Modulation of aldosterone biosynthesis by adrenodoxin mutants with different electron transport efficiencies.
(49/2276)
Aldosterone biosynthesis is highly regulated on different levels by hormones, potassium, lipid composition of the membrane and the molecular structure of its gene. Here, the influence of the electron transport efficiency from adrenodoxin (Adx) to CYP11B1 on the activities of bovine CYP11B1 has been investigated using a liposomal reconstitution system with truncated mutants of Adx. It could be clearly demonstrated that Adx mutants Adx 4-114 and Adx 4-108, possessing enhanced electron transfer abilities, produce increases in corticosterone and aldosterone biosynthesis. Based on the Vmax values of corticosterone and aldosterone formation, Adx 4-108 and Adx 4-114 enhance corticosterone synthesis 1.3-fold and aldosterone formation threefold and twofold, respectively. The production of 18-hydroxycorticosterone was changed only slightly in these Adx mutants. The effect of Adx 1-108 on the product patterns of bovine CYP11B1, human CYP11B1 and human CYP11B2 was confirmed in COS-1 cells by cotransfection of CYP11B- and Adx-containing expression vectors. It could be shown that Adx 1-108 enhances the formation of aldosterone by bovine CYP11B1 and by human CYP11B2, and stimulates the production of corticosterone by bovine CYP11B1 and human CYP11B1 and CYP11B2 also. (+info)
Overhydroxylation of lysyl residues is the initial step for altered collagen cross-links and fibril architecture in fibrotic skin.
(50/2276)
In fibrotic skin of lipodermatosclerosis a substantial increase of the cross-link hydroxylysylpyridinoline is observed. Hydroxylysylpyridinoline is a typical cross-link of skeletal tissue and is thought to play a major part in the hardening of sclerotic tissue. We investigated whether the increase in hydroxylysylpyridinoline is due to overhydroxylation of lysyl residues in the collagen molecule, which may also be associated with an increase of glycosylated hydroxylysine residues. Furthermore, we determined whether the collagen fibrils in lipodermatosclerosis showed a decrease of the diameter in the tissue as well as in vitro after fibrillogenesis of pepsin-solubilized collagens. Isolated alpha-chains of pepsin solubilized collagen I showed an increase in lysyl hydroxylation (hyl/(hyl + lys)) as compared with normal control [alpha1(I): lipodermatosclerosis 0.18 +/- 0.01; control 0.12 +/- 0.01; alpha2(I): lipodermatosclerosis 0.36 +/- 0.02; control 0. 25 +/- 0.03, p < 0.001]. Furthermore, the content of enzymatic glycosylated hydroxlysine residues increased. This increase is associated with a decrease of fibril diameter of both tissue and fibrils formed in vitro of pepsin-solubilized collagens. In the same pool of collagens an increase in collagen III content was observed as compared with controls (lipodermatosclerosis 14.5% +/- 1.6, control 10.3% +/- 1.6, p < 0.001). Our results showed that the overhydroxylation of lysyl residues, which is required for the generation of hydroxylysylpyridinoline, is not only restricted to the telopeptides but also affects the helical part of the molecule. This process is further associated with an increase of glycosylated hydroxylysyl residues. These changes along with the increase in collagen III content seem to be responsible for the observed alteration in the architecture of collagen fibrils in sclerotic skin. (+info)
N-demethylation accompanies alpha-hydroxylation in the metabolic activation of tamoxifen in rat liver cells.
(51/2276)
Previous work has shown that a major route of activation of tamoxifen to DNA-binding products in rat liver cells is via alpha-hydroxylation leading to modification of the N(2)-position of guanine in DNA and to a lesser extent the N(6)-position of adenine. Improved resolution by HPLC has now identified two major adducts in rat liver DNA, one of them the aforementioned tamoxifen-N(2)-guanine adduct and the other the equivalent adduct in which the tamoxifen moiety has lost a methyl group. Treatment of rats or rat hepatocytes with N-desmethyltamoxifen gave rise to the second adduct, whereas treatment with tamoxifen or alpha-hydroxytamoxifen gave rise to both. Furthermore, N,N-didesmethyltamoxifen was found to be responsible for an additional minor DNA adduct formed by tamoxifen, alpha-hydroxytamoxifen and N-desmethyltamoxifen. The involvement of metabolism at the alpha position was confirmed in experiments in which [alpha-D(2)-ethyl]tamoxifen, but not [beta-D(3)-ethyl]tamoxifen, produced reduced levels of DNA adducts. Tamoxifen N-oxide and alpha-hydroxytamoxifen N-oxide also gave rise to DNA adducts in rat liver cells, but the adduct patterns were very similar to those formed by tamoxifen and alpha-hydroxytamoxifen, indicating that the N-oxygen is lost prior to DNA binding. These and earlier results demonstrate that in rat liver cells in vivo and in vitro, Phase I metabolic activation of tamoxifen involves both alpha-hydroxylation and N-demethylation, which is followed by Phase II activation at the alpha-position to form a highly reactive sulphate. Detection of tamoxifen-related DNA adducts by (32)P-postlabelling is achieved with >90% labelling efficiency. (+info)
A high-throughput digital imaging screen for the discovery and directed evolution of oxygenases.
(52/2276)
BACKGROUND: Oxygenases catalyze the hydroxylation of a wide variety of organic substrates. An ability to alter oxygenase substrate specificities and improve their activities and stabilities using recombinant DNA techniques would expand their use in processes such as chemical synthesis and bioremediation. Discovery and directed evolution of oxygenases require efficient screens that are sensitive to the activities of interest and can be applied to large numbers of crude enzyme samples. RESULTS: Horseradish peroxidase (HRP) couples the phenolic products of hydroxylation of aromatic substrates to generate colored and/or fluorescent compounds that are easily detected spectroscopically in high-throughput screening. Coexpression of the coupling enzyme with a functional mono- or dioxygenase creates a pathway for the conversion of aromatic substrates into fluorescent compounds in vivo. We used this approach for detecting the products of the toluene-dioxygenase-catalyzed hydroxylation of chlorobenzene and to screen large mutant libraries of Pseudomonas putida cytochrome P450cam by fluorescence digital imaging. Colors generated by the HRP coupling reaction are sensitive to the site of oxygenase-catalyzed hydroxylation, allowing the screen to be used to identify catalysts with new or altered regiospecificities. CONCLUSIONS: The coupled oxygenase-peroxidase reaction system is well suited for screening oxygenase libraries to identify mutants with desired features, including higher activity or stability and altered reaction specificity. This approach should also be useful for screening expressed DNA libraries and combinatorial chemical libraries for hydroxylation catalysts and for optimizing oxygenase reaction conditions. (+info)
The power of evolution: accessing the synthetic potential of P450s.
(53/2276)
Cytochromes P450 can catalyse hydroxylation reactions that are of considerable potential synthetic value, but a number of practical difficulties have hitherto prevented their use for this purpose. Recent advances, including intelligently designed laboratory evolution experiments, promise to overcome these obstacles, and to add P450s to the enzymatic armoury of the chemist. (+info)
Failure to respond to treatment with typical antipsychotics is not associated with CYP2D6 ultrarapid hydroxylation.
(54/2276)
AIMS: To investigate whether or not there is a correlation between failure to respond to typical antipsychotics and CYP2D6 ultrarapid metaboliser status. METHODS: CYP2D6 phenotype (metaboliser status) was assigned following genotyping for gene duplication, as well as for the CYP2D6*3, CYP2D6*4, and CYP2D6*5 null alleles in 235 treatment-refractory patients and 73 nonrefractory patients. RESULTS: Four (1.7%) of the 235 treatment-refractory subjects were positive on the duplication assay, but, of these, two were found to represent duplications of a null allele (CYP2D6*4 ), therefore leaving only two (0.85%) positive for duplication of a wild type allele (ultrarapid metabolisers). Three (4.1%) of the nonrefractory subjects had a genotype consistent with ultrarapid metaboliser status. Fisher's exact test gave a two-tailed P value of 0.091, i.e. a trend towards an excess of ultrarapid metabolisers in the nonrefractory group, which was in the opposite direction to that predicted by our hypothesis. CONCLUSIONS: Although the results show a trend towards an excess of ultrarapid metabolisers in the nonrefractory group, the percentages in the two groups of patients are both within the range for ultrarapid metabolisers in Caucasian populations. Our data are not consistent with ultrarapid metaboliser status being a major cause of failure to respond to typical antipsychotics. (+info)
Genetic polymorphism of (S)-mephenytoin 4'-hydroxylation in populations of African descent.
(55/2276)
AIMS: The frequency of CYP2C19 poor metabolizers (PMs) in populations of African descent has been reported to range from 1.0% to 35.4%. In order to determine with greater certainty the frequency of CYP2C19 PMs in such black populations we have performed a meta-analysis of the studies. METHODS: Relevant data on the frequency of both the PM phenotype of probe drugs (mephenytoin, omeprazole, and proguanil), and the distribution frequencies of CYP2C19 alleles and genotypes in black populations were summarized and reanalysed using a meta-analytical approach. RESULTS: Of nine reported studies two were excluded because of significant heterogeneity (chi2=115, P<0.0001). The combined data from the remaining seven studies showed that the frequency of the PM phenotype in 922 healthy unrelated black Africans and black Americans ranged from 1.0% to 7.5% (n=7 for combined data) with an overall frequency being 3.9% (36 of 922; 95%CI: 2.7%-5.2%). The frequency of the PM genotypes in blacks was 3.7% (36 of 966; 95%CI: 2.5%-4.9%), in agreement with the frequency of the PM phenotype. In the extensive metabolizers (EMs) 29% (271 of 930) were heterozygotes (wt/m ). The observed frequencies of the three Mendelian genotypes were 0.68 for wt/wt, 0.28 for wt/m, and 0.04 for m/m. The allelic distribution was appropriate at 82.3% (95%CI: 80.5%-83.9%) for CYP2C19*1, 17.3% (95%CI:15.7%-19.0%) for CYP2C19*2 (m1 ), and 0.4% (95%CI: 0.1%-0.7%) for CYP2C19*3 (m2 ) in these populations. CONCLUSIONS: We conclude that subjects of African ancestry have a low frequency of the CYP2C19 PM phenotype and genotype; that the defective CYP2C19 alleles are uncommon, and that a small proportion of heterozygotes exists in the EM subpopulation. (+info)
DNA cleavage by hydroxy-salicylidene-ethylendiamine-iron complexes.
(56/2276)
Bis(hydroxy)salen.Fe complexes were designed as self-activated chemical nucleases. The presence of a hy-droxyl group on the two salicylidene moieties serve to form a hydroquinone system cooperating with the iron redox system to facilitate spontaneous formation of free radicals. We compared the DNA binding and cleaving properties of the ortho -, meta- and para -(bishydroxy) salen.Fe complexes with that of the corresponding chelate lacking the hydroxyl groups. DNA melting temperature studies indicated that the para complex exhibits the highest affinity for DNA. In addition, this para compound was considerably more potent at cleaving supercoiled plasmid DNA than the regio-isomeric ortho - and meta -hydroxy-salen.Fe complexes, even in the absence of a reducing agent, such as dithiothreitol used to activate the metal complex. The DNA cleaving activity of the para isomer is both time and concentration dependent and the complexed iron atom is absolutely essential for the sequence uniform cleavage of DNA. From a mechanistic point of view, electron spin resonance measurements suggest that DNA contributes positively to the activation of the semi-quinone system and the production of ligand radical species responsible for subsequent strand scission in the absence of a reducing agent. The para -hydroxy-salen.Fe complex has been used for detecting sequence-specific drug-DNA interactions. Specific binding of Hoechst 33258 to AT sequences and chromomycin to GC sequences were shown. The para -bis(hydroxy)salen.Fe derivative complements the tool box of footprinting reagents which can be utilised to produce efficient cleavage of DNA. (+info)