Biomedical subjects

D Li

Publications and source records attributed to D Li.

At least 91 records · Page 5Linked to original sources

PubMed2001

KLF6, a candidate tumor suppressor gene mutated in prostate cancer.

Kruppel-like factor 6 (KLF6) is a zinc finger transcription factor of unknown function. Here, we show that the KLF6 gene is mutated in a subset of human prostate cancer. Loss-of-heterozygosity analysis revealed that one KLF6 allele is deleted in 77% (17 of 22) of primary prostate tumors. Sequence analysis of the retained KLF6 allele revealed mutations in 71% of these tumors. Functional studies confirm that whereas wild-type KLF6 up-regulates p21 (WAF1/CIP1) in a p53-independent manner and significantly reduces cell proliferation, tumor-derived KLF6 mutants do not. Our data suggest that KLF6 is a tumor suppressor gene involved in human prostate cancer.

Alleles↗

PubMed2001

Transforming growth factor-beta(1) modulates oxidatively modified LDL-induced expression of adhesion molecules: role of LOX-1.

Oxidatively modified LDL (ox-LDL) activates a lectin-like receptor, LOX-1, which results in the expression of adhesion molecules on endothelial surface. We investigated the regulation of the expression of transforming growth factor-beta(1) (TGF-beta(1)) and its receptors by ox-LDL and the functional significance of this interaction with regard to adhesion molecule expression in human coronary artery endothelial cells (HCAECs). Ox-LDL, in a time- and concentration-dependent manner, upregulated the expression of all 3 subtypes (1, 2, and 3 [including endoglin]) of TGF-beta(1) receptors and decreased active TGF-beta(1) synthesis (all P<0.05 versus control and native-LDL-treated cells). Treatment of HCAECs with a monoclonal antibody to LOX-1 attenuated ox-LDL-mediated upregulation of TGF-beta(1) receptors and decrease in TGF-beta(1) synthesis (P<0.05 versus ox-LDL alone). Ox-LDL also enhanced the expression of P-selectin and ICAM-1 as well as monocyte adhesion to HCAECs (P<0.05 versus control untreated cells). Pretreatment with recombinant TGF-beta(1) attenuated the enhanced expression of adhesion molecules and monocyte adhesion to HCAECs (P<0.05 versus ox-LDL alone). Effects of recombinant TGF-beta(1) were blocked by antibody to TGF-beta(1) receptor type 2, but not by antibody to endoglin. Thus ox-LDL, via activation of LOX-1, increases the expression of TGF-beta(1) receptors and decreases TGF-beta(1) synthesis in HCAECs. Recombinant TGF-beta(1), by binding to TGF-beta(1) type 2 receptors, modulates ox-LDL-mediated expression of adhesion molecules and monocyte adhesion to HCAECs.

Antibodies↗

PubMed2001

A tumor host range selection procedure identifies p150(sal2) as a target of polyoma virus large T antigen.

Cancer cells may undergo loss or alterations in functions that certain viruses normally target to promote virus replication. Virus mutants that have lost the targeting function(s) should be able to grow in such cancer cells but not in normal cells. A "tumor host range" (t-hr) selection procedure has been devised and applied to polyoma virus based on this rationale. Studies of one t-hr mutant have led to the identification of the mSal2 gene product (p150(sal2)) as a binding partner of the large T antigen. mSal2 encodes a multizinc finger protein and putative transcription factor homologous to the Drosophila homeotic gene Spalt. The t-hr mutant encodes an altered large T protein that fails to interact with p150(sal2) and is defective in replication and tumor induction in newborn mice.

3T3 Cells↗

PubMed2001

Sensitivity to benzo(a)pyrene diol-epoxide associated with risk of breast cancer in young women and modulation by glutathione S-transferase polymorphisms: a case-control study.

Mounting epidemiological evidence suggests that smoking may play a role in the etiology of breast cancer. Because smoking-related DNA adducts are detectable in both normal and malignant breast tissues, we hypothesized that breast cancer patients may be sensitive to tobacco-induced carcinogenesis, and this sensitivity could be modulated by variants of metabolic genes. To test this hypothesis, we evaluated benzo(a)pyrene diol-epoxide (BPDE)-induced mutagen sensitivity and polymorphisms of GSTM1 and GSTT1 in a pilot case-control study of breast cancer. Short-term cell cultures were established from blood samples of 100 female breast cancer patients and 105 healthy controls. After 5 h of in vitro exposure to 4 microM of BPDE, we harvested the lymphocytes for cytogenetic evaluation and recorded and compared the frequency of BPDE-induced chromatid breaks between cases and controls. We used a multiplex PCR-based assay to simultaneously detect polymorphisms of GSTM1 and GSTT1 from genomic DNA. We performed univariate and multivariate logistic regression analyses and calculated odds ratios (OR) and 95% confidence intervals (CIs). Cases had a significantly higher frequency of chromatid breaks than did controls (P < 0.0001). The level of chromatid breaks greater than the median value of controls was associated with a >3-fold increased risk of breast cancer [adjusted odds ratio (ORadj) = 3.11; 95% CI = 1.72-5.64]. The risk was more pronounced in those who were < 45 years (ORadj = 4.79; 95% CI = 1.87-12.3), ever-smokers (ORadj = 5.55; 95% CI = 1.85-16.6), alcohol drinkers (ORadj = 4.64; 95% CI = 1.70-12.7), and those who had the GSTT1 null variant (ORadj = 8.01; 95% CI = 1.16-55.3). These data suggest that sensitivity to BPDE-induced chromosomal aberrations may contribute to the risk of developing breast cancer, and such sensitivity may be modulated by both genetic and environmental factors. Larger studies are needed to confirm our findings.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed2001

Effects of angiotensin-converting enzyme inhibition on the development of the atrial fibrillation substrate in dogs with ventricular tachypacing-induced congestive heart failure.

BACKGROUND: Atrial structural remodeling creates a substrate for atrial fibrillation (AF), but the underlying signal transduction mechanisms are unknown. This study assessed the effects of ACE inhibition on arrhythmogenic atrial remodeling and associated mitogen-activated protein kinase (MAPK) changes in a dog model of congestive heart failure (CHF). METHODS AND RESULTS: Dogs were subjected to various durations of ventricular tachypacing (VTP, 220 to 240 bpm) in the presence or absence of oral enalapril 2 mg. kg(-1). d(-1). VTP for 5 weeks induced CHF, local atrial conduction slowing, and interstitial fibrosis and prolonged atrial burst pacing-induced AF. Atrial angiotensin II concentrations and MAPK expression were increased by tachypacing, with substantial changes in phosphorylated forms of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38-kinase. Enalapril significantly reduced tachypacing-induced changes in atrial angiotensin II concentrations and ERK expression. Enalapril also attenuated the effects of CHF on atrial conduction (conduction heterogeneity index reduced from 3.1+/-0.4 to 1.9+/-0.2 ms/mm, P<0.05), atrial fibrosis (from 11.9+/-1.1% to 7.5+/-0.4%, P<0.01), and mean AF duration (from 651+/-164 to 218+/-75 seconds, P<0.05). Vasodilator therapy of a separate group of VTP dogs with hydralazine and isosorbide mononitrate did not alter CHF-induced fibrosis or AF promotion. CONCLUSIONS: CHF-induced increases in angiotensin II content and MAPK activation contribute to arrhythmogenic atrial structural remodeling. ACE inhibition interferes with signal transduction leading to the AF substrate in CHF and may represent a useful new component to AF therapy.

Angiotensin II↗

PubMed2001

Generation of three selenium-containing catalytic antibodies with high catalytic efficiency using a novel hapten design method.

A novel strategy for design of haptens that were used to produce catalytic antibodies was developed and three monoclonal antibodies, 3G5, 2F3, and 5C9, were generated using this strategy. These monoclonal antibodies were converted into selenium-containing abzymes by chemically modifying the hydroxyl group of serines followed by sodium hydrogen selenide displacement. These selenium-containing abzymes exhibited remarkable glutathione peroxidase activity, which surpasses the activity of some native glutathione peroxidases. The activities of the selenium-containing abzymes Se-3G5, Se-2F3, and Se-5C9 which catalyzed reduction of hydroperoxides by glutathione were 2.23, 4.20, and 3.79 times that of rabbit liver glutathione peroxidase, respectively. Detailed steady-state kinetics study on Se-2F3 was carried out and the value of k(cat)/K(m) (H(2)O(2)) was found to be 2.11 x 10(7) M(-1) min(-1) which was supposed to be one of the highest among the known catalytic antibodies. The data of association constants and glutathione peroxidase activities of these catalytic antibodies and the steady-state kinetics of Se-2F3 showed that the method might be a remarkably efficient one for generating catalytic antibodies with glutathione peroxidase activity.

Amino Acid Sequence↗

PubMed2001

Novel cardiac troponin T mutation as a cause of familial dilated cardiomyopathy.

BACKGROUND: Familial dilated cardiomyopathy (FDCM) and hypertrophic cardiomyopathy (FHCM) are the 2 most common forms of primary cardiac muscle diseases. Studies indicate that mutations in sarcomeric proteins are responsible for FHCM and suggest that mutations in cytoskeletal proteins cause FDCM. Evidence is evolving, however, that such conclusions are premature. METHODS AND RESULTS: A novel missense mutation in the cardiac troponin T gene was identified by direct sequencing and confirmed by endonuclease restriction analysis in a large family with FDCM that we had previously mapped to chromosome 1q32. The mutation substitutes tryptophan for a highly conserved amino acid, arginine, at amino acid residue 141 (Arg141Trp). The mutation occurs within the tropomyosin-binding domain of cardiac troponin T and alters the charge of the residue. This mutation cosegregates with the disease, being present in all 14 living affected individuals. The mutation was not found in 100 normal control subjects. Clinical features were congestive heart failure with premature deaths. The age of onset and severity of the disease are highly variable, with incomplete penetrance. Because 15 mutations in troponin T are known to cause FHCM, 219 probands with FHCM were screened, and none had the mutation. CONCLUSIONS: Thus, the novel cardiac troponin T mutation Arg141Trp is responsible for FDCM in our family. Because several mutations in troponin T have already been recognized to be responsible for FHCM, it appears that the phenotype, whether it be hypertrophy or dilatation, is determined by the specific mutation rather than the gene.

Adult↗

PubMed2001

Mutational analysis of the membrane proximal heptad repeat of the newcastle disease virus fusion protein.

Paramyxovirus fusion proteins have two heptad repeat domains, HR1 and HR2, that have been implicated in the fusion activity of the protein. Peptides from these two domains form a six-stranded, coiled-coil with the HR1 sequences forming a central trimer and three molecules of the HR2 helix located within the grooves in the central trimer (Baker et al., 1999, Mol. Cell 3, 309; Zhao et al. 2000, Proc. Natl. Acad. Sci. USA 97, 14172). Nonconservative mutations were made in the HR2 domain of the Newcastle disease virus fusion protein in residues that are likely to form contacts with the HR1 core trimer. These residues form the hydrophobic face of the helix and adjacent residues ("a" and "g" positions in the HR2 helical wheel structure). Mutant proteins were characterized for effects on synthesis, steady-state levels, proteolytic cleavage, and surface expression as well as fusion activity as measured by syncytia formation, content mixing, and lipid mixing. While all mutant proteins were transport competent and proteolytically cleaved, these mutations did variously affect fusion activity of the protein. Nonconservative mutations in the "g" position had no effect on fusion. In contrast, single changes in the middle "a" position of HR2 inhibited lipid mixing, content mixing, and syncytia formation. A single mutation in the more carboxyl-terminal "a" position had minimal effects on lipid mixing but did inhibit content mixing and syncytia formation. These results are consistent with the idea that the HR2 domain is involved in posttranslational interactions with HR1 that mediate the close approach of membranes. These results also suggest that the HR2 domain, particularly the carboxyl-terminal region, plays an additional role in fusion, a role related to content mixing and syncytia formation.

Amino Acid Sequence↗

PubMed2001

Ionic remodeling of cardiac Purkinje cells by congestive heart failure.

BACKGROUND: Cardiac Purkinje cells (PCs) are important for the generation of triggered arrhythmias, particularly in association with abnormal repolarization. The effects of congestive heart failure (CHF) on the ionic properties of PCs are unknown. METHODS AND RESULTS: PCs were isolated from false tendons of control dogs and dogs with ventricular tachypacing-induced CHF. CHF PCs were hypertrophied (capacitance, mean+/-SEM, 149+/-4 pF, n=130; versus 128+/-3 pF, n=150, control; P<0.001). Transient outward current density was reduced in CHF PCs without change in voltage dependence or kinetics. CHF also reduced inward-rectifier current density, with no change in form of the current-voltage relationship. Densities of L- and T-type calcium, rapid and slow delayed rectifier, and Na(+)-Ca(2+) exchange currents were unaltered by CHF, but L-type calcium current inactivation was slowed at positive potentials. Purkinje fiber action potentials from CHF dogs showed decreased phase 1 amplitudes and elevated plateau voltages and demonstrated twice as much prolongation on exposure to the rapid delayed rectifier blocker E-4031 as control Purkinje fibers. CONCLUSIONS: CHF causes remodeling of important K(+) and Ca(2+) currents in cardiac PCs, decreasing repolarization reserve and causing an exaggerated repolarization delay in response to a class III drug. These results have important potential implications regarding ventricular arrhythmogenesis, particularly related to triggered activity in PCs, in patients with CHF.

Action Potentials↗

PubMed2001

Studies on the inactivation of bovine liver enoyl-CoA hydratase by (methylenecyclopropyl)formyl-CoA: elucidation of the inactivation mechanism and identification of cysteine-114 as the entrapped nucleophile.

The inhibitory properties of (methylenecyclopropyl)formyl-CoA (MCPF-CoA), a metabolite derived from a natural amino acid, (methylenecyclopropyl)glycine, against bovine liver enoyl-CoA hydratase (ECH) were characterized. We have previously demonstrated that MCPF-CoA specifically targets ECHs, which catalyze the reversible hydration of alpha,beta-unsaturated enoyl-CoA substrates to the corresponding beta-hydroxyacyl-CoA products. Here, we synthesized (R)- and (S)-diastereomers of MCPF-CoA to examine the stereoselectivity of this inactivation. Both compounds were shown to be competent inhibitors for bovine liver ECH with nearly identical second-order inactivation rate constants (k(inact)/K(I)) and partition ratios (k(cat)/k(inact)), indicating that the inactivation is nonstereospecific with respect to ring cleavage. The inhibitor, upon incubation with bovine liver ECH, labels a tryptic peptide, ALGGGXEL, near the active site of the protein, where X is the amino acid that is covalently modified. Cloning and sequence analysis of bovine liver ECH gene revealed the identity of the amino acid residue entrapped by MCPF-CoA as Cys-114 (mature sequence numbering). On the basis of gHMQC (gradient heteronuclear multiple quantum coherence) analysis with [3-(13)C]-labeled MCPF-CoA, the ring cleavage is most likely induced by the nucleophilic attack at the terminal carbon of the exomethylene group (C(2)'). We propose a plausible inactivation mechanism that involves relief of ring strain and is consistent with examples found in the literature. In addition, these studies provide important clues for future design of more efficient and selective inhibitors to control and/or regulate fatty acid metabolism.

Acyl Coenzyme A↗

PubMed2001

Magnetic resonance imaging permits in vivo monitoring of catheter-based vascular gene delivery.

BACKGROUND: Gene therapy is an exciting frontier in modern medicine. To date, most investigations about the imaging of gene therapy have primarily focused on noncardiovascular systems, and no in vivo imaging modalities are currently available for monitoring vascular gene therapy. The purpose of this study was to develop an in vivo imaging tool to monitor a catheter-based vascular gene delivery procedure. METHODS AND RESULTS: We produced gadolinium/blue dye and gadolinium/gene-vector media by mixing Magnevist with a trypan-blue or a lentiviral vector carrying a green fluorescent protein (GFP) gene. The gadolinium was used as an imaging marker for magnetic resonance (MR) imaging to visualize vessel wall enhancement, and the blue dye/GFP was used as a tissue stain marker for histology/immunohistochemistry to confirm the success of the transfer. Using Remedy gene delivery catheters, we transferred the gadolinium/blue dye (n=8) or gadolinium/GFP lentivirus (n=4) into the arteries of 12 pigs, that were monitored under high-resolution MR imaging. The results showed, in all 12 pigs, the gadolinium enhancement of the target vessel walls on MR imaging and the blue/GFP staining of the target vessel tissues with histology/immunohistochemistry. This study shows the potential of using MR imaging to dynamically visualize (1) where the gadolinium/genes are delivered; (2) how the target portion is marked; and (3) whether the gene transfer procedure causes complications. CONCLUSIONS: We present a technical development that uses high-resolution MR imaging as an in vivo imaging tool to monitor catheter-based vascular gene delivery.

Animals↗

PubMed2001

Cloning and characterization of two promoters for the human HSAL2 gene and their transcriptional repression by the Wilms tumor suppressor gene product.

HSAL2 is a member of a gene family that encodes a group of putative developmental transcription factors. The HSAL gene complex was originally identified on the basis of DNA sequence homology to a region-specific homeotic gene (SAL) in Drosophila. This study reveals a novel, functional 5' exon for HSAL2 and demonstrates that two distinct HSAL2 gene transcripts arise from two overlapping transcription units, resulting in proteins that differ by 25 amino acids. By utilizing functional luciferase reporter assays, two distinct promoters for HSAL2, P1 for the proximal promoter (upstream of exon 1) and P2 for the distal promoter (upstream of exon 1A), were identified. Evaluation of mRNA prevalence and tissue specificity, with particular focus on adult tissues, revealed that production of mRNA from P1 was selective and relatively rare. Production of mRNA from P2 was demonstrably higher and was expressed by a greater number of tissues. In contradistinction, HSAL2 expression directed by P2 was undetectable in some malignant populations as opposed to their normal human counterparts, suggesting a potential role as a tumor suppressor gene. Consensus-binding sites were identified for several transcriptional factors, with multiple sites for WT-1, and Hox-1.3 present within both the P1 and P2 regions. In transient transfection assays, transcription from both HSAL2 P1 and P2 was strikingly repressed by the WT-1 tumor suppressor protein. These findings suggest that an intracellular WT-1/HSAL2 pathway may play a role in development and hematopoiesis.

Amino Acid Sequence↗

PubMed2001

Insulin accelerates inter-endosomal GLUT4 traffic via phosphatidylinositol 3-kinase and protein kinase B.

Insulin enhances plasmalemmal-directed traffic of glucose transporter-4 (GLUT4), but it is unknown whether insulin regulates GLUT4 traffic through endosomal compartments. In L6 myoblasts expressing Myc-tagged GLUT4, insulin markedly stimulated the rate of GLUT4myc recycling. In myoblasts stimulated with insulin to maximize surface GLUT4myc levels, we followed the rates of surface-labeled GLUT4myc endocytosis and chased its intracellular distribution in space and time using confocal immunofluorescence microscopy. Surface-labeled GLUT4myc internalized rapidly (t(12) 3 min), reaching the early endosome by 2 min and the transferrin receptor-rich, perinuclear recycling endosome by 20 min. Upon re-addition of insulin, the t(12) of GLUT4 disappearance from the plasma membrane was unchanged (3 min), but strikingly, GLUT4myc reached the recycling endosome by 10 and left by 20 min. This effect of insulin was blocked by the phosphatidylinositol 3-kinase inhibitor LY294002 or by transiently transfected dominant-negative phosphatidylinositol 3-kinase and protein kinase B mutants. In contrast, insulin did not alter the rate of arrival of rhodamine-labeled transferrin at the recycling endosome. These results reveal a heretofore unknown effect of insulin to accelerate inter-endosomal travel rates of GLUT4 and identify the recycling endosome as an obligatory stage in insulin-dependent GLUT4 recycling.

Animals↗

PubMed2001

Rays and arrays: the transcriptional program in the response of human epidermal keratinocytes to UVB illumination.

The epidermis, our first line of defense from ultraviolet (UV) light, bears the majority of photodamage, which results in skin thinning, wrinkling, keratosis, and malignancy. Hypothesizing that skin has specific mechanisms to protect itself and the organism from UV damage, we used DNA arrays to follow UV-caused gene expression changes in epidermal keratinocytes. Of the 6,800 genes examined, UV regulates the expression of at least 198. Three waves of changes in gene expression can be distinguished, 0.5-2, 4-8, and 16-24 h after illumination. The first contains transcription factors, signal transducing, and cytoskeletal proteins that change cell phenotype from a normal, fast-growing cell to an activated, paused cell. The second contains secreted growth factors, cytokines, and chemokines; keratinocytes, having changed their own physiology, alert the surrounding tissues to the UV damage. The third wave contains components of the cornified envelope, as keratinocytes enhance the epidermal protective covering and, simultaneously, terminally differentiate and die, removing a carcinogenic threat. UV also induces the expression of mitochondrial proteins that provide additional energy, and the enzymes that synthesize raw materials for DNA repair. Using a novel skin organ culture model, we demonstrated that the UV-induced changes detected in keratinocyte cultures also occur in human epidermis in vivo.

Chemokines↗

PubMed2001

The low density lipoprotein receptor-related protein/alpha2-macroglobulin receptor is a receptor for connective tissue growth factor.

Connective tissue growth factor (CTGF) expression is regulated by transforming growth factor-beta (TGF-beta) and strong up-regulation occurs during wound healing; in situ hybridization data indicate that there are high levels of CTGF expression in fibrotic lesions. Recently the binding parameters of CTGF to both high and lower affinity cell surface binding components have been characterized. Affinity cross-linking and SDS-polyacrylamide gel electrophoresis analysis demonstrated the binding of CTGF to a cell surface protein with a mass of approximately 620 kDa. We report here the purification of this protein by affinity chromatography on CTGF coupled to Sepharose and sequence information obtained by mass spectroscopy. The binding protein was identified as the multiligand receptor, low density lipoprotein receptor-related protein/alpha2-macroglobulin receptor (LRP). The identification of LRP as a receptor for CTGF was validated by several studies: 1) binding competition with many ligands that bind to LRP, including receptor-associated protein; 2) immunoprecipitation of CTGF-receptor complex with LRP antibodies; and 3) cells that are genetically deficient for LRP were unable to bind CTGF. Last, CTGF is rapidly internalized and degraded and this process is LRP-dependent. In summary, our data indicate that LRP is a receptor for CTGF, and may play an important role in mediating CTGF biology.

Amino Acid Sequence↗

PubMed2001

Stabilimenta attract unwelcome predators to orb-webs.

Conspicuous behaviour exposes animals to predation; prey-attraction thus often conflicts with antipredator behaviour. The fact that a conspicuous ultraviolet-light reflecting silken structure in the orb-webs of certain spider species, known as a stabilimentum, makes the webs obvious to both prey and predators has been used to argue that spiders benefit from building stabilimenta by attracting prey and/or defending against visually hunting predators. Here, we provide experimental evidence that stabilimenta can act as visual signals that attract web-invading spider-eating predators with acute vision to the webs. We also show that the predators can learn to remember a particular type of stabilimentum. Thus, stabilimentum-building spiders risk a high level of predation by attracting visually hunting predators.

Animals↗

PubMed2001

In vitro BPDE-induced DNA adducts in peripheral lymphocytes as a risk factor for squamous cell carcinoma of the head and neck.

The level of DNA adducts under the same conditions of carcinogen exposure and cell proliferation reflects an integrated measure of carcinogen metabolism and DNA repair. Therefore, such DNA adduct levels have the potential to be a biomarker for susceptibility to chemical carcinogenesis. In a pilot study of 91 patients with squamous cell carcinomas of the head and neck and 115 controls who were frequency matched by age, sex, ethnicity, and smoking status, we applied a newly developed in vitro assay of benzo[a]pyrene diol epoxide (BPDE)-induced DNA adducts in short-term peripheral lymphocytes cultures. Levels of BPDE-DNA adducts were found to be significantly higher in cases than in controls (mean +/- SD, 76.8 +/- 77.4/10(7) and 47.1 +/- 48.0/10(7) nucleotides, respectively; p < 0.001). Using the median level of control values (35/10(7)) as the cut-off point, about 66% of cases were distributed above this level. Logistic regression analysis revealed that the level of BPDE-induced DNA adducts was an independent risk factor (odds ratio = 2.22; 95% confidence interval = 1.22--4.04) after adjustment for age, sex and smoking status. Further stratified analyses showed that levels of the induced adducts between cases and controls were significantly higher in both age groups, that is, younger or older than 60, as well as in both men and women. Smoking had a positive effect on the induced adducts. The highest level of induced adducts was seen in current smokers, then former smokers and non-smokers. There was a statistically significant dose--response relationship between the quartile levels of BPDE-induced DNA adducts and the risk of head and neck cancer (trend test, p = 0.003). Despite the relatively small sample size, the association of BPDE-induced DNA adducts and cancer risk suggests that this assay has the potential to complement with other biomarkers in identifying individuals at increased risk of developing tobacco-related cancers.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed2001

Crystal structure of precorrin-8x methyl mutase.

BACKGROUND: The crystal structure of precorrin-8x methyl mutase (CobH), an enzyme of the aerobic pathway to vitamin B12, provides evidence that the mechanism for methyl migration can plausibly be regarded as an allowed [1,5]-sigmatropic shift of a methyl group from C-11 to C-12 at the C ring of precorrin-8x to afford hydrogenobyrinic acid. RESULTS: The dimeric structure of CobH creates a set of shared active sites that readily discriminate between different tautomers of precorrin-8x and select a discrete tautomer for sigmatropic rearrangement. The active site contains a strictly conserved histidine residue close to the site of methyl migration in ring C of the substrate. CONCLUSION: Analysis of the structure with bound product suggests that the [1,5]-sigmatropic shift proceeds by protonation of the ring C nitrogen, leading to subsequent methyl migration.

Amino Acid Sequence↗