Effect of aroclor 1248 and two pure PCB congeners on phospholipase D activity in rat renal tubular cell cultures

This paper elucidates the effect of different polychlorinated biphenyls (PCBs) on the phospholipase D (PLD) activity in soluble and particulate fractions of rat renal proximal tubular culture cells. Treatment with Aroclor 1248 (a commercial PCB mixture) caused a marked increase in the activity of PLD in intact renal tubular cells. The PLD activity was increased by Aroclor 1248 in the particulate fraction while the enzyme activity was unaffected in the soluble fraction. This work also shows that PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl, a di-ortho-substituted nonplanar congener) can increase the activity of PLD only in the particulate fraction. The exposure of cell cultures to PCB 77 (3,3',4,4'-tetrachlorobiphenyl, a non-ortho-substituted planar congener) does not alter PLD activity. These results suggest that PCB effects are structure dependent. Therefore, in order to clarify the molecular mechanism of activation of PLD by PCBs, the contents of immunoreactive PLD were examined by immunoblot analysis. Renal tubular cells expressed a PLD protein of 120 kDa corresponding with the PLD1 mammalian isoform in both the particulate and the soluble fraction. Aroclor 1248, PCB 153, and PCB 77 do not induce changes in the levels of PLD protein. These data indicate that PCBs, particularly nonplanar congeners, increase PLD activity. Moreover, these changes could not be demonstrated in the enzyme content in rat renal tubular cell cultures.     

Redistribution of cPLA(2) in rat renal tubular cell cultures in response to PCBs

The influence of different polychlorinated biphenyls (PCBs) upon the cytosolic phospholipase A(2) (cPLA(2)) redistribution to the particulate fraction has been investigated in rat renal proximal tubule culture cells. Treatment with Aroclor 1248 increased PLA(2) activity in the particulate fraction in a concentration-dependent manner using two radioactive substrates. However, the activity of PLA(2) in the cytosolic fraction decreased. This work also shows that 2,2',4,4',5,5'-hexachlorobiphenyl (HCB) (a di-ortho-substituted nonplanar congener) can increase the activity of PLA(2) in the particulate fraction and decrease the enzyme activity in the cytosolic fraction. The exposure of cell cultures to 3,3',4,4'-tetrachlorobiphenyl (TCB) (a non-ortho-subtituted planar congener) does not alter PLA(2) activity. These results suggest that PCBs, depending on their planar or nonplanar structures, cause a translocation of the enzyme from the cytosol to membranes. To evaluate this possibility, the contents of immunoreactive cPLA(2) were examined by immunoblot analysis in the high-speed supernatant and the particulate fraction of treated cell cultures. The increases/decreases in the amounts of cPLA(2) protein agree with the increases/decreases of PLA(2) activity previously cited. These data demonstrate that the PCB-stimulated redistribution of cPLA(2) to membranes is associated, at least in part, with the changes detected in the activity of the enzyme.     

Modification of cellular fatty acid composition of Hep-G2 cells: effect of antioxidants on cholesterol esterification and secretion

Modification of fatty acid composition of Hep-G2 cells was achieved by 7-9 days of supplementation of culture medium with palmitic, oleic or linoleic acid. Cholesterol release into serum-free culture medium during 24 h of incubation was significantly lower in cells supplemented with linoleic acid, when compared to those supplemented with palmitic, oleic or no additional fatty acid. In cells cultured in the presence of linoleic acid, less [3H]cholesterol was esterified to cholesteryl ester and the mass of cholesteryl ester was significantly lower than in cells cultured with palmitic acid or with no additional fatty acid. The reduction in [3H]cholesterol secretion and the impairment in cholesterol esterification in linoleic acid-treated cells was prevented by addition of butylated hydroxytoluene or probucol concurrently with the fatty acid. The antioxidants also increased esterification and [3H]cholesterol release in cells supplemented with the other fatty acids. It is suggested that cholesterol secretion and esterification are sensitive to peroxidation.     

Different molecular capacity in the induction of apoptosis by polychlorinated biphenyl congeners in rat renal tubular cell cultures

The effects of a commercial polychlorinated biphenyl (PCB) mixture (Aroclor 1248) and two individual PCB congeners were evaluated on rat renal proximal tubule culture cell viability and internucleosomal DNA fragmentation (DNA ladder) characteristic of apoptosis. Treatment with Aroclor 1248 caused the loss of cell viability and promoted apoptosis in a concentration- and time-dependent manner. The two PCB congeners assessed can also induce apoptosis. However, the extent of apoptosis generated was greater for the non-ortho-substituted planar congener (3,3,4,4-tetrachlorobiphenyl) than for the di-ortho-substituted nonplanar congener (2,2,4,4,5,5-hexachlorobiphenyl). This correlated with the loss of cell viability since the planar compound is much more cytotoxic. The results suggest a different molecular mechanism in the induction of apoptosis by planar or nonplanar PCB congeners.     

Evidence for novel mechanisms of polychlorinated biphenyl metabolism in Alcaligenes eutrophus H850

Previous studies indicated that Alcaligenes eutrophus H850 attacks a different spectrum of polychlorinated biphenyl (PCB) congeners than do most PCB-degrading bacteria and that novel mechanisms of PCB degradation might be involved. To delineate this, we have investigated the differences in congener selectivity and metabolite production between H850 and Corynebacterium sp. strain MB1, an organism that apparently degrades PCBs via a 2,3-dioxygenase. H850 exhibited a superior ability to degrade congeners via attack on 2-, 2,4-, 2,5-, or 2,4,5-chlorophenyl rings in PCBs but an inferior ability to degrade congeners via attack on a 4-chlorophenyl ring. Reactivity preferences were also reflected in the products formed from unsymmetrical PCBs; thus MB1 attacked the 2,3-chlorophenyl ring of 2,3,2',5'-tetrachlorobiphenyl to yield 2,5-dichlorobenzoic acid, while H850 attacked the 2,5-chlorophenyl ring to yield 2,3-dichlorobenzoic acid and a novel metabolite, 2',3'-dichloroacetophenone. Furthermore, H850 oxidized 2,4,5,2',4',5'-hexachlorobiphenyl, a congener with no adjacent unsubstituted carbons, to 2',4',5'-trichloroacetophenone. The atypical congener selectivity pattern and novel metabolites produced suggest that A. eutrophus H850 may degrade certain PCB congeners by a new route beginning with attack by some enzyme other than the usual 2,3-dioxygenase.     

Evidence for novel mechanisms of polychlorinated biphenyl metabolism in Alcaligenes eutrophus H850.

Previous studies indicated that Alcaligenes eutrophus H850 attacks a different spectrum of polychlorinated biphenyl (PCB) congeners than do most PCB-degrading bacteria and that novel mechanisms of PCB degradation might be involved. To delineate this, we have investigated the differences in congener selectivity and metabolite production between H850 and Corynebacterium sp. strain MB1, an organism that apparently degrades PCBs via a 2,3-dioxygenase. H850 exhibited a superior ability to degrade congeners via attack on 2-, 2,4-, 2,5-, or 2,4,5-chlorophenyl rings in PCBs but an inferior ability to degrade congeners via attack on a 4-chlorophenyl ring. Reactivity preferences were also reflected in the products formed from unsymmetrical PCBs; thus MB1 attacked the 2,3-chlorophenyl ring of 2,3,2',5'-tetrachlorobiphenyl to yield 2,5-dichlorobenzoic acid, while H850 attacked the 2,5-chlorophenyl ring to yield 2,3-dichlorobenzoic acid and a novel metabolite, 2',3'-dichloroacetophenone. Furthermore, H850 oxidized 2,4,5,2',4',5'-hexachlorobiphenyl, a congener with no adjacent unsubstituted carbons, to 2',4',5'-trichloroacetophenone. The atypical congener selectivity pattern and novel metabolites produced suggest that A. eutrophus H850 may degrade certain PCB congeners by a new route beginning with attack by some enzyme other than the usual 2,3-dioxygenase.     

PCBs in Passaic River Sediments: Some Analytical Considerations

Analytical results for Aroclor may contain a great deal of uncertainty if the relative ratios of certain PCB congeners are substantially altered following differential environmental degradation. Selective degradation of PCB congeners has been shown to occur in biological tissues, and recent studies have shown that Aroclor analyses may significantly underestimate PCB concentrations in fish. The purpose of this study is to assess whether a similar phenomenon can occur with PCB-impacted sediments. Five hundred and thirty-seven sediment samples from the Passaic River were analyzed for Aroclors and selected non-ortho (PCB #77, 126, and 169) and mono-ortho (PCB #105, 114, 118, 123, 156, 157, 167, and 189) coplanar PCB congeners. Aroclors 1248 and 1254 were detected in 67 and 53% of the samples, respectively; 54 samples (approximately 10%) did not contain detectable levels of any Aroclors. In these 54 samples, the sum of the detected PCB congener concentrations was significantly greater, on average, than the Aroclor limit of detection by approximately threefold. In individual samples the sum of the PCB congeners exceeded the Aroclor limit of detection by up to 36-fold. In those samples in which Aroclors were detected, the summed PCB congener concentrations exceeded the Aroclor 1248 and 1254 concentrations, on average, by 41 and 33%, respectively. Given the fact that only a fraction of the 209 PCB congeners were quan-titated, these findings indicate that Arocolor data may significantly underestimate total PCB concentrations in Passaic River sediments. Total PCB data obtained from total homologue analysis indicated that Aroclor results underestimated total PCB mass by up to 43-fold. These findings suggest that caution is required when comparing Aroclor sediment data from the Passaic River to total PCB sediment criteria.     

Degradation of 4,4'-dichlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl, and 2,2',4,4',5,5'-hexachlorobiphenyl by the white rot fungus Phanerochaete chrysosporium.

The white rot fungus Phanerochaete chrysosporium has demonstrated abilities to degrade many xenobiotic chemicals. In this study, the degradation of three model polychlorinated biphenyl (PCB) congeners (4,4'-dichlorobiphenyl [DCB], 3,3',4,4'-tetrachlorobiphenyl, and 2,2',4,4',5,5'-hexachlorobiphenyl) by P. chrysosporium in liquid culture was examined. After 28 days of incubation, 14C partitioning analysis indicated extensive degradation of DCB, including 11% mineralization. In contrast, there was negligible mineralization of the tetrachloro- or hexachlorobiphenyl and little evidence for any significant metabolism. With all of the model PCBs, a large fraction of the 14C was determined to be biomass bound. Results from a time course study done with 4,4'-[14C]DCB to examine 14C partitioning dynamics indicated that the biomass-bound 14C was likely attributable to nonspecific adsorption of the PCBs to the fungal hyphae. In a subsequent isotope trapping experiment, 4-chlorobenzoic acid and 4-chlorobenzyl alcohol were identified as metabolites produced from 4,4'-[14C]DCB. To the best of our knowledge, this the first report describing intermediates formed by P. chrysosporium during PCB degradation. Results from these experiments suggested similarities between P. chrysosporium and bacterial systems in terms of effects of congener chlorination degree and pattern on PCB metabolism and intermediates characteristic of the PCB degradation process.     

An enzyme based dechlorination of a polychlorinated biphenyl (PCB) mixture,Aroclor 1248, using glutathione S-transferases from the northern quahog Mercenaria mercenaria

The glutathione S-transferases from the northern quahog (Mercenaria mercenaria) from control and contaminated sites were subjected to incubation with polychlorinated biphenyls in an Aroclor 1248 mixture. Subsequent solvent-solvent extraction and gas chromatographic analysis revealed that 2 of the 28 congeners present in the Aroclor 1248 mixture were affected by the presence of the GST. The first of the aforementioned congeners with a retention time of 36.7 min by gas chromatographic analysis decreased in total content. The largest decrease in the 36.7 min peak was the result of incubation with GSTs purified from quahogs taken from the Superfund site in New Bedford Harbor, New Bedford, MA. The second of the affected congeners with a retention time of 59 min showed an increase, which could result from the glutathione conjugation to the PCB congener. The Aroclor 1248 mixture (a limited number of its constituent congeners) also acts as a competitive inhibitor of the GST activity, which is indicative of a substance interacting with the free GST in solution. The ultimate result of the conjugation of the PCB congener to GSH would be the formation of a hydrophillic conjugate of an otherwise insoluble PCB. The PCB-GSH conjugating activity of the quahog GSTs may ultimately serve as a tool for PCB remediation.     

Rapid assay for screening and characterizing microorganisms for the ability to degrade polychlorinated biphenyls

We designed a rapid assay that assesses the polychlorinated biphenyl (PCB)-degradative competence and congener specificity of aerobic microorganisms, identifies strains capable of degrading highly chlorinated biphenyls, and distinguishes among those that degrade PCBs by alternative pathways. Prior attempts to assay PCB-degradative competence by measuring disappearance of Aroclors (commercial PCB mixtures) have frequently produced false-positive findings because of volatilization, adsorption, or absorption losses. Furthermore, these assays have generally left the chemical nature of the competence obscure because of incomplete gas chromatographic resolution and uncertain identification of Aroclor peaks. We avoided these problems by using defined mixtures of PCB congeners and by adopting incubation and extraction methods that prevent physical loss of PCBs. Our assay mixtures include PCB congeners ranging from dichloro- to hexachlorobiphenyls and representing various structural classes, e.g., congeners chlorinated on a single ring (2,3-dichlorobiphenyl), blocked at 2,3 sites (2,5,2'5'-tetrachlorobiphenyl), blocked at 3,4 sites (4,4'-dichlorobiphenyl), and lacking adjacent unchlorinated sites (2,4,5,2',4',5'-hexachlorobiphenyl). The PCB-degrative ability of microorganisms is assessed by packed-column gas chromatographic analysis of these defined congener mixtures following 24-h incubation with resting cells. When tested with 25 environmental isolates, this assay revealed a broad range of PCB-degradative competence, highlighted differences in congener specificity and in the extent of degradation of individual congeners, predicted degradative competence on commercial PCBs, and (iv) identified strains with superior PCB-degradative ability.     

The synthesis and secretion of gastric mucus glycoprotein by mucosal cells cultured in the presence of ethanol

The effect of ethanol on the synthesis and secretion of mucus glycoprotein in gastric mucosal cells was investigated. The mucosal cell suspensions were subjected to a short-term (4 h) culture in the presence of 0-1.5 M ethanol, with [3H]proline and [3H]palmitic acid as markers for glycoprotein synthesis and acylation. The synthesized labeled mucus glycoprotein was isolated from the incubation medium (extracellular glycoprotein) and from the mucosal cells (intracellular glycoprotein), and analyzed. Depending upon the ethanol concentration in the cell culture medium, two distinct effects on the synthesis and secretion of mucus glycoprotein were observed. The cells cultured in the presence of 0.02-0.1 M ethanol showed increased ability for the incorporation of [3H]proline and [3H]palmitic acid, and for the secretion of the newly assembled mucus glycoprotein. The synthesis of the glycoprotein increased 18-fold, acylation 5-fold, and secretion 10-fold. The synthesized glycoprotein, however, contained four to five times less of acyl-bound fatty acids. Ethanol at 0.1-1.5 M caused a marked reduction (62-64%) in the mucus glycoprotein synthesis, but the amount of glycoprotein released to the medium remained constant. This indicated that higher concentrations of ethanol caused the release of the preformed intracellular mucus glycoprotein reserves. The results demonstrate that gastric mucosal cells incubated in the presence of ethanol exhibit impaired synthesis and secretion of mucus glycoprotein, and that the severity of impairment depends upon the ethanol concentration.     

Biotransformation of PCBs in Contaminated Sludge: Potential for Novel Biological Technologies

In this study, the biological transformation of polychlorinated biphenyls (PCBs) was investigated in sludge from the Ralston Street Lagoon (RSL), a United States Environmental Protection Agency (USEPA) designated Toxic Substances Control Act (TSCA) site, in Gary, IN. A biological tilled soil reactor (BTSR) operating under cycling anaerobic‐aerobic conditions and vermicomposting bioreactors (VBs) inoculated with Eisenia foetida earthworms were both systematically investigated. Sludge heavily contaminated with PCBs (> 500 ppm PCB as Aroclor 1248) was loaded into the BTSRs and amended sequentially with PCB‐dechlorinating anaerobic sediments and then aerobic PCB biodegrading microbes. The VBs were loaded with sludge mixed in varying ratios with sterile soil and then inoculated with earthworms. Bioreactors were monitored for the duration of the studies (ranging from four to nine months) and samples were regularly removed, extracted and analyzed for PCB congener content. Appropriate biotic and negative abiotic controls were maintained under the various conditions to quantify and measure the biological transformation of the PCB's. All samples were analyzed for PCB congener concentrations by Soxhlet extraction followed by gas chromatography with electron capture detection (ECD). In the BTSRs loaded initially with 500 ppm of PCBs, a 75 % reduction of total PCB was obtained while the BTSR loaded with 140 ppm PCBs revealed only a 25 % reduction in total PCB level. Sample analyses from the VBs demonstrated total PCB reductions ranging from 55 to 66 %, although worm‐free control reactors showed PCB attenuations from 48 to 68 %. Analysis of earthworms showed an increase in PCB levels in the earthworm biomass, with concentrations reaching as high as 313 ppm. Mass balance analysis of the VB results demonstrated that most of the PCBs were bioaccumulated, although some PCB elimination was demonstrated. The results from both the anaerobic‐aerobic cycling BTSR and VB investigations demonstrate potential for application for site clean‐up and possible bioremediation of the Ralston Street Lagoon sludge.     

Molecular species analysis of 1,2-diacylglycerol released in response to progesterone binding to the amphibian oocyte plasma membrane

Progesterone, the physiological inducer of amphibian meiosis, acts within minutes at plasma membrane receptors of the Rana pipiens oocyte to release 1,2-diacylglycerol (DAG) from plasma and intracellular membranes. High-performance liquid chromatography (HPLC) analysis of lipid extracts of uninduced oocytes indicates the presence of at least three classes of DAG with a total DAG content of about 150 micromol/kg wet weight. Within 3-5 min after exposure to progesterone, there was a differential increase in all three DAG classes with a twofold increase in total DAG by 10 min. The fatty acid composition of the DAGs in uninduced and progesterone-stimulated oocytes was compared using thin layer chromatographic analysis of lipid extracts from oocytes double-labeled with [14C] or [3H]glycerol and [14C] or [3H]fatty acids. The ratio of labeled fatty acid/labeled glycerol was measured in phosphatidylcholine (PC), phosphatidylinositol (PI) and DAG. The linoleic (18:2) or arachidonic (20:4) acid/glycerol ratios in basal DAG were low compared to that in PC or PI. In contrast, the myristic (14:0), palmitic (16:0) or oleic (18:1) acid/glycerol ratios in basal DAG were relatively high compared to the ratio in PC and PI. A transient increase in both linoleic and palmitic acid labeling of DAG occurred within the first 1-2 min in progesterone-treated oocytes, followed by a return to or below the basal level. Arachidonic and myristic acid labeling of DAG fall within the first minute after progesterone treatment, followed by a sustained rise over the next 10 min. The [3H]oleic acid/[14C]glycerol ratio of DAG does not change significantly following exposure to progesterone. Pretreatment with a phospholipid N-methylation inhibitor (2-methylaminoethane) precluded the rise in linoleic and palmitic acid-rich DAG, whereas pretreatment with a diglyceride kinase inhibitor (D102) produced a sustained elevation of linoleic and palmitic acid-rich DAG. These results indicate that the DAG released in response to progesterone is composed of multiple new molecular species of DAG and that both the palmitate and linolate-rich forms are rapidly phosphorylated to form phosphatidic acid (PA). The newly formed DAG species differ from the basal DAG species and reflect sequential activation of sphingomyelin (SM) synthase, PC-specific phospholipase D (PLD) and PI-specific phospholipase C in response to progesterone, which we have described previously.     

In vitro acylation of rat gastric mucus glycoprotein with [3H]palmitic acid

The incorporation of fatty acids into gastric mucus glycoproteins was studied by incubating rat gastric mucosal cell suspensions with [9,10-3H]palmitic acid and [3H]proline. The mucus glycoprotein polymer, secreted into the growth medium (extracellular) and that contained within the cells (intracellular), was purified from the other components of the secretion, thoroughly delipidated, and then analyzed for the radiolabeled tracers. Both pools of mucus glycoprotein, incubated in the presence of [3H]palmitic acid, contained radioactive label which could not be removed by gel filtration, CsCl density gradient centrifugation, sodium dodecyl sulfate-gel electrophoresis, or lipid extraction. Treatment of the purified mucus glycoprotein with 1 M hydroxylamine or 0.3 M methanolic KOH released the radioactivity, thus indicating that [3H]palmitic acid was covalently bound by ester linkage to the glycoprotein. The released radioactivity was associated mainly (87%) with palmitic acid. The incorporation ratio of [3H]proline to [3H]palmitic acid was 0.12:1.0 in the extracellular glycoprotein and 1.38:1.0 in the intracellular glycoprotein, which suggested that acylation of mucus glycoprotein occurs in the intracellular compartment after completion of its polypeptide core. The fact that incorporation of [3H]palmitic acid was greater in the glycoprotein subunits than in the glycoprotein polymer indicates that acylation takes place near the end of subunit processing but before their assembly into the high molecular weight mucus glycoprotein polymer.     

Extensive degradation of Aroclors and environmentally transformed polychlorinated biphenyls by Alcaligenes eutrophus H850

We have isolated and characterized a strain of Alcaligenes eurtrophus, designated H850, that rapidly degrades a broad and unusual spectrum of polychlorinated biphenyls (PCBs) including many tetra- and pentachlorobiphenyls and several hexachlorobiphenyls. This strain, which was isolated from PCB-containing dredge spoils by enrichment on biphenyl, grows well on biphenyl and 2-chlorobiphenyl but poorly on 3- and 4-chlorobiphenyl. Capillary gas-chromatographic analysis showed that biphenyl-grown resting cells of H850 degraded the components of 38 of the 41 largest peaks of Aroclor 1242 and 15 of the 44 largest peaks of Aroclor 1254, resulting in an overall reduction of PCBs by 81% for Aroclor 1242 (10 ppm) and 35% for Aroclor 1254 (10 ppm) in 2 days. Furthermore, H850 metabolized the predominantly ortho-substituted PCB congeners that resulted from the environmental transformation of the more highly chlorinated congeners of Aroclor 1242 by the upper Hudson River anaerobic meta-, para-dechlorination agent system C (J. F. Brown, R. E. Wagner, Jr., D. L. Bedard, M. J. Brennan, J. C. Carnahan, R. J. May, and J. J. Tofflemire, Northeast Environ. Sci. 3:167-179, 1984). The congener selectivity patterns indicate that a two-step process consisting of anaerobic dechlorination followed by oxidation by H850 can effectively degrade all of the congeners in Aroclor 1242 and possibly all those in Aroclor 1254.     

Extensive degradation of Aroclors and environmentally transformed polychlorinated biphenyls by Alcaligenes eutrophus H850.

We have isolated and characterized a strain of Alcaligenes eurtrophus, designated H850, that rapidly degrades a broad and unusual spectrum of polychlorinated biphenyls (PCBs) including many tetra- and pentachlorobiphenyls and several hexachlorobiphenyls. This strain, which was isolated from PCB-containing dredge spoils by enrichment on biphenyl, grows well on biphenyl and 2-chlorobiphenyl but poorly on 3- and 4-chlorobiphenyl. Capillary gas-chromatographic analysis showed that biphenyl-grown resting cells of H850 degraded the components of 38 of the 41 largest peaks of Aroclor 1242 and 15 of the 44 largest peaks of Aroclor 1254, resulting in an overall reduction of PCBs by 81% for Aroclor 1242 (10 ppm) and 35% for Aroclor 1254 (10 ppm) in 2 days. Furthermore, H850 metabolized the predominantly ortho-substituted PCB congeners that resulted from the environmental transformation of the more highly chlorinated congeners of Aroclor 1242 by the upper Hudson River anaerobic meta-, para-dechlorination agent system C (J. F. Brown, R. E. Wagner, Jr., D. L. Bedard, M. J. Brennan, J. C. Carnahan, R. J. May, and J. J. Tofflemire, Northeast Environ. Sci. 3:167-179, 1984). The congener selectivity patterns indicate that a two-step process consisting of anaerobic dechlorination followed by oxidation by H850 can effectively degrade all of the congeners in Aroclor 1242 and possibly all those in Aroclor 1254.     

Myristic acid utilization in Chinese hamster ovary cells and peroxisome-deficient mutants.

Chinese hamster ovary (CHO) cells convert [9,10-3H]myristic acid ([3H]14:0) to several lipid-soluble, radioactive metabolites that are released into the medium. The main products are lauric (12:0) and decanoic (10:0) acids. Some of the 12:0 formed also is retained in cell lipids. Similar metabolites are not synthesized from palmitic (16:0), oleic (18:1), or arachidonic (20:4) acids, and the addition of these fatty acids does not reduce the conversion of [3H]14:0 to 12:0. Two peroxisome-deficient CHO cell lines do not convert [3H] 14:0 to any polar metabolites, but, they elongate, desaturate, and incorporate [3H]14:0 into intracellular lipids and proteins normally. While BC3H1 muscle cells convert some [3H]14:0 to 12:0, they also produce at least nine lipid-soluble polar products from [3H]12:0. These findings suggest that a previously unrecognized function of myristic acid is to serve as a substrate for the synthesis of 12:0, which can be either secreted into the medium or converted to other oxidized metabolites. The absence of this peroxisomal oxidation pathway, however, does not interfere with other aspects of myristic acid metabolism, including protein myristoylation.     

Low surfactant concentration increases fungal mineralization of a polychlorinated biphenyl congener but has no effect on overall metabolism

Three white rot fungi were compared for their ability to attack polychlorinated biphenyl (PCB) congeners in the presence and absence of the non-ionic Triton X-100 or the anionic Dowfax 8390 surfactants at half their critical micelle concentrations. Neither surfactant affected PCB biodegradation monitored by gas chromatography but the release of 14CO2 from 2,4',5-[U-14C]trichlorobiphenyl by Trametes versicolor was stimulated 12% by Triton X-100. Since mineralization is the complete metabolism of the congener and biodegradation was measured as substrate disappearance, Triton X-100 is proposed to aid intracellular solubilization of 2,4',5-trichlorobiphenyl for complete oxidation by T. versicolor.     

Low-temperature-induced changes in intracellular fatty acid fluxes in Dunaliella salina

Two-minute exposures to exogenous [14C]palmitic, [14C]oleic, or [14C]lauric acid differentially labeled the lipids of Dunaliella salina microsomes and chloroplasts. Changes in fatty acid desaturation and intracellular movement during a subsequent 16-h incubation in nonradioactive medium indicated a slow transfer of lipids into the chloroplast from other organelles. Since Dunaliella lacks the massive traffic of microsomally produced glycerolipids into chloroplast galactolipids that dominates chloroplast-microsome lipid relations in most plant cells, it affords a sensitive system for studying more subtle intracellular lipid fluxes. Lowering the culture temperature from 30 to 12 degrees C was more inhibitory toward glycerolipid biosynthesis in chloroplasts than in microsomes. The ability of Dunaliella chloroplasts to utilize microsomal lipids may be essential for their systematic acclimation to low temperature.     

A Preliminary Laboratory Investigation of PCB Flux from Dredge Resuspensions and Residuals

A preliminary laboratory investigation was conducted to understand the relative contributions of major dredge resuspension and residual processes on the releases of polychlorinated biphenyl (PCB) contaminants from sediments to water column. Sediments from New Bedford Harbor were used as test samples. Six sets of experiments were run for simulated resuspension and residual scenarios. During the experiments, water above the sediments was recirculated by peristaltic pumping or orbital shaking and the levels of two PCBs, Aroclor 1248 (PCB-1248) and Aroclor 1254 (PCB-1254), were monitored for 15 days. Analysis of the model predicted data indicated that resulting water column PCB concentrations differed with sediment surface, residual, and resuspension type. Highest PCB water column concentrations were observed for a condition which used a settled fluff from thin sediment slurry as a residual source and the column water was recirculated by orbital shaking. Lowest water column PCB levels were observed for a thick sediment deposit placed over clean sand. The PCB levels in the water column for all six simulated conditions were several orders higher than the USEPA ambient water quality criteria concentrations for aquatic environment and human consumption.