactive and signalling molecule sustain this idea. The existence of a constitutive haem oxygenase (HO-2), mainly present in the vasculature and nervous system, and an inducible haem oxygenase (HO-1), which is highly expressed during stress conditions in all tissues, also suggests that cells have evolved a fine control of this enzymic pathway to ultimately regulate haem consumption and to ensure production of CO, biliverdin/bilirubin and iron during physiological and pathophysiological situations. This review will focus primarily on the biological actions of biliverdin and bilirubin derived from the haem oxygenase/biliverdin reductase systems and their potential roles in counteracting oxidative and nitrosative stress.