ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The Omega class glutathione transferases (GSTs) have been identified in many organisms, including human, mouse, rat, pig,Caenorhabditis elegansandDrosophila melanogaster. These GSTs have poor activity with common GST substrates, but exhibit novel glutathione-dependent thioltransferase, dehydroascorbate reductase and monomethylarsonate reductase activities, and modulate Ca2+release by ryanodine receptors. An investigation of the genomic organization of humanGSTO1identified a second actively transcribed member of the Omega class (GSTO2). BothGSTO1andGSTO2are composed of six exons and are separated by 7.5 kb on chromosome 10q24.3. A third sequence that appears to be a reverse-transcribed pseudogene (GSTO3p) has been identified on chromosome 3. GSTO2 has 64% amino acid identity with GSTO1 and conserves the cysteine residue at position 32, which is thought to be important in the active site of GSTO1. Expression of GSTO2 mRNA was seen in a range of tissues, including the liver, kidney, skeletal muscle and prostate. The strongest GSTO2 expression was in the testis, which also expresses a larger transcript than other tissues. Characterization of recombinant GSTO2 has been limited by its poor solubility. Two functional polymorphisms ofGSTO1have been identified. One alters a splice junction and causes the deletion of E155 and another results in an A140D substitution. Characterization of these variants revealed that the A140D substitution affects neither heat stability, nor activity towards 1-chloro-2,4-dinitrobenzene or hydroxyethyl disulphide. In contrast, deletion of residue E155 appears to contribute towards both a loss of heat stability and increased enzymatic activity.

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

A genetic dimorphism encodes for either alanine (Ala) or valine (Val) in the mitochondrial targeting sequence (MTS) of human manganese superoxide dismutase (MnSOD) and has been reported to modulate the risk of some cancers, neurodegenerative diseases and severe alcoholic liver disease. Although functional consequences of this dimorphism on MnSOD activity have not been assessed, computer models predict a partial α-helix structure for the Ala-MnSOD/MTS, but a β-sheet structure for the Val-variant, which could hamper mitochondrial import. To investigate this hypothesis, we studied the in-vitro import of chimaeric proteins composed of either one of the MnSOD/MTS fused to the mouse dihydrofolate reductase (DHFR) protein, and the import of the two human MnSOD precursor variants into rat liver mitochondria. Compared to Ala-proteins, the Val-MnSOD/MTS-DHFR precursor and Val-MnSOD precursor were both partly arrested within the inner mitochondrial membrane. The Ala-MnSOD precursor generated 30–40% more of the active, matricial, processed MnSOD homotetramer than the Val-MnSOD precursor. These results show that the Ala-MnSOD/MTS allows efficient MnSOD import into the mitochondrial matrix, while the Val-variant causes partial arrest of the precursor within the inner membrane and decreased formation of the active MnSOD tetramer in the mitochondrial matrix.

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Arylamine carcinogens induce prostate tumours in rodent models and may contribute to the aetiology of human prostate cancers.N-acetylation andO-acetylation, catalysed byN-acetyltransferase 1 (NAT1) and 2 (NAT2), activate and/or deactivate arylamines to electrophilic intermediates that bind DNA and initiate tumours in target organs. NAT1 and NAT2 are both subject to genetic polymorphism in humans, and molecular epidemiological investigations suggest thatNAT1and/orNAT2acetylator genotype modifies risk for prostate cancers. A Syrian hamster model congenic at theNAT2locus was used to investigate the role ofNAT2acetylator genotype inN- andO-acetylation of aromatic and heterocyclic amine carcinogens in the liver and prostate. A gene dose–response (NAT2*15/*15>NAT2*15/*16A>NAT2*16A/*16A) relationship was observed in liver and prostate cytosol towards theN-acetylation ofp-aminobenzoic acid, 2-aminofluorene, beta-napthylamine, 4-aminobiphenyl, and 3,2′-dimethyl-4-aminobiphenyl. NAT1 and NAT2 were separated and partially purified from liver and prostate cytosol. NAT1 and NAT2 in liver and prostate catalysedN-acetylation of the arylamines above andO-acetylation ofN-hydroxy derivatives of 2-aminofluorene, 4-aminobiphenyl and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. Rates were higher in rapid versus slow acetylators when catalysed by NAT2 but not when catalysed by NAT1. Partially purified prostate NAT2 exhibited higher apparentKmandVmaxthan NAT1. ProstateNAT1mRNA levels were higher thanNAT2and neitherNAT1norNAT2mRNA level differed withNAT2acetylator genotype. The results provide mechanistic support for a role ofNAT1and/orNAT2acetylator polymorphism(s) in human prostate cancer risk related to aromatic and/or heterocyclic amine carcinogens.

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Clozapine is an atypical antipsychotic drug that is metabolized to a major extent by the cytochrome P450 enzyme CYP1A2. Smoking is a potent inducer of CYP1A2 enzyme activity, resulting in significant lower clozapine serum concentrations in smokers compared with non-smokers, upon a given dose. Recently, a single nucleotide polymorphism identified at position 734 of theCYP1A2gene, was reported to affect the inducibility of the enzyme. Because this polymorphism in relation to smoking behaviour may be relevant in treatment with clozapine, we studied the effect ofCYP1A2genotype on clozapine clearance and dose requirement in a group of 80 smoking and non-smoking schizophrenic patients on long-term clozapine therapy. Clozapine serum concentration andCYP1A2genotype had been determined routinely by high-performance liquid chromatography and polymerase chain reaction analyses, respectively. In smokers, the clozapine serum concentration corrected for dose (C/D ratio) was on average 2.5 times lower compared with non-smokers, indicating an enhanced clearance. The mean required maintenance doses of clozapine for smokers and non-smokers were 382 mg/day and 197 mg/day, respectively (P<0.01). Neither among smokers, nor among non-smokers mean C/D ratios and daily doses did vary significantly between patients with the differentCYP1A2genotypes. The results show that clozapine clearance and daily dose requirement are strongly associated with smoking behaviour, while theCYP1A2genetic polymorphism seems to have no significant clinical effect. Dosage adjustment based on smoking behaviour would be of value in order to lower the incidence of non-therapeutic serum drug levels and, consequently, intoxication or inadequate antipsychotic response.

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Polymorphic cytochrome P450 2D6 (CYP2D6) is expressed in several types of central neurons but its function in human brain is currently unknown. Using recombinant enzymes andCYP2D6-transgenic mice, we established that 5-methoxytryptamine (5-MT), a metabolite and precursor of melatonin, is a specific and high-turnover endogenous substrate of CYP2D6. This potent serotonergic neuromodulator in numerous physiological systems binds tightly to recombinant CYP2D6 enzyme with an equilibrium dissociation constant (Ks) of 23.4 μmol/l, and isO-demethylated to serotonin (5-hydroxytryptamine, 5-HT) with a high turnover of 51.7 min−1and low Michaelis–Menten constant of 19.5 μmol/l. The production of 5-HT from 5-MT catalyzed by CYP2D6 was inhibited by selective serotonin reuptake inhibitors, and their inhibition potency (Ki, μmol/l) decreased in the order of fluoxetine (0.411)>norfluoxetine (1.38)>fluvoxamine (10.1)>citalopram (10.9). Liver microsomes prepared fromCYP2D6-transgenic mice showed about 16-fold higher 5-MTO-demethylase activity than that from wild-type mice. After the intravenous co-administration of 5-MT (10 mg/kg) and pargyline (20 mg/kg), serum 5-HT level was about 3-fold higher inCYP2D6-transgenic mice than wild-type mice. When dosed with α,α,β,β-d4-5-MT, α,α,β,β-d4-5-HT was detected inCYP2D6transgenic mouse serum, and its content was much higher than wild-type mouse. α,α,β,β-d4-5-HT was not produced inCYP2D6-transgenic mice pretreated with quinidine. The regeneration of 5-HT from 5-MT provides the missing link in the serotonin–melatonin cycle. Up to 10% of the population lacks this enzyme. It is proposed that this common inborn error in 5-MTO-demethylation to serotonin influences a range of neurophysiologic and pathophysiologic events.

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:2003

数据来源: OVID