A mutated murine reduced folate carrier (RFC1) with increased affinity for folic acid, decreased affinity for methotrexate, and an obligatory anion requirement for transport function

In an ongoing study of structure-function relationships of the murine reduced folate carrier 1 (RFC1), a glutamate to lysine mutation at amino acid 45 was identified in a methotrexate (MTX)-resistant L1210 clonal variant in which MTX and 5-formyltetrahydrofolate (5-CHO-THF) influx was markedly decreased. The characteristics of the mutated carrier, RFC1-E45K, were studied by cDNA transfection into the murine MTXrA line in which endogenous carrier is not functional. Folic acid influx doubled in the transfectant MTXrA-E45K as compared with L1210 or MTXrA cells; in contrast, MTX and 5-CHO-THF influx was only 14 and 27% that of L1210 cells, respectively. 5-CHO-THF influx in MTXrA-E45K cells was characterized by a 12- and 3.6-fold decrease in influx Vmax and Kt respectively, relative to L1210 cells. The folic acid influx Ki in L1210 cells was more than 50-fold greater than that of MTX based upon inhibition of 5-CHO-THF influx. In comparison, the mutated carrier had comparable affinities for folic acid and MTX in MTXrA-E45K cells due to a 7-fold decrease in the folic acid influx Ki and 7-fold increase in the MTX influx Ki. Transport via native RFC1 is inhibited by a variety of anions in L1210 cells associated with an increase in influx Kt. However, influx of 5-CHO-THF in MTXrA-E45K cells in a HEPES buffer (9 mM chloride) was decreased by 70% due to a 3-fold fall in the Vmax. In the complete absence of chloride (K+-HEPES-sucrose buffer) 5-CHO-THF influx was only 10% that in HBS buffer. 5-CHO-THF influx was restored by addition of chloride, fluoride, or nitrate but not by sulfate, phosphate, or ATP which were all inhibitory over a broad range of concentrations. The data suggest that substitution of a positive for a negative amino acid at position 45 results in the loss of RFC1 mobility in the absence of small inorganic anions that bind to, and neutralize the positive charge on, the lysine residue. Inhibition by higher charged anions may be due to interactions at another carrier site present in both the mutated and wild type carrier. This and other studies suggest that amino acids in the first predicted transmembrane domain play an important role in determining the spectrum of affinities for, and mobility of, RFC1 and is a cluster region for mutations when cells are placed under selective pressure with antifolates that utilize RFC1 as the major route of entry into mammalian cells.

[The role of diet consultation on improvement of the diet nutrition in pregnant women]

OBJECTIVE

To study the improvement of the intakes of various nutrients including protein, fat, carbohydrate, fibers, calcium, iron, zinc et al, in pregnant women after appropriate diet consultation by doctors.

METHODS

100 cases of pregnant women coming to our diet consultation clinic were randomly selected, in which 50 cases (control group) came for the first time and another 50 cases (study group) were for the third visit at least. The diet nutrition of the study group after the second consultation were compared with that before consultation and with concurrent control group.

RESULTS

After diet consultation, except for retinol, the intake of various nutrients, including calorie intake, protein, fibers, magnesium, calcium, phosphorus, iron, zinc, vitamin E, riboflavin, thiamine, nicotinic acid, in study group were significantly improved compared with that of the study group before diet consultation and of the control group (P < 0.01).

CONCLUSION

Diet consultation plays excellent role in promoting scientific and appropriate nutrients intake of pregnant women.

[Relationship between lipometabolic disorder in stroke with TCM syndrome differentiation and typing]

OBJECTIVE

To analyse the relationship between lipometabolic disorder in stroke with TCM Syndrome Differentiation and Typing.

METHODS

The serum lipid, lipoprotein and apo-lipoprotein level of TCM treated group (142 cases) and control group (100 cases) were determined. The patients were subdivided into three Type-groups according to TCM Syndrome Differentiation: Phlegm-Dampness Stagnation (PDS), Yin Deficiency with Yang Hyperactivity (YDYH) and Qi Deficiency with Blood Stasis (QDBS) group.

RESULTS

The results showed that the level of TC, TG, HDL, LDL, apoA1, apoB and apoA1/apoB were significantly different in PDS and QDBS as compared with control group (P < 0.05, P < 0.01, respectively), while lipometabolic disorder of PDS was most serious in TCM Syndrome Differentiation of stroke. The level of TG, apoA1/apoB were significantly different in YDYH in comparing with control group (P < 0.05). While the level of TC, HDL, LDL and apoB were insignificantly different than those of control group (P > 0.05).

CONCLUSIONS

This study showed that lipometabolic disorder of stroke were correlated with Syndrome Differentiation of TCM. Stroke with PDS and QSBS should give removing Phlegm-Dampness, dredging Meridian and removing blood stasis treatment besides routine treatment.

Ginseng improves strategic learning by normal and brain-damaged rats

Adult rats were prepared with either sham or medial prefrontal cortex lesions and administered, beginning on the third post-operative day, either, 0, 40, or 80 mg kg-1 crude ginseng extract suspended in saline daily for the next 30 days. Later, kinetic functions were evaluated on an elevated rotating rod. No long-term influences of the treatments were observed on this task. Significant positive influences of ginseng were observed in the position reversal task. The learning deficits observed in the saline control brain-damaged rats were significantly attenuated in the ginseng-treated animals. An analysis of trial 2 response accuracy across reversals revealed enhanced cognitive abilities (i.e. acquisition of a win-stay, lose-shift strategy) in both the brain damaged and sham control rats administered ginseng. Generally, administration of the higher dose resulted in better performance in the learning paradigm. The exact mechanism responsible for these promising results remains to be discovered. Several possible mechanisms are discussed.

[Detection of hemophilia A carriers by PCR analysis of hind III polymorphism in the factor VIII gene]

OBJECTIVE

To explore a scheme of using PCR analysis in the detection of carriers of Hind III polymorphism of factor VIII gene of hemophilia A.

METHODS

Implicating intron 19 of the factor VIII gene of 6 patients with the hemophilia A and 207 unrelated X-chromosomes were amplified by PCR and were analysed by means of Amp-RFLPs of Hind III.

RESULTS

The incidence of the polymorphic Hind III sites in the given population was found to be 0.29. The frequence of the Hind III heterozygotes in women calculated according to Hardy-Weinberg equation was 0.41, which proved to be informative enough for carrier detection and prenatal diagnosis of hemophilia A. 2 out of 6 families (33%)examined in this study were informative.

CONCLUSION

The new scheme proved to be effective for hemophilia A carrier detection and prenatal diagnosis.

A reduced folate carrier mutation produces substrate-dependent alterations in carrier mobility in murine leukemia cells and methotrexate resistance with conservation of growth in 5-formyltetrahydrofolate

With 5-formyltetrahydrofolate (5-CHO-THF) as the folate source a methotrexate (MTX) transport-deficient murine leukemia cell line, L1210-G1a, was isolated after chemical mutagenesis and MTX selection. This cell line was 10-fold resistant to MTX in comparison to parental L1210 cells, yet the EC50 for 5-CHO-THF was increased by a factor of only 2. The initial uptake of MTX, at a concentration of 1 microM, was decreased by a factor of 40, whereas influx of 5-CHO-THF dropped by a factor of only 8. This difference in initial uptake rates was attributed solely to changes in influx Vmax without a significant change in Km. Whereas the RFC1 mRNA level in L1210-G1a cells was indistinguishable from that of parental L1210 cells, a serine to asparagine substitution was identified at amino acid 46 within the first predicted transmembrane domain. This was a result of a homozygous mutation of G-->A in the genome. Transfection of the mutated RFC1 cDNA into MTXrA cells, which lack functional endogenous carrier, resulted in a clonal derivative MTXrA-S46N. The increase in influx of 5-CHO-THF and 5-CH3THF was 5 and 13 times greater than that for MTX in the transfectant, consistent with the influx ratio in the L1210-G1a line. The functional expression of the mutated RFC1 reduced the growth requirement for 5-CHO-THF by a factor of 30, compared with only a 3-fold decrease in the MTX IC50. This represents the first reported RFC1 mutation that confers resistance to MTX due to a markedly impaired influx with relative conservation of reduced folate transport. The kinetic changes are consistent with a substrate-dependent alteration in carrier mobility that favors reduced folates over MTX. These changes may account for the development of MTX resistance due to impaired drug transport in vivo, allowing tumor cells to meet their folate requirement with 5-CH3THF, the predominant blood folate.

Synthesis, topoisomerase I inhibitory activity and in vitro cytotoxicity of camptothecin derivatives bearing five-membered heterocycle containing 10-substituents

A series of new camptothecin derivatives bearing certain five-membered heterocycles was synthesized and evaluated for in vitro cytotoxic activity. The cytotoxicity results show that camptothecin derivatives bearing pyrrole and thiophene rings were more potent than camptothecin, whereas those bearing furan were less active than camptothecin. Agarose gel electrophoresis shows different inhibitory activities of the camptothecin analogs towards topoisomerase I DNA cleavage. The pyrrole-containing compounds inhibit topoisomerase I DNA cleavage more strongly than camptothecin, but the thiophene and furan compounds do not show any inhibitory activities for DNA cleavage functions of topoisomerase I. Polyacrylamide gel sequencing electrophoresis shows that the pyrrole compounds induce single-strand breaks after incubating with a labeled DNA fragment. The results suggest that the pyrrole compounds fit the compound-enzyme-DNA complex better than camptothecin and the other analogs.

[Math-model of efficient cultivation of Angelica sinensis]

Using two-time general rotation-constitution design, the math-mdele has been founded about Angelica sinensis prodution efficiency and quantity of nitrogen, phosphorus and potassium to use by doing experiments in many different spots and production demonstration for testing and verifying. Accordin to the modle, computer is used to simulate the better, through which people can get fresh Chinese angelica over 500 Kg per mu and also net income over 500 yuan per mu. It shows that this is the best combination. 95% density riliability for this plan is 6860-7600 plants, pure nitrogen 18.75-22.2 Kg, P2O5 9.1-11.1 Kg and K2O 4.46-5.37 Kg One mu. Proportion for nitrogen, phosphorus, potassium is 1:0.49:0.24.

[The effects of Gu Chi Gao on IL-8 in GCF of periodontitis]

In order to find a new treatment of periodontitis, this paper studied the effects of Gu Chi Gao on IL-8 in gingival crevicular fluid (GCF) of periodontitis. One tooth was selected from every patient in 24 patients with adult periodontitis. After supragingival scaling, the patients were divided into two groups randomly. One group was treated with Gu Chi Gao, while the other group was untreated as control group. All patients were examined after one month. GCF samples were collected with 2 mm x 20 mm Whatman I filter paper stripes and IL-8 in the GCF samples were detected by the method of ELISA. The result demonstrated that the levels of GCF and IL-8 in the treated group were lower than that of control group (P < 0.01), it suggests that Gu Chi Gao may inhibit the production of IL-8 and GCF.

Impact of overexpression of the reduced folate carrier (RFC1), an anion exchanger, on concentrative transport in murine L1210 leukemia cells

Transport of reduced folates in murine leukemia cells is mediated by the bidirectional reduced folate carrier (RFC1) and independent unidirectional exit pumps. RFC1 has been proposed to be intrinsically equilibrating, generating transmembrane gradients by exchange with inorganic and organic anions. This paper defines the role of high level carrier expression, through transfection with RFC1 cDNA, on concentrative transport of the folate analog, methotrexate (MTX) in murine L1210 leukemia cells. RFC1 was expressed in the MTXrA line, which lacks a functional endogenous carrier to obtain the MTXrA-R16 clonal derivative. Influx was increased approximately 9-fold in MTXrA-R16 cells without a change in Km. The efflux rate constant was increased by a factor of 5.1 relative to L1210 cells, and this resulted in only a 2.1-fold increase in the steady-state level of free intracellular MTX, [MTX]i, when [MTX]e was 1 microM. The concentrative advantage for RFC1 (the ratio of [MTX]i in MTXrA-R16 to L1210 cells) increased from 1.8 at 0.1 microM MTX to 3.8 at an [MTX]e level of 30 microM. Augmented transport in MTXrA-R16 cells was accompanied by a 2-fold increase in accumulation of MTX polyglutamate derivatives and a approximately 50% decrease in the EC50 for 5-formyltetrahydrofolate and folic acid and the MTX IC50 relative to L1210 cells. These alterations paralleled changes in [MTX]i and not the much larger change in influx at low [MTX]e levels, consistent with the critical role that free intracellular folates and drug play in meeting cellular needs for folates and as a determinant of antifolate activity, respectively. The data indicate that RFC1 produces a large and near symmetrical increase in the bidirectional fluxes of MTX resulting in only a small increase in the transmembrane chemical gradient at low extracellular folate levels. Hence, increased expression of RFC1, alone, may not be an efficient adaptive response to folate deprivation, and other factors may come into play to account for the marked increases in concentrative folate transport which occur when cells are subjected to low folate-selective pressure.

[Comparison of plasma thyroxin and insulin concentrations between 10-day old layer and broiler chickens]

In this study both sexes of 10 day old layer and broiler chickens were used to investigate plasma circulating concentrations of 3,3'-5-triiodothyronine (T3), thyroxine (T4) and insulin by using the radioimmunoassay (RIA) methods. The results were as follows: serum T3 concentration was higher in broilers than that in layers (P < 0.01), especially a significant difference between male strains was seen in this experiment (P < 0.001), and the levels of plasma insulin was significantly higher in male broilers than that in male layers (P < 0.001), however, no clear differences in plasma T4 was seen between strains and sexes (P > 0.05). In addition, there were sex differences in T3 and insulin levels in layers, that is to say, those in the female layers was higher than those in the male layers, but no clear deifference was seen between sexes in broilers. A significant positive correlation between T3, insulin and their weight gained (P < 0.05). The results suggest that the levels of serum T3 and Insulin may influence the various growth rate during early posthatch development in layers and broilers.

[In situ hybridization for interleukin 4 and interleukin 5 messenger RNA in asthma]

The actual mechanism by which a group of asthmatics were resistant to glucocorticoids therapy remains poorly understood. Previous in vitro studies suggested that the pattern of cytokine gene expression may play a role in determining steroid resistance. In the current study, we used the technique of mRNA in situ hybridization to examine whether peripheral blood mononuclear cells (PBMCs) from steroid-resistance (SR) asthmatics vs. Steroid-sensitive (SS) asthmatics expressed different patterns of cytokines, particularly after treatment with steroid. PBMCs from SR patients did not differ significantly from those of SS in terms of their number expressing Interleukin (IL)-4 mRNA and IL-5 mRNA (P > 0.05) by culture alone. There were no differences in the number of PBMCs expressing IL-4 mRNA and IL-5 mRNA (P > 0.05) between incubation in the absence and presence of dexamethasone (DXM, 10(-7) mol/L) in SR. SS patients had a significant dicrease in the number of PBMCs expressing IL-4 mRNA and IL-5 mRNA (P < 0.01) after culture in the presence of DXM as compared with incubation in media alone. Our findings indicate that SR asthma is associated with a dysregulation of the expression of the genes encoding for IL-4 and IL-5.

[9-cis retinoic acid induces apoptosis in HL-60 cells]

OBJECTIVE

To investigate the apoptosis of HL-60 cells induced by 9-cis retinoic acid (9-cis RA), and illustrate the possible molecular mechanism.

METHODS

Apoptosis was detected by morphological observation, DNA electrophoresis and flow cytometric cell cycle analysis. Bcl-2 expression was detected by flow cytometry.

RESULTS

9-cis RA initiated apoptosis of HL-60 cells after inducing them irreversibly commited to differentiation. Bcl-2 was downregulated during the differentiation and apoptosis process. 9-cis RA was more potent than all-trans retinoic acid (ATRA) did in inducing terminal differentiation associated apoptosis and in downregulation of Bcl-2 expression.

CONCLUSION

9-cis RA can induce apoptosis in HL-60 cells. Downregulation of Bcl-2 expression appears to play an important role in the apoptosis of the differentiated leukemic cells.

[Scale-up preparation of hydrophobic interaction chromatographic packing materials based on inorganic matrix]

Based on inorganic matrix controlled pore glass (CPG) and macro-pore silica sphere, by using polyethylene glycol (PEG 1000) as a ligand, a preparation method of hydrophobic interaction chromatographic (HIC) packing material was improved by adding a proper catalyst during the bonding process. The packing material can be synthesized in a scale-up batch, for example 150g for each batch, both for analytical and preparative columns. The retention of proteins, such as cytochrome C (Cyt-C), chymotrypsingen-A (Chy-A), lysozyme (Lys) and ribonuclease(Rnase), is increased with the increasing of (NH4)2SO4 concentration in the eluant 2.5 mol/L of salt concentration for the mobile phase was chosen by considering the separation efficiency and equipment life. After comparing the effect of pH for the retention of proteins it is found that the proteins are well separated at pH 7. The time of linear gradient elution program was optimized in considering the separation efficiency and speed. It is better to take 30 minutes of the gradient program for the separation. Six standard proteins can be well separated with the high-performance HIC column in the linear gradient elution program from 2.5 to 0 mol/L of (NH4)2SO4 in 50 mmol/L of phosphate buffer solution within 30 minutes. Cyt-C, Rnase, Lys and Chy-A can be separated by the HIC column based on CPG matrix. Six proteins, Cyt-C, Rnase, Lys, Chy-A, insulin(Ins) and lipase (Lip) can be well separated on the column based on silica matrix with gradient elution program. The recovery of trypsin detected with BAEE method is over 95% after purification with the HIC column.

[Somatostatin and its secretory cells in tumor surrounding mucosa in colorectal cancer patients and its significance]

The somatostatin (SS) levels in tumor surrounding mucosae were determined by RIA, and the SS secretory cells in these tissues were observed by immunocytochemistry in colorectal cancer patients. The mean SS level was higher in cancer-adjacent mucosa (CAM, 0-2 cm from the tumor) than in cancer-distant mucosa (CDM, about 5 cm from the tumor), and in CAM without atypical hyperplasia than in such mucosa with different grades of atypical hyperplasia (P < 0.01). In CAMs, there was a very significant negative correlation between the SS level and cell dysplasia (P < 0.01). The form and location of SS cells in all tumor surrounding mucosae were similar to the normal. Both the mean SS cell number and total positive degree were very significantly higher in CAM than CDM (P < 0.01). SS levels in CAMs were correlated positively with the SS cell numbers and the total positive degrees in CAM (P < 0.01). It is concluded that the elevation of SS level in CAM is mainly caused by the increase of SS cells, which secrete more SS. The change of SS in colorectal cancer surrounding mucosa may play an important role in inhibiting the development of CAM atypical hyperplasia or the tumor, and is a local defensive reaction in the body.

[Toxoplasmosis infection in pregnant women in Lanzhou]

OBJECTIVE

To investigate toxoplasmosis (TOX) infection in pregnant women.

METHODS

The blood samples from 1,250 pregnant women were tested by indirect hemaglutination (IHA) for TOX. 1,327 normal cases were included in control group.

RESULTS

The infection rate of TOX was 7.28% and 8.14% in the study and control group respectivity. There was no significant difference between the study group and control group (P > 0.05). There was no marked relationship between various age groups. (P > 0.05). No significant difference was noted in three gestational periods. Most pregnant women with of TOX infection were active and recent.

CONCLUSION

Pregnancy did not increase the chance of TOX infection.

The refined structure of human rhinovirus 16 at 2.15 A resolution: implications for the viral life cycle

BACKGROUND

Rhinoviruses belong to the picornavirus family and are small, icosahedral, non-enveloped viruses containing one positive RNA strand. Human rhinovirus 16 (HRV16) belongs to the major receptor group of rhinoviruses, for which the cellular receptor is intercellular adhesion molecule-1 (ICAM-1). In many rhinoviruses, one of the viral coat proteins (VP1) contains a hydrophobic pocket which is occupied by a fatty acid-like molecule, or so-called 'pocket factor'. Antiviral agents have been shown to bind to the hydrophobic pocket in VP1, replacing the pocket factor. The presence of the antiviral compound blocks uncoating of the virus and in some cases inhibits receptor attachment. A refined, high-resolution structure would be expected to provide further information on the nature of the pocket factor and other features previously not clearly identified.

RESULTS

The structure of native HRV16 has been refined to a resolution of 2.15 A. The hydrophobic pocket in VP1 is observed in two alternative conformations. In one of these, the pocket is filled by a pocket factor and the protein structure is similar to virus-antiviral compound complexes. In the other conformation, the hydrophobic pocket is collapsed and empty. RNA bases stack against both a tryptophan and a phenylalanine residue on the internal surface of the viral capsid. Site-directed mutagenesis of the tryptophan, which is conserved across the picornaviruses, to nonconservative residues results in non-viable virus. Five symmetry-related N termini of coat protein VP4 form a ten-stranded, antiparallel beta barrel around the base of the icosahedral fivefold axis. The N termini of VP1 are amphipathic alpha helices, which stack on the outside of this beta barrel. The N termini of VP1 and VP4 have not been observed previously in rhinovirus structures.

CONCLUSIONS

The observation of a partially occupied hydrophobic pocket in HRV16 forms a missing link between HRV14, which is always observed with no pocket factor in the native form, and rhinovirus 1A and other picornaviruses (e.g. poliovirus, coxsackievirus) which contain pocket factors. The pocket factor molecules probably regulate viral entry, uncoating and assembly. Picornavirus assembly is known to proceed via pentamers, therefore, the interaction of RNA with the conserved tryptophan residues across twofold axes between pentamers may play a role in picornavirus assembly. The positioning of a cation on the icosahedral fivefold axes and the structure of the N termini of VP4 and VP1 around these axes suggest a mechanism for the uncoating of rhinoviruses.

Enhanced DNA alkylation activities of Hoechst 33258 analogues designed for bioreductive activation

A series of analogues of Hoechst 33258, designed to be subject to bioreductive activation, were synthesized, and interactions between these compounds and pBR322 DNA were investigated. Compounds containing a quinone group reacted with DNA via two possible pathways in the presence of reductants NADH or NADPH: radical cleavage and DNA alkylation. The corresponding dimethoxy compounds, which are not subject to reduction, showed very weak DNA binding ability. The strength of alkylation reaction of the quinone derivatives is related to leaving group ability. Furthermore, the quinone compounds preferentially alkylate DNA at 5'-CG and TG sequences rather than at the AT sites preferred as binding sites of Hoechst 33258.

[The expression of IL-1 alpha gene in gingival tissue]

IL-1 is secreted by a variety of cells and plays an important role in the network of cytokines. In this study, the expression of IL-1 alpha in gingival tissue was determined with reverse transcription-polymerase chain reaction (RT-PCR). The PCR-product was confirmed by DNA sequencing. The results showed that IL-1 alpha transcription was detected in all 5 inflammatory gingival tissue samples, but it was not delected in the normal gingival tissue samples and in the samples after treatment. These findings suggested that IL-1 alpha may be a specific indicator of periodontal disease, and a potential mediator in pathogenesis of periodontitis.

Camptothecin and minor-groove binder hybrid molecules: synthesis, inhibition of topoisomerase I, and anticancer cytotoxicity in vitro

The synthesis, characterization, inhibitory activity against topoisomerase I, and biological evaluation of a series of 14 camptothecin derivatives of polypyrrolecarboxamide (lexitropsin) conjugates of two structural classes: (A) camptothecin-NHCO-lexitropsin 44-51 and (B) camptothecin-CONH-lexitropsin 38-43 are described. All 16 compounds tested, 14 conjugates plus two functionalized camptothecin controls, inhibit topoisomerase I in the concentration range 1.12-16.6 microM that divide into three distinct categories based on activity. The most active enzyme inhibitors belong to structure class A with either cationic dimethylaminium or neutral amide end groups. Generally class B conjugates are less effective in inhibiting topoisomerase I. Cytotoxic potencies of the drugs was tested against four representative human tumor cell lines: SKOV3, SKLVB, HT29, and KB. All 16 drugs gave measurable IC50 values against the KB cell line and fell into two categories with IC50 values of 0.049-0.66 microM (largely structure class B) and 1.0-48 microM (largely class A). Thus the class B conjugates, while less potent against the enzyme, contain two of the most potent drugs, 38 and 39, against KB cell lines. In contrast, in the case of the cell lines SKOV3 and HT29 there was a general correlation between the better topoisomerase inhibitors and their cell cytotoxicities.

Cations in human rhinoviruses

All known crystal structures of rhinoviruses have some uninterpreted electron density on their fivefold axes at a distance of about 152 +/- 3 A from the viral center. This density had been assumed to be a Ca2+ ion, based on its shape, height, and the presence of Ca2+ ions in the crystallization solutions. Difference electron density maps between EGTA-soaked crystals of human rhinovirus 14 (HRV14), as well as HRV16, and their corresponding native structures show that this density is an EGTA-chelatable ion. Analysis of the coordination geometry indicates that the ions in HRV3, HRV14, and HRV1A could be Ca2+ and the ion in HRV16 might be Zn2+. These cations may play a role in regulation of rhinovirus stability, although the loss of the ion itself does not seem sufficient to lead to viral disassembly.

[A gas chromatographic method for determination of Butyraldehyde as a product of butanol biotransformation in rat liver]

Analysis of butyraldehyde obtained by the interaction of butanol with cytochrome P450 II E1 in rat liver microsomes prepared by centrifugation and with the NADPH added is described in this paper. The biotransformation rate of butanol into butyraldehyde can be used as an index for the assessment of the enzyme activity of cytochrome P450 II E1. A headspace gas chromatograghic method to determine the butyraldehyde has been developed. The detection limit and CV of this method for butyraldehyde in microsomes were 0.7 micromol/L and 8.1%-9.3% respectively. The recovery was 85.3%. The results show that this is a rapid and sensitive method with less interferences and fairly good precision. The method developed has made a reliable analytical methodological foundation for the assessment of the enzyme activity of cytochrome P450 II E1.

[GC-MS analysis of essential oils from the pericarps of Illicium majus Hook.f.et. Thoms. and I. micranthum Dunn]

The chemical constituents of essential oils from the pericarps of Illicium majus and I. micranthum were analyzed. Seventy-two compounds have been identified by GC-MS, of which safrole, linalool and limonene are higher in content.

A newly developed PCR assay of H. pylori in gastric biopsy, saliva, and feces. Evidence of high prevalence of H. pylori in saliva supports oral transmission

We have recently developed a new PCR assay for the detection of H. pylori. In this study, the polymerase chain reaction (PCR) assay was used to detect H. pylori in 88 gastric biopsy, 85 saliva, and 71 fecal specimens from 88 patients. H. pylori infection was confirmed in 71 of 88 patients by culture and/or histological stain of gastric biopsies. Serum IgG antibody to H. pylori was also measured and resulted in 97% sensitivity and 94% specificity. H. pylori DNA was detected by the PCR assay in gastric biopsy specimens from all 71 patients (100% sensitivity) with proven gastric H. pylori infection but not from 17 noninfected patients (100% specificity). In saliva specimens, H. pylori DNA was identified in 57 of the 68 patients (84%) with proven gastric H. pylori infection and in three of the 17 patients without gastric H. pylori infection. However, the PCR assay was only able to detect H. pylori DNA in the feces from 15 of 61 patients (25%) with proven gastric H. pylori infection and one of the 10 patients without gastric H. pylori infection. The results show that the PCR assay is reliable for detecting the presence of H. pylori in gastric biopsy and saliva specimens. The data indicate that H. pylori exists in a higher prevalence in saliva than feces and that the fecal-oral route may be an important means of transmission of this infection in developing countries but not as significant as previously suspected in the developed countries. It is likely that the oral-oral route is more prominent.

Human rhinovirus 3 at 3.0 A resolution

BACKGROUND

The over 100 serotypes of human rhinoviruses (HRV) are major causative agents of the common cold in humans. These HRVs can be roughly divided into a major and minor group according to their cellular receptors. They can also be divided into two antiviral groups, A and B, based on their sensitivity to different capsid-binding antiviral compounds. The crystal structures of HRV14 and HRV16, major-receptor group rhinoviruses, as well as HRV1A, a minor-receptor group rhinovirus, were determined previously. Sequence comparisons had shown that HRV14 seemed to be an outlier among rhinoviruses. Furthermore, HRV14 was the only virus with no cellular 'pocket factor' in a hydrophobic pocket which is targeted by many capsid-binding antiviral compounds and is thought to regulate viral stability. HRV3, another major-receptor group virus, was chosen for study because it is one of a subset of serotypes that best represents the drug sensitivity of most rhinovirus serotypes. Both HRV3 and HRV14 belong to antiviral group A, while HRV16 and HRV1A belong to antiviral group B.

RESULTS

HRV3 was found to be very similar to HRV14 in sequence and structure. Like HRV14, crystallized HRV3 also has no bound pocket factor. The structure of HRV3 complexed with an antiviral compound, WIN56291, was also determined and found to be similar to the same antiviral compound complexed with HRV14.

CONCLUSIONS

The amino-acid sequence and structural similarity between HRV3 and HRV14 suggests that rhinoviruses in the same antiviral group have similar amino-acid sequences and structures. The similar amino-acid composition in the pocket region and the viral protein VP1 N termini in all known group B HRV sequences suggests that these viruses may all contain pocket factors and ordered N-terminal amphipathic helices in VP1. Both of these factors contribute to viral stability, which is consistent with the observations that group B rhinoviruses have a higher chance of successful transmission from one host to another and is a possible explanation for the observed higher pathogenicity of these rhinoviruses.

Effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic acetylcholine receptors on transmembrane potentials and currents in guinea pig ventricular myocytes

The effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using whole-cell patch clamp technique. These effects were compared with those of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependent manner. By using a ramp or step rectangular pulse protocol, it was found that the antibodies increased the outward K+ current and decreased the inward basal ICa significantly. The reversal potential of both carbachol- and antibody-induced extra currents were close to -80 mV, being in proximity to the calculated Ek of -90 mV. A beta-adrenergic receptor agonist, isoprenaline, prolonged the action potential and increased the overshoot which could be inhibited by both antibody and carbachol. Isoprenaline increased inward ICa and outward Ik simultaneously. Both antibody and carbachol could significantly reduce the isoprenaline-stimulated ICa but not the isoprenaline-stimulated Ik. The antibody- or carbachol-induced outward K+ current and the depressant effects of antibody and carbachol on isoprenaline-stimulated ICa were partially antagonized by atropine. These results suggest that the anti-M2 muscarinic receptor antibodies display a stimulatory activity similar to muscarinic receptor agonist on the receptor-mediated electrophysiological events.

FliN is a major structural protein of the C-ring in the Salmonella typhimurium flagellar basal body

The Salmonella typhimurium FliN protein has been proposed to form a mutually interacting complex with FliG and FliM, the switch complex, that is required for flagellar morphogenesis and function. We have used affinity chromatography for purification of extended flagellar basal bodies sufficient for quantitative analysis of their protein composition. The belled, extended structure is predominantly comprised of the switch complex proteins; with FliN present in the most copies (111 +/- 13). This explains why single, missense fliN, fliG or fliM mutations, found in many non-motile strains, can alter the belled morphology. Cell lysates from these strains contained the wild-type complement of FliG, FliM and FliN; but the basal bodies lacked the outer, cytoplasmic(C)-ring of the bell and were separated by sedimentation from FliM and FliN. The amount of FliG present in basal bodies from wild-type and one such mutant, FliN100LP, was comparable. These data show that: (1) the mutations define a FliG and FliMFliN multiple contact interface important for motility. (2) FliG is responsible for the increased size of the membrane-embedded MS-ring complex of belled relative to acid-treated basal bodies. (3) FliN, together with FliM, account for most of the C-ring. As a major component of the C-ring, FliN is distinct from the other proteins implicated in axial flagellar protein export. Inner, cytoplasmic rod basal substructure, seen by negative-stain and quick-freeze replica electron microscopy, may gate such export. Lack of connectivity between the cytoplasmic rod and ring substructures places contacts between FliG and FliMFliN at the periphery of the basal body, proximal to the flagellar intramembrane ring particles. This topology is consistent with models where torque results from interaction of circumferential arrays of the switch complex proteins with the ring particles.

Transcription of dopamine D1A receptor mRNAs in rat heart

The existence of dopamine receptor subtypes in the heart has been suggested by pharmacological and biochemical techniques. So far, however, very little data is available as to the transcription of dopamine D1 subtype receptor genes in the heart. Therefore, in this study we employed reverse transcription-polymerase chain reaction (RT-PCR), which is a sensitive and highly specific method for identifying a low abundance mRNA in tissues, to determine if the D1A receptor gene was transcripted in the adult rat heart. Total RNA was isolated from the whole heart by the guanidium thiocyanate-CsCl method. Primers were based on the sequence of rat D1A cDNA cloned from the brain and corresponded to the third cytoplasmic loop of the receptor. A predicted size product (247bp) was evident from heart RNA. PCR performed in the absence of reverse transcriptase did not result in an amplification of the predicted product, indicating that these products were from cDNA and not from genomic DNA. The results demonstrate the existence of D1A receptor mRNA in the rat heart and that the D1A receptor in the heart are possibly identical to that from the brain. Since in this study the whole heart RNA was used, we cannot ascertain whether the mRNA comes from cardiac myocyte per se or from intermuscular coronary arterioles or from both.

Construction of an insecticidal baculovirus expressing insect-specific neurotoxin AaIT

Considering the factors which affect gene transcription, translation and the stability of mRNA, without changing the amino acid composition of the encoded polypeptide, AaIT gene encoding insect-specific neurotoxin was designed and synthesized according to bias in codon choice, overall G+C content and G+C content of bases at the third position in codons of polyhedrin genes of baculovirus and of plant genes as well. AaIT gene was fused behind a synthetic gp67 signal sequence and then recombined into the genome of Trichoplusia ni nuclear polyhedrosis virus (TnNPV) by transfer vector pSXIV VI+X3. The recombinant virus TnNPV-AaIT (occ+-gal-) was screened. The results of Southern blotting and SDS-PAGE demonstrated that AaIT gene had integrated into the genome of virus and expressed. Bioassays on the 3rd-instar Trichoplusia ni larvae showed that recombinant viruses TnNPV-AaIT could shorten the time of killing insect and improve the efficacy of killing agronomically important insects.

Expression of proliferating cell nuclear antigen in premalignant lesions of the larynx

PURPOSE

This study was performed to 1) evaluate the proliferative activity in premalignancies of the larynx by immunostaining for proliferating cell nuclear antigen (PCNA), 2) to examine the relationship between PCNA expression and histological diagnosis and 3) to evaluate clinical values of PCNA immunostaining.

MATERIALS AND METHODS

The percentage of PCNA-positive nuclei (PCNA index) and their highest location (PCNA grade) were evaluated in 44 specimens of premalignant lesions, 7 premalignant lesions near carcinomas, 9 normal epithelium, and 12 early invasive carcinomas of the larynx. Follow-up was conducted.

RESULTS

The mean of PCNA indices in premalignancies was significantly higher than in normal epithelium but lower than in early invasive carcinomas. PCNA index had no apparent correlation with the histological diagnosis, but in the same case, the higher degree of dysplasia showed higher PCNA index. PCNA grade showed significant correlation with the histological diagnosis. Cases with higher PCNA expression showed higher percentages of recurrence and cancerization. Premalignant lesions near carcinomas presented significantly high PCNA expression.

CONCLUSIONS

The proliferative activity in premalignancies of the larynx is higher than in normal epithelium and lower than in carcinomas. It differs from case to case, but in the same case the higher degree of dysplasia possesses higher proliferative activity. Dysplasia is associated with abnormal proliferation pattern. Special attention should be paid to those with abnormal proliferation patterns as well as high proliferative activity. PCNA immunostaining is of some referential value in predicting clinical outcome and guiding to make an early diagnosis of malignancy.

Insect-resistant tobacco plants expressing insect-specific neurotoxin AaIT

The recombinant plant expression vector pNGY-2 with designed and synthesized AaIT gene had been constructed. The AaIT gene was fused behind the sequence of TMV and inserted into expression vector under the control of two linked 35s promoters. The recombinant plasmid pNGY-2 was transferred into tobacco NC89 by agrobacterium-mediated transfer system. The GUS activity analysis and Southern blotting of regenerated plants indicated that AaIT gene had been integrated into tobacco genome. Insect bioassays showed that some transgenic plants had notable insect-resistant activity.

A study of the demographic characteristics of domestic tourists

"A sample survey was conducted [in China]: more than 6,000 questionnaires were submitted and retrieved from domestic tourists in Shanghai, Xi'ian, Huangshan, and Huashan in order to provide data for demographic analysis of the special fluid population of tourists. The paper looks at the relationship between tourists' gender, age, income, occupation, education, and family structure, as well as their tourist activity, selection of destinations, shopping, and other tourist behaviors."

FliG and FliM distribution in the Salmonella typhimurium cell and flagellar basal bodies

Salmonella typhimurium FliG and FliM are two of three proteins known to be necessary for flagellar morphogenesis as well as energization and switching of flagellar rotation. We have determined FliG and FliM levels in cellular fractions and in extended flagellar basal bodies, using antibodies raised against the purified proteins. Both proteins were found predominantly in the detergent-solubilized particulate fraction containing flagellar structures. Basal flagellar fragments could be separated from partially constructed basal bodies by gel filtration chromatography. FliG and FliM were present in an approximately equimolar ration in all gel-filtered fractions. FliG and FliM copy numbers, estimated relative to that of the hook protein from the early fractions containing long, basal, flagellar fragments, were (means +/- standard errors) 41 +/- 10 and 37 +/- 13 per flagellum, respectively. Extended structures were present in the earliest identifiable basal bodies. Immunoelectron microscopy and immunoblot gel analysis suggested that the FliG and, to a less certain degree, the FliM contents of these structures were the same as those for the complete basal bodies. These facts are consistent with the postulate that FliG and FliM affect flagellar morphogenesis as part of the extended basal structure, formation of which is necessary for assembly of more-distal components of the flagellum. The determined stoichiometries will provide important constraints to modelling energization and switching of flagellar rotation.

Apoptosis and c-jun induction by cisplatin in a human melanoma cell line and a drug-resistant daughter cell line

Cisplatin resistance was developed in the human melanoma cell line RPMI8322 by repeated short-term exposures to cisplatin. The most resistant daughter cell line, RPMI8322/CDDP-300, was 4-fold resistant to cisplatin, and partially cross-resistant to carboplatin, melphalan and UV, but not to BCNU. RPMI8322/CDDP-300 cells showed less apoptosis after cisplatin than the parental cells. The cisplatin resistance was not paralleled by a similar reduction in cellular cisplatin accumulation or DNA cross-links in RPMI8322/CDDP-300 cells, and these cells exhibited no increase in cellular glutathione or in mRNA encoding the DNA excision repair protein ERCC1 and XPB. Induction of c-jun mRNA by cisplatin was considerably lower in RPMI8322/CDDP-300 cells than in RPMI8322 cells, consistent with the possibility that c-jun induction may be involved in a pathway that triggers apoptosis after exposure to DNA damaging agents. However, c-jun induction is not necessary for apoptosis, since cisplatin also induced apoptosis in A14 rat embryo fibroblasts, cells in which the c-jun gene is deleted.

Structural effects of mutations in Salmonella typhimurium flagellar switch complex

Mutations in Salmonella typhimurium fliG, fliM and fliN give rise either to non-flagellate, non-motile or non-chemotactic mutant bacteria. The FliG, FliM and FliN proteins form part of recently characterized extended flagellar basal structures, and have been postulated to form a mutually interacting structural complex. We have examined basal body preparations from non-motile or non-chemotactic fliG, fliM and fliN mutant strains by electron microscopy and immunoblot gel analysis. Most flagellar preparations isolated from the non-motile mutants lacked FliM, but contained FliG. The basal bodies lacked the belled morphology characteristic of the wild-type structures, but had protrusions which could be labelled with anti-FliG. Non-motile mutant preparations severely depleted of FliG but containing FliM were also obtained. These preparations contained extended, belled flagellar structures that were labelled with anti-FliM. Thus, FliM is part of the shell of the extended structures responsible for the belled morphology, while FliG may be part of the inner substructure. The extended basal structures from a FliG temperature-sensitive mutant strain rapidly lost FliM, as well as FliG, upon a shift to a non-permissive temperature, implying interaction between the FliG- and FliM-containing substructures. In dramatic contrast to non-motile mutants, extended basal structures isolated from non-chemotactic mutants were indistinguishable from wild-type structures. This difference may reflect the energetics of the different protein-protein interactions operative during torque generation and the switching of rotation sense.

[Effects of Chinese ginseng root and stem-leaf saponins on learning, memory and biogenic monoamines of brain in rats]

The present investigation has shown that Ginseng root saponins (ig, 50mg/kg x 7d) facilitate the learning and memory of normal male Wistar rats, while the effect of Ginseng stem-leaf saponins (ig, 50mg/kg x 7d) on antielectrconvulsive shock-induced impairment of memory consolidation in rats is more intensive than that of root saponins. Both Ginseng root and stem-leaf saponins can significantly raise the levels of biogenic monoamines in normal rat's brain.

Conserved machinery of the bacterial flagellar motor

Novel periplasmic and cytoplasmic structural modules of the bases of bacterial flagella have been observed in situ and isolated using new biochemical protocols. Flagellar rotation may depend upon interactions of these modules with the intramembrane particle rings, a ubiquitous feature of flagellar bases necessary for torque generation. The outer membrane-associated basal disk of the Wolinella succinogenes polar flagellum has architecture well suited for interaction with the ring particles. However, antibody against the main W. succinogenes basal disk protein did not cross-react with flagella-enriched fractions from Salmonella typhimurium and Bacillus firmus; nor have such structures been observed in these species thus far. Antibodies against two S. typhimurium proteins, FliG and FliM, known to be involved in motor function and part of the cytoplasmic module in this species cross-reacted with flagella-enriched fractions from both W. succinogenes and B. firmus. In addition, flagellar cytoplasmic structure could be isolated from B. firmus. The basal disk may anchor the flagellar motor to the cell wall in some polar bacteria, but this does not seem to be a unique strategy. In contrast, the data indicate that the cytoplasmic module is conserved.

The purification and characterization of a human dual-specific protein tyrosine phosphatase

An expression and purification method was developed to obtain the recombinant human dual-specific protein tyrosine phosphatase (PTPase) VHR in quantities suitable for both kinetic studies and crystallization. Physical characterization of the homogeneous recombinant protein verified the mass to be 20,500 +/- 100 by matrix-assisted laser desorption mass spectrometry, confirmed the anticipated NH2-terminal amino acid sequence and demonstrated that the protein exists as a monomer. Conditions were developed to obtain crystals which were suitable for x-ray structure determination. Using synthetic diphosphorylated peptides corresponding to MAP177-189 (mitogen-activated protein) kinase (DHTG-FLpTEpYVATR), an assay was devised which permitted the determination of the rate constants for dephosphorylation of the diphosphorylated peptide on threonine and tyrosine residues. The diphosphorylated peptides are preferred over the singly phosphorylated on tyrosine by 3-8-fold. The apparent second-order rate constant kcat/Km for dephosphorylation of phosphotyrosine on DHTGFLpTEpYVATR was 32,000 M-1 S-1 while dephosphorylation of phosphothreonine was 14 M-1 S-1 (pH 6). The reaction of DHTGFLpTEpYVATR with VHR is ordered, with rapid dephosphorylation on tyrosine occurring first followed by slow dephosphorylation on threonine. Similar results were obtained with F(NLe)(N-Le)pTPpYVVTR, a peptide corresponding to a MAP kinase-like protein (JNK1(180-189)) which is involved in the stress response signaling pathway.

Highly insect-resistant transgenic tobacco plants containing both B.t. and CpTI genes

The cowpea trypsin inhibitor (CpTI) gene was synthesized according to its cDNA sequence using DNA synthesizer and confirmed by DNA sequencing. The CpTI gene and modified Bacillus thuringiensis (B.t.) delta-endotoxin gene were cotransformed to tobacco explants mediated by Agrobacterium tumefaciens. The integrations of B.t and CpTI genes were confirmed by PCR and Southern hybridization. Three kinds of transgenic plants were obtained: (1) containing CpTI gene, (2) containing B.t gene, (3) containing both CpTI and B.t genes. Bioassays showed that all these transgenic plants were toxic to the larvae of Heliothis armigera and that the tobacco plants containing both genes had enhanced toxicity to larvae by comparison with plants containing only CpTI or B.t gene.

Oral toxicity of boric acid and other boron compounds to immature cat fleas (Siphonaptera: Pulicidae)

Oral toxicity was characterized in first-instar cat fleas, Ctenocephalides felis felis (Bouché), feeding on dried blood treated with boric acid. LC50 values ranged from 2.11% after 24 h to 0.21% after 7 d. In carpet tests with five different boron compounds and a number of different formulations, significant mortality for first instars was observed in all cases. In similar tests with prepupae and cocoons, there was no significant effect on mortality. The importance of these results is discussed in light of current application procedures for boron compounds, and suggestions are made for future research.

[Direct determination of tin in water by oscillopolarography]

Sn(IV) has a sensitive polarographic wave in the system of H2SO4-KI-VitC-V (IV). We examined the factors influencing the polarographic wave and found that the concentration of sulfuric acid and temperature were critical factors for the determination. The sensitivity of the method was increased nearly 50-fold by decreasing the concentration of sulfuric acid from 0.8 mol/L to 0.1 mol/L. The coefficient of variation (CV) percentages of the method were less than 5% and 8% for 6-7 determinations of Sn (IV) standard and sample respectively. The recovery ranged from 97.3% to 101%. The proposed method is suitable for direct determination of trace Sn (IV) in most natural water samples.

Products, genetic linkage and limb patterning activity of a murine hedgehog gene

The hedgehog (hh) segmentation gene of Drosophila melanogaster encodes a secreted signaling protein that functions in the patterning of larval and adult structures. Using low stringency hybridization and degenerate PCR primers, we have isolated complete or partial hh-like sequences from a range of invertebrate species including other insects, leech and sea urchin. We have also isolated three mouse and two human DNA fragments encoding distinct hh-like sequences. Our studies have focused upon Hhg-1, a mouse gene encoding a protein with 46% amino acid identity to hh. The Hhg-1 gene, which corresponds to the previously described vhh-1 or sonic class, is expressed in the notochord, ventral neural tube, lung bud, hindgut and posterior margin of the limb bud in developing mouse embryos. By segregation analysis the Hhg-1 gene has been localized to a region in proximal chromosome 5, where two mutations affecting mouse limb development previously have been mapped. In Drosophila embryos, ubiquitous expression of the Hhg-1 gene yields effects upon gene expression and cuticle pattern similar to those observed for the Drosophila hh gene. We also find that cultured quail cells transfected with a Hhg-1 expression construct can induce digit duplications when grafted to anterior or mid-distal but not posterior borders within the developing chick limb; more proximal limb element duplications are induced exclusively by mid-distal grafts. Both in transgenic Drosophila embryos and in transfected quail cells, the Hhg-1 protein product is cleaved to yield two stable fragments from a single larger precursor. The significance of Hhg-1 genetic linkage, patterning activity and proteolytic processing in Drosophila and chick embryos is discussed.

The prokaryotic thermophilic TF1-ATPase is functionally compatible with the eukaryotic CFo-part of the chloroplast ATP-synthase

The ATP synthase from chloroplasts, CFo.F1, was reconstituted into liposomes, from which most of CF1 was removed by a short treatment with guanidinium chloride. ATP-dependent proton uptake was restored with these CFo-liposomes even better by the addition of the bacterial TF1-than of the related CF1-part. This proton uptake was prevented by tentoxin, a specific inhibitor of the CF1-ATPase, in these CFo.F1-liposomes, but not in the hybrid CFo.TF1-liposomes. Venturicidin, a specific inhibitor of proton flow through CFo, was able to block it in both the hybrid CFo.TF1-liposomes and reconstituted CFo.F1-liposomes. These results indicate that the bacterial TF1-part binds to the eukaryotic CFo-part of four subunits forming a functional CFo.TF1-ATPase.

The structure of human rhinovirus 16

BACKGROUND

Rhinoviruses and the homologous polioviruses have hydrophobic pockets below their receptor-binding sites, which often contain unidentified electron density ('pocket factors'). Certain antiviral compounds also bind in the pocket, displacing the pocket factor and inhibiting uncoating. However, human rhinovirus (HRV)14, which belongs to the major group of rhinoviruses that use intercellular adhesion molecule-1 (ICAM-1) as a receptor, has an empty pocket. When antiviral compounds bind into the empty pocket of HRV14, the roof of the pocket, which is also the floor of the receptor binding site (the canyon), is deformed, preventing receptor attachment. The role of the pocket in viral infectivity is not known.

RESULTS

We have determined the structure of HRV16, another major receptor group rhinovirus serotype, to atomic resolution. Unlike HRV14, the pockets contain electron density resembling a fatty acid, eight or more carbon atoms long. Binding of the antiviral compound WIN 56291 does not cause deformation of the pocket, although it does prevent receptor attachment.

CONCLUSIONS

We conjecture that the binding of the receptor to HRV16 can occur only when the pocket is temporarily empty, when it is possible for the canyon floor to be deformed downwards into the pocket. We further propose that the role of the pocket factor is to stabilize virus in transit from one host cell to the next, and that binding of ICAM-1 traps the pocket in the empty state, destabilizing the virus as required for uncoating.

Mechanisms of quenching of the fluorescence of a benzo[a]pyrene tetraol metabolite model compound by 2'-deoxynucleosides

The hydrophobic interactions of bulky polycyclic aromatic hydrocarbons with nucleic acid bases and the formation of noncovalent complexes with DNA are important in the expressions of the mutagenic and carcinogenic potentials of this class of compounds. The fluorescence of the polycyclic aromatic residues can be employed as a probe of these interactions. In this work, the interactions of the (+)-trans stereoisomer of the tetraol 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT), a hydrolysis product of a highly mutagenic and carcinogenic diol epoxide derivative of benzo[a]pyrene, were studied with 2'-deoxynucleosides in aqueous solution by fluorescence and UV spectroscopic techniques. Ground-state complexes between BPT and the purine derivatives 2'-deoxyguanosine (dG), 2'-deoxyadenosine (dA), and 2'-deoxyinosine (dI) are formed with association constants in the range of approximately 40-130 M(-1). Complex formation with the pyrimidine derivatives 2'-deoxythymidine (dT), 2'-deoxycytidine (dC), and 2'-deoxyuridine (dU) is significantly weaker. Whereas dG is a strong quencher of the fluorescence of BPT by both static and dynamic mechanisms (dynamic quenching rate constant k(DYN) = [2.5 +/- 0.4] x 10(9) M(-1)s(-1), which is close to the estimated diffusion-controlled value of approximately 5 x 10(9) M(-1)s(-1), both dA and dI are weak quenchers and form fluorescence-emitting complexes with BPT. The pyrimidine derivatives dC, dU, and dT are efficient dynamic fluorescence quenchers (k(DYN) approximately [1.5-3.0] x 10(9) M (-1)s(-1), with a small static quenching component due to complex formation evident only in the case of dT. None of the four nucleosides dG, dA, dC and dT are dynamic quenchers of BPT in the triplet excited state; the observed lower yields of triplets are attributed to the quenching of single excited states of BPT by 2'-deoxynucleosides without passing through the triplet manifold of BPT. Possible fluorescence quenching mechanisms involving photoinduced electron transfer are discussed. The strong quenching of the fluorescence of BPT by dG, dC and dT accounts for the low fluorescence yields of BPT-native DNA and of pyrene-DNA complexes.

Fluorescence HPLC methods for detecting benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide-deoxyadenosine adducts in enzyme-digests of modified DNA: improved sensitivity

The fluorescence of mononucleoside adducts derived from the binding of anti-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo [a]pyrene (BPDE I) to N6-deoxyadenosine (BPDE-dA adducts) is 10-100 times stronger (depending on the methanol/water solvent composition) than the fluorescence of adducts derived from the binding of this diol epoxide derivative to N2-deoxyguanosine. It is shown here that these fluorescence characteristics can be used to quantitate the relatively low yields of BPDE-dA adducts by fluorescence detection when BPDE-modified DNA is subjected to enzymatic degradation to the mononucleoside levels, followed by HPLC analysis of the digests.