摘要:

AbstractHeme serves as the prosthetic group of various hemoproteins that carry out many essential functions for cells. For example, the transport of oxygen is carried out by hemoglobin and myoglobin; electron transport depends on the function of various mitochondrial cytochromes; oxidative metabolism in a number of xenobiotic substances and endogenous steroid hormones, vitamins and fatty acids are catalyzed by the activity of the microsomal cytochrome P450. In addition, heme is involved in the translation of proteins, and is required in certain aspects of cell development and differentiation. Inherited and acquired enzymatic defects in heme biosynthesis result in clinical conditions termed the porphyrias. Patients with porphyria express various difficulties in these functions as neurological disturbances, abnormal drug metabolism, and/or skin photosensitivity. Recent advances in this field have shed much light on the genetic, enzymological and clinical aspects of heme synthesis, catabolism and inherited defects of these enzymes.

ISSN:1066-5099    

DOI:10.1002/stem.5530120704

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractTwo distinct patterns of regulating heme biosynthesis have been observed in animals: while heme negatively regulates the synthesis of δ‐aminolevulinate (ALA) synthase in non‐erythroid cells, the expression of the enzyme is regulated developmentally in red blood cells. This observation eventually led to the cloning of both a tissue‐specific ALA synthase isozyme (ALAS‐E) that is expressed in erythroid‐lineage cells and is distinct from the housekeeping isozyme (ALAS‐N). We originally isolated cDNA clones encoding chicken ALAS‐E by the combined use of an anti‐chicken ALAS‐N antibody, which was partially cross‐reactive to chicken ALAS‐E, and a λgt11 expression library. ALAS‐E was also purified to homogeneity from rat reticulocyte lysate using a papain digestion method. The papain‐resistant core catalytic domain overlaps with the evolutionarily conserved segment that had been described by sequence alignment of ALA synthases from a variety of species, suggesting that the papain‐resistant domain represents the ancestral core of the enzyme. Blot hybridization analysis of RNA isolated from various developmental stage rat livers and from chicken and mouse erythroleukemia cells demonstrated that ALAS‐E is the key enzyme which supplies large quantities of heme for hemoglobin synthesis. We are currently investigating the mechanisms which confer erythroid‐specific transcriptional activation of the ALAS‐E gene through transient transfection assays in erythroid cells using human and chicken ALAS‐E genes. These experiments have identified promoter elements which are required for high level, erythroi

ISSN:1066-5099    

DOI:10.1002/stem.5530120705

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstractδ‐Aminolevulinate (ALA) dehydratase is the second enzyme of the heme biosynthetic pathway. In mammals, ALA dehydratase is more active in the liver and erythroid cells than ALA synthase, the rate limiting step of heme synthesis in liver. Nevertheless, decreases in ALA dehydratase activity by chemical intoxication as well as by genetic disorders are known to suppress heme biosynthesis. In this report, we describe a) a comparison of the properties of ALA dehydratase from various species, b) gene activation of ALA dehydratase and the other heme enzymes during erythroid differentiation, c) the gene structure of ALA dehydratase and expression of mRNA encoding erythroid‐specific and nonspecific isoforms, and d) toxicologic and genetic mechanisms that may reduce ALA dehydratase acti

ISSN:1066-5099    

DOI:10.1002/stem.5530120706

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractFerrochelatase (heme synthase, protoheme ferrolyase [EC 4.99.1.1]), the final enzyme of the heme biosynthetic pathway, catalyzes the insertion of ferrous ion into protoporphyrin IX to produce protoheme IX. The thorough understanding of the enzyme is prerequisite to elucidating the regulation of iron and heme metabolism. The enzyme's activity is found on the inner mitochondrial membrane of a variety of mammalian cells. The enzyme catalyzes the chelation not only of iron but also of divalent metal ions including cobalt and zinc, and the activity is affected by various metals and lipids. The molecular weights of eukaryotic ferrochelatases are 40,000‐42,000 daltons. Complementary DNA (cDNA) encoding ferrochelatase from mouse, human, yeast and bacteria have been isolated, and the derived amino acid sequences show 27‐88% homologies among species. The expression of ferrochelatase seems to occur in all living cells, and to play an important role in the regulation of heme biosynthesis. Ferrochelatase is markedly induced at the transcriptional level during erythroid differentiation when iron uptake by cells and hemoglobin synthesis are upregulated. This induction can be explained by the existence of sequences characteristic of erythroid‐related genes. The gene has been mapped to human chromosome 18q21.3 and contains 11 exons with a size of about 45 kilobases. Once the gene for human ferrochelatase is cloned, the molecular basis and clinical diagnosis of erythropoietic protoporphyria, caused by a deficiency of ferrochelatase, will become possible. This review summarizes recent advances in ferrochelatase research and suggests important subjects for future res

ISSN:1066-5099    

DOI:10.1002/stem.5530120707

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the latent period of the induction of murine erythroleukemia (MEL) cell differentiation,c‐mycmRNA levels show a drastic change. The elevated expression of a transfectedc‐mycgene inhibits the commitment and terminal differentiation of MEL cells,c‐mycregulates commitment and differentiation by means of its different functional domains: almost all regions are required for inhibition of commitment, whereas domains II and IV are required for inhibition of terminal differentiation.c‐mycmay regulate commitment and differentiation by interacting with proteins through different domains. In addition to differential regulation of the latent‐period genes, overexpression ofc‐mycrepresses the expression of glycophorin, globin and δ‐aminolevulinic acid synthase‐erythroid (ALAS‐E) genes, but it has no effect on the expression of GATA‐1 and erythropoietin receptor (EpoR) genes. A possible mechanism for the coordinated regulation of globin and heme sy

ISSN:1066-5099    

DOI:10.1002/stem.5530120708

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNon‐enzymatic glycation of protein is a chemical modification reaction often found in human metabolism. Glycated hemoglobin (HbA1c) has been used as a model protein for studying non‐enzymatic glycation because of its biological significance. Several questions have been raised in the course of studying this important biological reaction. Among them, we have focused on two major questions: 1) Why is the amino‐terminus of the β‐chain of human hemoglobin (HbA) a preferred target and not the amino‐terminus of the α‐chain, since HbA has Val residues in both its amino‐termini? 2) Why do some Schiff base intermediates advance Amadori rearrangement but not others?Since non‐enzymatic glycation is a rather slow process, biochemical analysis is often difficult; a model system which mimics the chemistry of non‐enzymatic glycation with a faster reaction rate has been developed. The model system using glycer‐aldehyde with amino acids or peptides has demonstrated that the presence of a His‐2(β) residue contributes significantly to the formation of HbA1c. Such a positively charged group is found at or near the glycation sites in many other non‐enzymatically glycosylated proteins. Thus, it is feasible to assume a unique role for the positively charged residue in non‐en

ISSN:1066-5099    

DOI:10.1002/stem.5530120709

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe P450 superfamily is a large group of hemoprotein monooxygenases participating in the oxidation of various small molecules. Numerous species of P450 showing various substrate specificities exist in a wide variety of organisms and play significant roles in various metabolic pathways including biosynthesis of biosignal substances and secondary metabolites, degradation of toxic xenobiotics, and adaptive assimilation of unusual carbon sources. The divergence of an ancestral P450 into multiple monooxygenases expanded the ability of living organisms to metabolize small molecules. Most P450 monooxygenases are inducible enzymes, and the factors regulating their expression are as varied as their substrates. Thus, P450 enzymes are versatile hemoproteins not only in their metabolic functions but also in their regulation of gene activation. Such versatility among P450 enzymes is essential for living organisms to adapt to diverse environments.

ISSN:1066-5099    

DOI:10.1002/stem.5530120710

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractCytochrome P450 (CYP) isozymes have been cloned from various tissues and species and form the cytochrome P450 superfamily. We have isolated cytochrome P450 C‐M/F, which we regard as a major form of the constitutive cytochrome P450 isozyme. Cytochrome P450 C‐M/F was highly active in the 2‐ and 16α‐hydroxylation of estrogens, as well as in the N‐demethylation of ethyl‐morphine and benzphetamine. It was essentially uninducible by phenobarbital, 3‐methylcholan‐threne or β‐naphthoflavone. Immunochemical studies demonstrated the presence of cytochrome P450 C‐M/F in the liver of male and female rats and in the kidney of male rats. This is consistent with P450 C‐M/F activity towards estrogens, since they are metabolized in the liver and kidney and excreted into the urine.Highly similar genes were identified by immunoscreening, and comprised the CYP2D sub‐family. Five genes—CYP2D1, CYP2D2, CYP2D3, CYP2D4 and CYP2D5—have been isolated from rats. In spite of the high similarity, there is an obvious difference in substrate specificity between even the most similar isozymes. Among allelic variants reported for CYP2D1 and CYP2D2, P450IID1v is a mutant with decreased activity specifically towards bufuralol, due to a single amino acid substitution.Biochemical studies have demonstrated enzyme activities of CYP2D1 and CYP2D2 isozymes, while those of CYP2D3, CYP2D4 and CYP2D5 remain unknown. It is suggested that CYP2D isozymes play a role in maintaining homeostasis of the organism since they are constitutively expressed in the livers of both sexes and in the kidneys of males. Understanding their endogenous substrates shoul

ISSN:1066-5099    

DOI:10.1002/stem.5530120711

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe microbicidal oxidase of phagocytes, upon activation, reduces molecular oxygen to superoxide in conjunction with the oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH). The terminal component of the oxidative cascade is cytochromeb558consisting of 91 kDa (gp91‐phox) and 22 kDa (p22‐phox) subunits with heme acting as the electron carrier to oxygen. However, the NADPH‐binding flavoprotein that transports electrons from the substrate to the cytochrome has not been identified. Alignment of the amino acid sequence of gp91‐phoxwith that of previously characterized flavoproteins suggests that this subunit contains both the NADPH‐and flavin adenine dinucleotide (FAD)‐binding domains. Several lines of experimental evidence strongly support this proposal. Thus cytochromeb558is regarded as the first example of a flavocytochrome in higher eukaryotes, comprising the complete electron transporting machinery of phagocyte NA

ISSN:1066-5099    

DOI:10.1002/stem.5530120712

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractHeme oxygenase is an essential enzyme in heme catabolism that cleaves heme to form biliverdin, releasing carbon monoxide and iron. In mammals, biliverdin is subsequently converted to bilirubin by biliverdin reductase. There are two isozymes of heme oxygenase: heme oxygenase‐1 (HO‐1) and heme oxygenase‐2 (HO‐2), each of which is encoded by a separate gene. Both isozymes share a significant similarity in amino acid sequence and catalyze heme breakdown under similar conditions. However, both enzymes are regulated in distinct manners: specifically, HO‐1 is inducible by various environmental factors including its own substrate heme, while HO‐2 is not inducible at all. Moreover, there has been remarkable progress concerning the physiological roles of the heme catabolites carbon monoxide (CO) and bilirubin, which had previously been considered mere toxic waste products. However, CO was suggested to function as a potential signaling gas, and bilirubin was shown to be an effective radical scavenger under physiological conditions. Thus, the inducibility of HO‐1 may represent an important biological response. In this review, the general properties of heme oxygenase are briefly described with emphasis on the current findings regarding the regulation of heme oxygenase ge

ISSN:1066-5099    

DOI:10.1002/stem.5530120713

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY