Glucuronidation in the polar bear (Ursus maritimus)

Polar bears bioaccumulate lipophilic pollutants, including polychlorinated biphenyls (PCBs), into their bodies from their exclusive diet of marine organisms. Hydroxylated PCB metabolites (OH-PCBs) have been found in plasma, presumably due to CYP-dependent biotransformation of PCBs in liver. Little is known about the phase 2 metabolism of hydroxylated xenobiotics in polar bears. The objective of this study was to examine UDP-glucuronosyltransferase (UGT) activity with OH-PCBs and a hydroxylated polycyclic aromatic hydrocarbon, 3-hydroxy-benzo(a)pyrene (3-OH-BaP), in polar bear liver. Samples of frozen polar bear liver were used to prepare microsomes. UGT activity with 3-OH-BaP in Brij-treated microsomes, measured by a fluorescence assay, was readily measurable with protein concentrations in assay tubes of up to 10 μg/ml, but dropped off very sharply at higher protein concentrations. The apparent K_m for 3-OH-BaP was 1.71 ± 0.04 μM, and V_max 1.26 ± 0.16 nmol/min/mg protein (mean ± SD, n=3). UGT activities with a model tetrachloro-OH-PCB (4^′-OH-CB72) and a model hexachloro-OH-PCB (4^′-OH-CB159) were assayed with [¹⁴-C]-UDPGA and separation of the [¹⁴-C]-glucuronide by ion-pair extraction and thin-layer chromatography. [¹⁴-C]-glucuronide conjugates were readily formed by polar bear liver microsomes in the absence of added substrate, apparently from contaminants present in liver. This phenomenon was not observed using hepatic microsomes from laboratory-held catfish. Glucuronidation efficiency was much higher with 4^′-OH-CB72 (K_m 7.3 μM; V_max 1.55 nmol/min/mg) than 4^′-OH-CB159 (K_m 16.1 μM; V_max 0.46 nmol/min/mg). The identities of the aglycones present in polar bear liver are not known, but could include OH-PCBs or hydroxylated metabolites of other persistent organic pollutants. This study demonstrates that UGT with high activity for 3-OH-BaP and other substrates is present in polar bear liver.     

Increased toxicity of benzo(a)pyrene-7,8-dihydrodiol in the presence of polychlorobiphenylols

Benzo(a)pyrene (BaP) and polychlorinated biphenyls (PCBs) often co-exist in contaminated environments. Polychlorobiphenylols (OH-PCBs), formed by CYP-dependent monooxygenation of PCBs, are potent inhibitors of the glucuronidation of hydroxylated BaP metabolites. We hypothesized that OH-PCBs could drive the biotransformation of (-)BaP-7,8-dihydrodiol (BaP-7, 8-D) away from detoxication and towards formation of the reactive metabolite. A mixture of five OH-PCBs with 4-6 Cl atoms was infused into isolated, perfused, biliary intact livers (n=3 fish) removed from 3-methylcholanthrene-induced channel catfish. Controls (n=3) were infused with vehicle. Subsequently, [3H]-BaP-7, 8-D was infused into each liver and bile was collected for 1 h. The livers were taken for analysis of metabolites and DNA adducts. Induction status was confirmed by EROD assay. Bile was analyzed for metabolites. It was found that preinfusion of the mixture of OH-PCBs reduced the extent of glucuronidation of BaP-7, 8-D and increased the formation of DNA adducts 5-fold over controls. GSH conjugates, tetrols and triols were increased in the OH-PCB-infused fish, providing further support for our hypothesis that if the glucuronidation were inhibited, CYP-dependent activation would increase. These studies suggest a mechanism for synergy of toxicity of PAH and PCBs.     

Increased toxicity of benzo(a)pyrene-7,8-dihydrodiol in the presence of polychlorobiphenylols

Benzo(a)pyrene (BaP) and polychlorinated biphenyls (PCBs) often co-exist in contaminated environments. Polychlorobiphenylols (OH-PCBs), formed by CYP-dependent monooxygenation of PCBs, are potent inhibitors of the glucuronidation of hydroxylated BaP metabolites. We hypothesized that OH-PCBs could drive the biotransformation of (−)BaP-7,8-dihydrodiol (BaP-7, 8-D) away from detoxication and towards formation of the reactive metabolite. A mixture of five OH-PCBs with 4–6 Cl atoms was infused into isolated, perfused, biliary intact livers (n=3 fish) removed from 3-methylcholanthrene-induced channel catfish. Controls (n=3) were infused with vehicle. Subsequently, [³H]-BaP-7, 8-D was infused into each liver and bile was collected for 1 h. The livers were taken for analysis of metabolites and DNA adducts. Induction status was confirmed by EROD assay. Bile was analyzed for metabolites. It was found that preinfusion of the mixture of OH-PCBs reduced the extent of glucuronidation of BaP-7, 8-D and increased the formation of DNA adducts 5-fold over controls. GSH conjugates, tetrols and triols were increased in the OH-PCB-infused fish, providing further support for our hypothesis that if the glucuronidation were inhibited, CYP-dependent activation would increase. These studies suggest a mechanism for synergy of toxicity of PAH and PCBs.     

Sulfation and glucuronidation of benzo[a]pyrene-7,8-dihydrodiol in intestinal mucosa of channel catfish (Ictalurus punctatus).

Intestinal metabolism plays a significant role in the bioavailability of ingested environmental toxicants. In this study, the potential for first pass, phase 2 biotransformation of benzo[a]pyrene-7,8-dihydrodiol (BaP-7,8-diol) in intestinal mucosa was examined. Sulfotransferase and Uridine 5'-Diphospho-Glucuronyl-transferase activity were measured in cytosol, and microsomes respectively. Radiolabeled conjugation products were analyzed by TLC and high-performance liquid chromatography (HPLC). The results indicated that BaP-7,8-diol was a poor substrate for intestinal sulfotransferase. Vmax for the sulfation of BaP-7,8-diol was 0.002 nmol mg-1 min-1, which is at least three orders of magnitudes lower than the Vmax for phenolic BaP metabolites. Studies with 3'phosphoadenosine-5' phosphosulfate (PAP)-35S as co-substrate showed that an unidentified compound in the reaction mixture was sulfated, dependent on the BaP-7,8-diol concentration. This could indicate that BaP-7,8-diol was interacting with a regulatory site on the enzyme and stimulated sulfation of an endogenous molecule in cytosol. Kinetic analysis of microsomal glucuronidation resulted in a Vmax of 0.30 nmol mg-1 min-1 (+/- 0.06 S.D., n = 4), with a Km of 23.39 microM (+/- 2.66 S.D.). The Km for the co-substrate UDP-glucuronic acid was approximately 43 microM. The slow rates for sulfation and glucuronidation of BaP-7,8-diol may explain its relatively high systemic availability when ingested or produced by intestinal phase 1 enzymes.     

Polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) in livers of harbor seals (Phoca vitulina) from San Francisco Bay,California and Gulf of Maine

Bioaccumulation of endocrine disruptors in marine mammals positioned at the top of the food chain is of toxicological concern. Livers from four pups and ten adult harbor seals (Phoca vitulina) stranded in San Francisco Bay (SFB) and the Gulf of Maine (GOM) were analyzed for polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs). We used GC–ECD and GC–NCI/MS to investigate the presence of 28 PCBs and 8 OH-PCB metabolites, respectively. Σ₂₈PCB concentrations (di- to octa-CBs) ranged from 1.81 to 35.9 μg/g lipid with a median of 6.53 for the seal pups and 2.31 to 249 μg/g lipid with a median of 28.9 for the adult seals. Σ₈OH-PCB concentrations (penta- to hepta-OH-PCBs) ranged from 0.02 to 0.69 μg/g lipid with a median of 0.04 for the adult seals, i.e., at much lower concentrations than those for PCBs. Ratios of OH-PCBs to PCBs (0.24% on average) were comparable to those in beluga whale, but were lower than ratios in human livers. The OH-PCB profiles were slightly different between SFB and GOM seal livers, although similar PCB congener patterns were observed. Generally, 4-OH-CB107 was found predominantly in seal livers and was the only OH-PCB detectable in most of seal pup livers. This study provides information on OH-PCBs in seals, adding to the scarce exposure data for these chemicals.     

Sweeping scientific data under a polar bear skin rug: The IUCN and the proposed listing of polar bears under CITES Appendix I

In 2008 the US Government listed the polar bear as “threatened” under the US Endangered Species Act, largely due to scientific analyses of climate change data and polar bear distribution conducted by the US Geological Survey (USGS), which projected a 2/3 reduction in the polar bear population within the next 40 years. In 2009 the US Government announced that it would submit a proposal to the 15th Conference of the Parties to the Convention on International Trade in Endangered Species of Wild Fauna and Flora to uplist polar bears from CITES Appendix II to Appendix I. A report produced by the IUCN/Traffic stated that this was not warranted. However, the IUCN/Traffic report did not consider the USGS data noted above. Ultimately the proposal for CITES uplisting failed. In this paper we examine the differences in the IUCN/Traffic report and the best available science, and conclude that listing polar bears under CITES Appendix I was scientifically warranted.     

Polar bears and CITES: A rejoinder to Parsons and Cornick

In 2010 a US proposal to uplist polar bears to Appendix I of CITES was rejected. Parsons and Cornick (2011, [1]) critiqued this decision and the IUCN/TRAFFIC analysis that supported it. Their critique overlooks several important dimensions of polar bear conservation. Foremost, they failed to explore what subsistence hunting actually means in this context. Paradoxically, prohibiting international trade through CITES might actually increase the number of bears killed by northern Aboriginal peoples. Second, they misread the scope of the IUCN/TRAFFIC recommendation. Third, uplisting polar bears under CITES would allow national governments to claim they are saving polar bears through a decision that only addresses peripheral threats and diverts attention from insufficient action to mitigate climate change: the factor that Parsons and Cornick rightly point out as the primary threat to polar bears.     

Biological transport and mammal to mammal transfer of organochlorines in Arctic fauna

Ringed seal (Phoca hispida) is assumed to be the most important and common prey of polar bears (Ursus maritimus). However, during a scientific survey in the ice area of the northern Barents Sea east of Svalbard in June 1995, an unexpectedly high number of polar bears were observed feeding on harp seal (Phoca groenlandica) carcasses. Samples of both harp and ringed seals were obtained and organochlorine (OC) occurrence and pattern in these two potential polar bear prey species were determined. Significantly higher OC concentrations were found in harp seals, as compared to the ringed seals. All animals in the northern harp seal group were lean specimens in late moult. The industrial chemicals, polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB), and the OC pesticides bis-2,2,(chlorophenyl)-1,1,1-trichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), and chlordanes (CHLORs) were analysed in blubber. The concentrations of sigma PCB (sum of concentrations of 16 PCB congeners) and sigma DDT (sum of concentrations of p,p'-DDT and p,p'-DDE) in the northern harp seal group ranged from 2093 to 20,382 and 1460 to 10,381 ng g-1 lipid weight, with mean concentrations of 11,133 and 6847 ng g-1 lipid weight, respectively. The mean concentrations of the CHLORs, oxychlordane and trans-nonachlor, were 1311 and 3743 ng g-1 lipid weight, respectively, while the mean concentrations of HCB and HCH isomers (alpha-, beta- and gamma-HCH) were all < 500 ng g-1 lipid weight. No significant difference was found in the mean total blubber mass between the two seal species when collected in June. This indicates that polar bears preying on harp seals instead of ringed seals at this time of the year could accumulate significantly higher PCB concentrations. We suggest that polar bears feeding along the ice-edge east of Svalbard in May and June preferentially prey on harp seals instead of ringed seals, and that this may partly explain the variation in PCB concentrations among polar bears from the Norwegian Arctic. An hypothesis is that the harp seal may function as a transport vector of OCs into the high Arctic environment.     

Kinetic and toxicological characteristics of acetylcholinesterase from the gills of oysters (Crassostrea rhizophorae) and other aquatic species

The aim of this work was to characterize the cholinesterases from gills of Crassostrea rhizophorae in order to use them as biomarkers. Gills were homogenized and then centrifuged (9,000 x g, 4 degrees C, 30 min). S9 and Triton X-100 S9 treated (TX S9) fractions were employed as enzyme source. Km(ap) and Vmax were estimated, using acetylthiocholine iodide as substrate. Inhibition assays were performed with iso-OMPA and eserine. The Km(ap) for S9 and TX S9 fractions were 0.05 and 0.06 mM, whereas the Vmax were 1.92 and 5.84 nmol/min/mg protein. respectively. No inhibition was detected when the samples were incubated with iso-OMPA, suggesting the presence of acetylcholinesterases (AChE) in oyster gill homogenates. Sensitivity to eserine inhibition of AChE in the gills of oysters is intermediate when compared with other aquatic species.     

Polar bear management,sport hunting and Inuit subsistence at Clyde River,Nunavut

This paper begins by reviewing the structure and evolution of polar bear (Ursus maritimus) management in Canada and in the Territory of Nunavut since the inception of the Agreement on the Conservation of Polar Bears in the 1970s. This is followed by the paper's main focus, the examination of the socio-economic and cultural importance of polar bears for Inuit and the success of the Agreement in supporting contemporary Inuit subsistence relations in Nunavut.     

DNA adducts in hematopoietic tissues and blood of the mummichog (Fundulus heteroclitus) from a creosote-contaminated site in the Elizabeth River, Virginia.

Hydrophobic DNA adducts were examined in liver, anterior kidney, spleen, and blood of tumor-prone mummichog (Fundulus heterclitus) from the creosote-contaminated Atlantic Wood (AW) site (Elizabeth River, Virginia). DNA adducts eluted in a diagonal radioactive zone, characteristic of polycyclic aromatic hydrocarbon exposure, in all examined tissues of AW fish. Mummichog demonstrated significantly higher levels of DNA adducts in spleen (394 +/- 109 nmol adducts/mol nucleotides) than in liver (201 +/- 77 nmol adducts/mol nucleotides) or anterior kidney (211 +/- 68 nmol adducts/mol nucleotides; P = 0.036). The levels of DNA adducts in the pooled blood (pool of four) were 142 nmol adducts/mol nucleotides. DNA adducts were not detected in the liver, anterior kidney, spleen and blood of fish collected from the reference site (< 2 nmol adducts/mol nucleotides). The high levels of DNA adducts detected in tissues of AW mummichog may be linked to the increased cancer incidence and immunosuppression in this population.     

Esterification of vertebrate-like steroids in the eastern oyster (Crassostrea virginica)

The esterification of two model vertebrate steroid hormones - estradiol (E2) and dehidroepiandrosterone (DHEA) - was studied in the oyster Crassostrea virginica. The activity of acyl-CoA:steroid acyltransferase was characterized in microsomal fractions isolated from oyster digestive glands. The apparent Km and Vmax values changed with the fatty acid acyl-CoA used (C20:4, C18:2, C18:1, C16:1, C18:0 or C16:0), and were in the range of 9-17 microM, and 35-74 pmol/min/mg protein for E2, and in the range of 45-120 microM, and 30-182 pmol/min/mg protein for DHEA. Kinetic parameters were also assessed in gonadal tissue. The enzyme saturated at similar concentrations, although conjugation rates were lower than in digestive gland. Preliminary data shows that tributyltin (TBT) in the low microM range (1-50) strongly inhibits E2 and DHEA esterification, the esterification of E2 being more sensitive to inhibition than that of DHEA. Overall, results indicate that apolar conjugation occurs in oysters, in both digestive gland and gonads, at a very similar rate to mammals, suggesting that this is a well conserved conjugation pathway during evolution. Esterification, together with other mechanisms, can modulate endogenous steroid levels in C. virginica, and might be a target for endocrine disrupters, such as TBT.     

Simultaneous exposure of English sole (Parophrys vetulus) to sediment-associated xenobiotics: Part 1—uptake and disposition of 14C-polychlorinated biphenyls and 3H-benzo[a]pyrene

English sole (Parophrys vetulus) were exposed to environmentally realistic levels of sediment-associated ³H-benzo[a]pyrene (3 μg BaP/g sediment, dry weight) and ¹⁴C-Aroclor 1254 (1 μg PCBs/g), separately and together, for up to 10 days. BaP and its metabolites in tissues reached steady-state concentrations by the first day of the exposure, whereas PCBs did not approach steady-state concentrations until the tenth day of exposure. Simultaneous exposure of sole to BaP and PCBs, relative to separate exposure to the xenobiotics, significantly increased the concentrations of BaP-derived radioactivity and decreased the concentrations of PCB-derived radioactivity in some tissues and bile. Accumulation of PCB-derived radioactivity, estimated as the burden in tissues, was significantly greater (4- to 13-fold) than that of BaP-derived radioactivity throughout the experiments and regardless of the type of exposure. The rank of the concentrations of PCB-derived radioactivity in tissues and bile was: bile ～ liver > brain > kidney ～ gill > skin ～ blood ～ muscle and for BaP-derived radioactivity the order was: bile > liver > gill > kidney > skin ～ blood > muscle > brain. BaP-derived radioactivity in liver and bile was present primary (85–99%) as metabolites, whereas PCB-derived radioactivity was present equally as parent compounds and metabolites in bile and primarily (98 %) as parent compounds in liver. Hydrolysis of bile from PCB/BaP-exposed sole with β-glucuronidase/arylsulfatase released 35 % of the BaP-derived radioactivity and 32 % of the PCB-derived radioactivity as primary metabolites. A much higher proportion of the BaP-derived radioactivity (64 %) than the PCB-derived radioactivity (13 %) in bile was unaffected by the enzyme treatment, indicating differences in the conjugation of the primary metabolites of PCBs and BaP. The results suggest that in contaminated environments the tissue to sediment concentration ratios for PCBs would exceed that for BaP and its metabolites; however, BaP would be continually absorbed and metabolized by sole to potentially carcinogenic and mutagenic compounds. In addition, the tissue levels of these toxic compounds may be increased by simultaneous exposure to PCBs.     

Seasonal changes in phosphatase activities in Toulon Bay (France)

We studied the characteristics of the phosphatase activity (Km and Vmax) in total seawater and in particulate material of the three main plankton classes (0.25-5, 5-90 and >90 microm) in a coastal marine ecosystem of Toulon Bay (French Mediterranean Sea). The measurement of the hydrolysis of sodium paranitrophenylphosphate (pNPP), a substrate of phosphatase, revealed low and high affinity components in unfiltered seawater and in particulate matter. In unfiltered seawater, the low affinity activity was predominant from October to March during phytoplankton development. The high affinity activity dominated from April to June and was significantly correlated with the bacterial abundances. The phosphatase behaviour in the particulate material differs from that in the unfiltered seawater. The activity of the three particulate classes was generally much lower than that of unfiltered seawater, particularly the low affinity activity. The >90 microm size fraction consisted in greater part of zooplankton. In this size class, the activity (nmol l(-1) h(-1)) of the low affinity component was predominant from May to August, when the abundance of the larvae of copepods (copepodites) was highest. Its high specific activity (Activity/Protein concentration as nmol l(-1) h(-1) microg(-1)) was particularly elevated during this period. The 5-90 microm fraction consisted of phytoplankton cells, especially Dinoflagellates. Between September and January, the activity (nmol l(-1) h(-1)) of this size class was mostly supported by the low affinity component. The specific activity (nmol l(-1) h(-1) microg(-1)) of the high affinity component was highest in June and August. No significant correlation was found between phosphatase activities and chlorophyll a or total cell abundance. In return temporary relationships with specific taxa exist in particular with Ceratium spp., Gymnodinium spp. and Protoperidinium spp. The contribution of the 0.25-5 microm size class exceeded rarely 20% of the total particulate activity. Between June and August, high specific activities (nmol l(-1) h(-1) microg(-1)) were observed for its high affinity component. In autumn, strong rainfall increased the phosphate and nitrate concentrations and led to a drop in salinity, which probably explains the low phosphatase activities (nmol l(-1) h(-1)) and cell densities observed during this period.     

中华白海豚(Sousa chinensis)组织中多氯联苯的研究

以珠江口海域的两头中华白海豚为研究对象，采用气相色谱法分析了海豚组织中多氯联苯（PCBs）的含量分布特征和毒性水平。结果表明，PCBs在海豚10种不同组织中的含量范围为25．1—85567．3ng／g，PCBs含量最高的组织为额隆和皮肤，其次为肝脏、肌肉、心脏、睾丸和脑，最低的为肺、胃和肾脏；PCBs同系物和同族物在海豚不同组织中的分布特征相似，同系物中以PCB101＋113和PCB153所占总量的百分比最大，在10．25％-51．70％之间；在同族物中以含在同族物中以5个氯原子和6个氯原子的PCBs为主，所占百分比均在23．53％-60．06％之间；运用二蛞哄毒性当量（TEQ）评价了中华白海豚不同组织中PCBs的毒性，其TEQs范围为55．9—68191．0pg／g，其中皮肤TEQs含量最高。TEQs主要来自非邻位取代的PCBs，占总量的74．15％-99．62％，其中来自PCB126的占34．11％-96．5I％。与世界其他海域海豚的PCBs污染水平相比，成年中华白海豚受PCBs污染严重，其体内的PCBs含量和毒性当量均已超出安全浓度范围，对其健康已造成威胁。     

Altered glutathione S-transferase catalytic activities in female brown bullheads from a contaminated central Florida lake.

Brown bullheads (Ameriurus nebulosus) are a demersal freshwater species that can be found in a number of polluted ecosystems. The purpose of the present study was to determine the overall capacity for in vitro glutathione S-transferase (GST) detoxification by brown bullheads, and to see if bullhead GST catalysis was altered in bullheads from a polluted site. Brown bullhead liver cytosolic GSTs catalyzed the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) over a large range of substrate concentrations, with apparent Km and Vmax for CDNB at fixed nucleophile (glutathione, GSH) concentrations of 1.8-1.9 mM and 12.1-14.6 mumol CDNB conjugated/min/mg, respectively. Bullhead GSTs were also highly active toward other substrates such as ethacrynic acid (ECA), delta 5-androstene-3,17-dione (ADI), and nitrobutyl chloride (NBC). Initial rate GST catalytic activities toward CDNB, NBC, ECA, and ADI were significantly lower in female bullheads from a contaminated lake (Lake Apopka Marsh) as compared to female bullheads inhabiting a nearby control site (Lake Woodruff). No site differences were observed with respect to male bullhead GST activities. These studies suggest that brown bullheads efficiently carry out GST conjugation of diverse electrophilic substrates. However, bullhead GST catalysis may be compromised in bullheads inhabiting polluted ecosystems.     

北太平洋和北冰洋大气中多氯联苯的浓度与气固分配行为

Polychlorinated biphenyls(PCBs) were measured in atmospheric samples collected from the North Pacific to the Arctic Ocean between July and September 2012 to study the atmospheric concentration characteristics of PCBs and their gas/particle partitioning. The mean concentration of 26 ∑PCBs(vapor plus particulate phase)(∑PCBs) was 19.116 pg/m3 with a standard deviation of 13.833 pg/m3. Three most abundant congeners were CB-28,-52 and-77, accounting for 43.0% to ∑PCBs. The predominance of vapor PCBs(79.0% to ∑PCBs) in the atmosphere was observed. PCBs were negative correlated with the latitudes and inverse of the absolute temperature(1/T). The significant correlation for most congeners was also observed between the logarithm of gas/particle partition coefficient(log KP) and 1/T. Shallower slopes(from-0.15 to-0.46, average-0.27) were measured from the regression of the logarithm of sub-cooled liquid vapor pressures(logpo L) and log KP for all samples. The difference of the slopes and intercepts among samples was insignificant(p0.1), implying adsorption and/or absorption processes and the aerosol composition did not differ significantly among different samples. By comparing three models, the J-P adsorption model, the octanol/air partition coefficient(KOA) based model and the soot-air model, the gas/particle partitioning of PCBs in the Arctic atmosphere was simulated more precisely by the soot-air model, and the adsorption onto elemental carbon is more sensitive than the absorption into organic matters of aerosols, especially for lowchlorinated PCB congeners.     

In vitro mechanistic differences in benzo[a]pyrene-DNA adduct formation using fish liver and mussel digestive gland microsomal activating systems

Turbot (Scophthalmus maximus) and mussel (Mytilus edulis) microsomes were incubated with DNA to examine if microsomal in vitro metabolism of BaP could result in DNA adducts detected by 32P-postlabelling. Turbot DNA was incubated with benzo[a]pyrene (BaP), NADPH and microsomal activating systems prepared from either livers of unexposed turbot, turbot exposed to BaP or beta-naphthoflavone (beta-NF) or digestive glands from mussels. The beta-NF activating system generated the highest levels of DNA adducts detected in this study (451.7 adducts per 10(8) nucleotides) and were distributed in three discrete adduct TLC spots, one of which (97% of the total adducts) co-migrated with the 32P-postlabelled BaP 7,8-diol, 9,10-epoxide-N2-guanine adduct. Fewer adducts (P < 0.05) were generated by BaP-induced microsomes (9.4-30.6 adducts per 108 nucleotides) but levels were higher (P <0.05) than those generated from untreated fish (3.5 adducts per 10(8) nucleotides). Co-incubation with 500 microM alpha-naphthoflavone (alpha-NF) resulted in 97-99% inhibition in adduct formation implicating cytochrome P450-dependent (CYP) bioactivation however there was some evidence for carry over of BaP in the liver microsomal preparations from BaP injected fish. In contrast to the fish activating systems, no DNA adducts were observed when mussel microsomes were incubated with BaP, DNA and NADPH.     

钝顶螺旋藻的硝酸还原酶与氢酶之间的电子竞争

于1994年6－11月，运用生物化学方法以钝项螺旋藻为材料制备整体细胞和无细胞提取物。测定表明，整体细胞硝酸还原酶与氢酶活性的相互关系和无细胞提取物氢酶与硝酸还原酶的（对还原甲基紫精）Km值，分别为2．299×10－7mol／L和1．098×10－7mol／L；证实在硝酸还原酶与氢酶之间存在着电子竞争。