Structure and metabolism of phospholipids in bovine epididymal spermatozoa.

Lipid analysis of bovine epididymal spermatozoa showed relatively large amounts of alkylacyl- and alk-1-enylacylglycerols in their choline and ethanol-amine phospholipids and alkylacylglycerol as the major constituent of a glycolipid tentatively identified as a monogalactosyl sulfate. The ether lipids exhibited remarkably simple molecular structures, i.e., the phospholipids had only 16:0 as alkyl and alk-1-enyl groups and their constituent fatty acids were almost exclusively 22:5 (n-6) and 22:6 (n-3). The glycolipid had mainly 16:0 as both alkyl and acyl moieties. In contrast, the diacyl choline and ethanolamine phosphoglycerides exhibited a much more complex fatty acid composition. 1,2-Diacylglycerols were the major nonpolar glycerolipid class and their acyl groups consisted almost exclusively of 14:0, 16:0 and 18:0. Labeled glycerol and dihydroxyacetone added to the incubation medium were readily incorporated into sperm lipids under both aerobic and anaerobic conditions. In each case, diacylcholine phosphoglycerides, diacylglycerols and phosphatidic acid were the major labeled lipids. Distribution of label among the molecular species of diacylglycerols and choline phosphoglycerides resembled somewhat their natural abundance. No radioactivity was found in alkylacyl or alk-1-enylacyl glycerolipids. The ether lipids may provide stable structural components of sperm membrane while the diacyl analogs undergo degradation and resynthesis.

Alterations in the synthesis of proteins in hepatocytes of rainbow trout fed cyclopropenoid fatty acids.

Hepatocytes from rainbow trout reared on a diet containing cyclopropenoid fatty acids were analyzed for alterations in protein composition and synthesis by double label experiments. Both cytosolic and microsomal hepatocyte fractions were investigated. In the cytosolic fraction, the synthesis of proteins in the range of 68,000 to 74,000 daltons were significantly decreased. The identity of these proteins remains uncertain. A pronounced depression in both the mass and apparent synthesis of a 200,000 to 240,000 dalton microsomal protein was also observed. Immunoblotting with antibodies raised against goose acetyl-CoA carboxylase and avidin-peroxidase staining suggest that this protein is acetyl-CoA carboxylase. Moreover, synthesis of this protein as well as mass of the protein in cyclopropenoid fatty acid-fed fish were less than 20% of that found in control fish.

Isolated brain capillary endothelia: influence of various levels of essential fatty acids on the acyl group composition of glycerophospholipids.

On day seven of gestation. Wistar rats were assigned to a high essential fatty acid (EFA), low EFA, or a fat free diet. The same diets were continued during lactation. On weaning, the offspring were fed the same diets as their mother. Rats were killed at 222 days, brain capillary endothelia isolated, and total lipids extracted from the purified capillaries. The composition of the constituent fatty acids of ethanolamine glycerophospholipid (EGP), choline glycerophospholipid (CGP), and the alk-1-enyl EGP composition from each diet is reported. A decrease in dietary EFA led to reduced proportions of total saturated acyl groups in EGP with no change observed in the total saturated acyl groups from CGP, and an increase in monoenoic fatty acids, particularly 18:1n-9 for each phospholipid class. The proportions of 20:4n-6 in alk-1-enyl EGP were reduced in fat-free fed animals. In addition, the relationship between 20:3n-9 and 20:4n-6 fatty acids in brain capillary endothelia were markedly increased with a reduction in dietary fat. Low EFA and fat deficient animals showed a tendency to sequester 22:6n-3.

Lipid and fatty acyl composition of rat brain capillary endothelia isolated by a new technique.

A method is described for the isolation of pure capillary endothelia from rat brain and the phosphlipid composition of these cells is reported. This method is rapid and requires only a small amount of starting material. It involves: (a) tissue disruption by high speed homogenization, (b) separation of the capillary endothelia from other brain structures using sucrose gradients, and (c) a final purification using a glass bead column. Choline and ethanolamine phosphoglycerides were found to be the predominant lipid classes of these cells amounting to 31.9% and 24.4%, respectively, of total phospholipids. The choline phosphoglycerides consisted almost exclusively of 1,2-diacyl glycerophosphorylcholine, whereas the ethanolamine phosphoglycerides consisted of approximately equal amounts of 1,2-diacyl and 1-alk-1'-enyl-2-acyl glycerophosphorylethanolamine. The composition of the constituent fatty acids of both choline and ethanolamine phosphoglycerides and the alk-1-enyl composition of ethanolamine phosphoglycerides is reported. Saturated fatty acids accounted for 45% of the total fatty acids in choline phosphoglycerides and for 53% in ethanolamine phosphoglycerides. Arachidonic acid accounted for approximately 48% of the total fatty acids in alk-1-enyl ethanolamine phosphoglyceride.

Alterations of hepatic acetyl-CoA carboxylase by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on acetyl-CoA carboxylase (ACC) activity and synthesis was examined. Male Wistar rats received a single i.p. injection of TCDD (53 micrograms/kg), and nine days later body weight, liver weight, hepatic lipid, ACC activity and mass were determined and compared to pair-fed controls. Body weights of TCDD-treated animals decreased, while liver weights increased resulting in an increase in liver to body weight ratios. ACC activity was decreased by 65%, however sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western analysis using a biotin specific probe revealed that ACC protein levels were not appreciably changed. In addition, there was a large increase in exogenous lipid material in TCDD-treated livers as determined by osmium tetroxide staining. These data suggest that the decrease in ACC activity may be due to direct inhibition of the enzyme by negative allosteric interactions with free fatty acids released from adipose tissue that subsequently accumulate in liver.

Isolation and identification of acetyl-CoA carboxylase from rainbow trout (Salmo gairdneri) liver.

Acetyl-CoA carboxylase is the pivotal enzyme in the de novo synthesis of fatty acids and is the only carboxylase with a biotin-containing subunit greater than 200,000 daltons. The biotin moiety is covalently linked to the active site and has a high affinity (Kd = 10(-15) M) for the protein avidin. This relationship has been used in previous studies to identify acetyl-CoA carboxylase isolated from mammalian species. However, acetyl-CoA carboxylase has not been isolated and characterized in a poikilothermic species such as the rainbow trout. The present study describes the isolation and identification of acetyl-CoA carboxylase in the cytosol of rainbow trout (Salmo gairdneri) liver. The enzyme was isolated using two distinct procedures--polyethylene glycol precipitation and avidin-Sepharose affinity chromatography. Identification of the isolated protein as acetyl-CoA carboxylase was made by the following: (1) sodium dodecyl sulfate-polyacrylamide gel electrophoresis; (2) avidin binding; (3) in vivo labeling with [14C]biotin; and (4) acetyl-CoA carboxylase-specific activity. The subunit molecular weight of the major protein was 230,000 daltons +/- 3.3%. This protein was shown to bind avidin (Mr = 16,600) prior to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating the presence of biotin. In addition, protein isolated from fish that had previously received intraperitoneal injections of [14C]biotin, showed the majority of radioactivity associated with the 230,000 dalton protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Turnover of label from [1-14C]linolenic acid in phospholipids of coho salmon, Oncorhynchus kisutch.

Juvenile coho salmon were injected intraperitoneally with [1-14C] linolenic acid and sampled at 24, 120, and 240 hr. Liver, heart and gill lipids were extracted analyzed, and halflives of individual liver glycerophospholipids and n-3 fatty acids determined from rates of loss of radioactivity. Incorporation of label into gill was much less than into either heart or liver. Total acyl halflife was shorter for the choline phospholipids than for the ethanolamine phospholipids, as were the halflives of all individual n-3 fatty acids. Eicosapentaenoic acid (20:5n-3) had the shortest halflife in both phospholipids (50-60 hr), while docosapentaenoic acid (22:5n-3) and docosahexaenoic acid (22:6n-3) had much longer halflives. Specific activities of the shorter chain n-3 fatty acids were much greater than the longer, more unsaturated homologs at all times, suggesting possible differences in their mechanisms of incorporation into phospholipids. Diacylglycerol analysis indicated that de novo synthesis could be responsible for the incorporation of only a small portion of the labeled long chain fatty acids found in phospholipids. The fatty acid halflives reported here for salmon are in general agreement with those found previously in mammals.

Alteration of liver microsomal proteins from rainbow trout (Salmo gairdneri) fed cyclopropenoid fatty acids.

Rainbow trout were fed diets containing cyclopropenoid fatty acids (CPFA) at 50 and 300 ppm with appropriate controls fed CPFA-free diets. Treatment with CPFA altered the overall microsomal protein composition in a manner suggesting a reduction of high molecular weight components. One protein found in low concentration in controls appeared dominant in experimental animals, with the effect more pronounced as dietary levels of CPFA increased. The estimated molecular weight of this component was 41,500 daltons. Membrane fractions from CPFA-fed fish separated on a Bio-Gel P-150 column revealed a significant number of small molecular weight components that suggest degradation of microsomal proteins. These data suggest an alteration by CPFA of membrane protein composition.

Fat deficiency in rats during development of the central nervous system and susceptibility to experimental allergic encephalomyelitis.

On day 14 of gestation, Sprague-Dawley rats were assigned to a diet adequate in fat (C), a fat-deficient diet (FD), or a fat-deficient diet supplemented with ethyl linoleate (FD-S). The same diets were continued during lactation. On weaning, the offspring were fed the same diets as their mothers. Rats were killed at 21 and 33 days, and the lipid compositions of brain, brain myelin, and spinal cord myelin were determined. Experimental allergic encephalomyelitis (EAE) was induced in animals from each group at 54 days of age. Acute EAE occurred after 13 days, and on day 14 (day 68 of age), the rats were killed. Body, brain, and brain myelin developments were slower in the FD and FD-S rats during early life. At 68 days, brain myelin from all groups reached mature composition, although body and brain weights of FD and FD-S rats remained lower than those of controls. With the exception of a slightly lower plasmalogen content at 33 and 68 days, the composition of spinal cord myelin from FD and FD-S rats was similar to that of C rats throughout the period of study. The plasmalogen content at 33 and 68 days, the composition of spinal cord myelin from FD and FD-S rats was similar to that of EAE occurred in animals from the FD group. The incidence of the disease in FD-S rats was similar to that in the controls. A reduction in total brain protein occurred in FD-EAE rats and in C-EAE and FD-EAE cerebrosides. Myelin from brain and spinal cord of EAE rats did not differ appreciably in protein content or lipid composition from myelin of controls. It was concluded that fat deficiency during development leads to increased susceptibility to EAE, and that a supplement of a source of linoleic acid has a marked protective effect against EAE.

The use of a zwitterionic detergent in two-dimensional gel electrophoresis of trout liver microsomes.

CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-Propane sulfonate, a zwitterionic detergent, has been shown to exhibit superior membrane protein solubilizing characteristics as compared to nonionic detergents. Replacement of NP-40 with CHAPS in isoelectric focusing of rainbow trout liver microsomes has increased resolution markedly. The two-dimensional electrophoretic system described will allow effective resolution of up to 300 micrograms of crude microsomal protein. CHAPS exhibits no effect on the stability or type of pH gradient when compared to NP-40 during isoelectric focusing in the presence of urea.

The effect of high-protein and high-carbohydrate diets on [125I]iodoinsulin binding in skeletal muscle plasma membranes and isolated hepatocytes of rainbow trout (Salmo gairdneri).

[125I]iodoinsulin-binding studies in the presence of a concentration range of bovine insulin were conducted to establish specific insulin-binding levels in skeletal muscle plasma membranes and isolated hepatocytes of rainbow trout (Salmo gairdneri) reared on control, high-protein or high-carbohydrate diets. Negative co-operativity was observed and receptor concentrations and apparent dissociation constants established for each preparation. No differences of specific binding attributed to diet were detected in skeletal muscle plasma membrane preparations; however, the receptor concentration of isolated hepatocytes from high-carbohydrate-reared trout was increased. This contrasted to comparable mammalian studies.

B-naphthoflavone induction and its effect on hepatic phospholipid metabolism in rainbow trout (Salmo gairdneri).

1. B-naphthoflavone (BNF) induction of microsomal cytochrome P-488 and its effect on liver phospholipid metabolism were examined in rainbow trout (Salmo gairdneri) 24 and 96 hr after intraperitoneal injection. 2. Cytochrome P-448 content increased at 96 hr to approximately double the cytochrome content of control fish. 3. Computer-analyzed laser densitometry scans of LDS-polyacrylamide gels of 96 hr BNF-treated liver microsomes showed a 90% increase in cytochrome P-448 levels. 4. A 34% increase in microsomal phospholipid (mumol/mg protein) was observed 24 hr after BNF injection, with a marked increase in choline, ethanolamine and inositol phospholipids. 5. Following 96 hr of exposure to BNF some differences in enzyme activity were noted; choline kinase and cytidylyltransferase activities were reduced, while a marked increase was observed in choline phosphotransferase activity. In light of current information on induction of liver microsomal phospholipid metabolism in mammals, the results of the this study suggest that trout do not respond like mammals to inducers of monooxygenase activity.

Characterization of plasma membrane lipids and luteinizing hormone receptors of ovine corpora lutea during luteolysis and early pregnancy.

Lipid composition of plasma membranes from luteal cells was examined to determine whether changes in this organelle occur during regression and maintenance of the corpus luteum in nonpregnant (NP) and pregnant (P) ewes, respectively. Forty ewes were assigned to be killed on Day 13 or 15 of the estrous cycle (D13-NP and D15-NP) or pregnancy (D13-P and D15-P). Purification of luteal plasma membranes on discontinuous sucrose gradients yielded two fractions, designated F1 and F2, that exhibited the greatest enrichment of 5'-nucleotidase activity (five- and fourfold, respectively) over that of the homogenate. These fractions also yielded the lowest contamination by endoplasmic reticulum as represented by nicotinamide adenine dinucleotide phosphate (NADPH) cytochrome C reductase activity and mitochondrial membranes as indicated by succinate dehydrogenase activity. Predominant phospholipids identified in membranes obtained from all groups were phosphatidylcholine (PC, 48.9 +/- 0.6% of total phospholipid), phosphatidylethanolamine (PE, 33.3 +/- 0.4%), sphingomyelin (SPH, 9.7 +/- 0.3%), phosphatidylserine (PS, 3.5 +/- 0.2%), and phosphatidylinositol (PI, 4.0 +/- 0.5%). No changes in microgram phospholipid/mg membrane protein were observed for any luteal phospholipid on D13 and 15 of the estrous cycle or pregnancy. No significant changes in the relative percentages of major fatty acids present in PC (palmitic [16:0], oleic [18:1]), PE (stearic [18:0], 18:1 and arachidonic [20:4]), or PS (18:0, 18:1, docosatetraenoic [22:4]), nor in the ratios of unsaturated (U) to saturated (S) fatty acids in these phospholipids were observed. Significant differences in unsaturated fatty acids of chain length greater than 20 carbons present in minor quantities in PC, PE, and PS were detected between NP and P ewes as well as between days within reproductive stage. The profile of major fatty acids present in PI revealed decreases in 18:0 and 20:4 in D15-NP and increases in 22:4 and docosapentaenoic acid (22:5) in luteal membranes of both D13- and D15-NP ewes relative to the levels of these fatty acids in PI of corresponding groups of pregnant ewes. There was a general trend for 20:4 levels of PC and PI in membranes of D15-NP ewes to be inversely related to those of D15-P ewes. Collectively, these changes were reflected by an increased U:S fatty acid ratio in luteal membrane PI during the estrous cycle. Specific binding of [125I] iodo-human chorionic gonadotropin to luteal plasma membranes from NP and P ewes on D13 and 15 (6/group) revealed similar affinities and concentrations of unoccupied luteinizing hormone (LH) receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Acyl and alkenyl group composition of brain subcellular fractions of goldfish (Carassius auratus L.) acclimated to different environmental temperatures.

Goldfish were acclimated to 5, 15, and 30°C, and the acyl group composition of choline phosphoglycerides (CPG) and ethanolamine phosphoglycerides (EPG) from whole brain and brain subcellular particles was examined. With the exception of synaptosomal CPG, the acyl group composition of CPG from whole brain and subcellular particles, including myelin, from cold-acclimated fish showed little response to the change in environmental temperature. Those changes that did occur were consistent with the expected trend toward a higher degree of unsaturation of the CPG acyl groups in fish acclimated to 5°C. The acyl group composition of CPG from synaptosomes of the cold-acclimated fish did, however, differ markedly in having a reduced unsaturation index (U.I.) and unsaturated: saturated fatty acid ratio (UFA:SFA) which was caused mainly by the decrease in 22∶6n-3 content. In contrast, changes in the acyl group composition of EPG on cold acclimation were greater than those observed in any CPG fraction. The generally expected trend toward greater unsaturation was observed only in mitochondrial and myelin EPG. Moreover, in all fractions the amount of 22∶6n-3 in EPG was lower at decreased environmental temperatures. In the synaptosomal and microsomal EPG, the reduction in 22∶6n-3 was such that a markedly reduced U.I. was obtained. It is suggested that two compensatory mechanisms maintain the necessary degree of membrane permeability and fluidity in order to prevent transition to a crystalline state at lower temperatures.

Aflatoxin B1 metabolism and DNA binding in isolated hepatocytes from rainbow trout (Salmo gairdneri).

The metabolism of aflatoxin B1 (AFB1) was examined in freshly isolated hepatocytes from rainbow trout. Intracellular DNA adduct formation was linearly related to AFB1 dose, and qualitatively similar to adducts formed in vivo. The rate of adduct accumulation was constant during the first hour following completion of the preparation, after which an increase and gradual decrease in rate routinely occurred. The relative rates of production of the major unbound AFB1 metabolites aflatoxicol, aflatoxin M1, and polar conjugates, also remained constant over the first hour of preparation age, but subsequently changed in a manner consistent with the changes in DNA binding. The common solvent vehicles ethanol and dimethyl sulfoxide were shown to seriously perturb AFB1 metabolism and DNA binding even at levels less than 1%. A simple method is reported for removal of ethanol prior to introduction of hepatocytes for incubation with AFB1. The influence of cell concentration was also examined. DNA binding and relative distribution of AFB1 metabolites showed little or no dependence in the range 1-6 x 10(6) cell/ml, but were substantially altered above 10(7) cells/ml. Under defined conditions, studies in isolated hepatocytes appear to reflect in vivo cell capabilities for AFB1 metabolism.

Ah receptor involvement in mediation of pyruvate carboxylase levels and activity in mice given 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The arylhydrocarbon receptor (AhR) plays a central role in mediating 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity in animals. The investigations described here provide evidence that support a role for the AhR in TCDD-mediated pyruvate carboxylase (PC) level/activity reductions in mice. Pyruvate carboxylase plays a pivotal role in gluconeogenesis and in supplying carbon units for the citric acid cycle. Delivered ip in a corn oil carrier, TCDD suppresses PC activity/amount at doses as low as 1 microgram/kg in responsive C57BL/6J(Ahb/b) mice. Corn oil alone injected ip into mice at 4 mL/kg appears to be an inducer that increases the amount and activity of PC. However, TCDD suppresses this induction. In the Ahb/b mouse, PC levels and activity are reduced to 10% of control values at a dose of 75 micrograms/kg. A time-course experiment shows that the PC reductions are apparent within 16 hours post-TCDD exposure. Here we report investigations on the PC/TCDD response using a congenic C57BL/6J(Ahd/d) mouse strain having an AhR with a low affinity for TCDD. If the PC/TCDD response is AhR mediated, the congenic mouse strain (Ahd/d) would require much higher doses of TCDD to suppress PC. In the Ahd/d mice, we observe that an approximately 60-fold increase in TCDD dose is necessary to produce a PC/TCDD effect. We also find that in Ahd/d mice, corn oil does not induce an increase in PC activity/amounts, as reported for Ahb/b mice.

Alterations in hepatic microsomal protein levels in rainbow trout fed cyclopropenoid fatty acids analyzed by two-dimensional gel electrophoresis.

Two-dimensional gel electrophoresis was used to analyze the effect of dietary cyclopropenoid fatty acids on hepatic microsomal polypeptide distribution patterns. Antibodies against rainbow trout type-LM2 cytochrome P-450 were employed to localize the corresponding polypeptide(s) by immunochemical staining. The LM2 antigen was purified from trout that had been fed beta-naphthoflavone. Microsomes from trout fed beta-naphthoflavone showed a decrease in a cytochrome P-450 polypeptide, detected with antibody against LM2. In contrast, microsomes from control fish contained two distinct cytochrome P-450 polypeptides, differing in their isoelectric points. Cyclopropenoid fatty acid treatment caused a preferential decrease in the additional isozyme seen in control samples. The distribution of concanavalin-A-binding glycopolypeptides was also assessed. Surprisingly, the two P-450 isozymes localized from control microsomes were found to bind concanavalin A. In addition to this, the cyclopropenoid fatty acid treatment generated a shift in a closely related group of microsomal glycopolypeptides, labeled gp80, gp82, gp80(1), and gp82(1). A decrease in the levels of gp80 and gp82 and a corresponding increase in gp80(1) and gp82(1) was observed.

Dietary modification of aflatoxin B1 carcinogenesis: mechanism studies with isolated hepatocytes from rainbow trout.

Hepatocytes were prepared from rainbow trout by perfusion in situ with collagenase and hyaluronidase. Preparations normally showed high initial viability (95 +/- 5% dye exclusion, 92 +/- 5% lactate dehydrogenase retention) and gradually decreased in viability and glutathione concentration over 5 hours. Cellular metabolism of aflatoxin B1 (AFB1), a potent hepatocarcinogen, was characterized by an investigation of the following parameters: kinetics of AFB1 metabolism and DNA adduct formation, dose response, viabilities of detoxication and activation pathways with time, influence of organic solvents, and effect of variation in cell concentration. The AFB1 metabolites and DNA adducts were resolved and quantitated by high-performance liquid chromatography. From these results a standardized assay procedure was derived which we used to examine AFB1 metabolism and DNA adduct formation in hepatocytes from fish fed dietary substances known to alter the carcinogenic response to this mycotoxin. Dietary beta-naphthoflavone, which strongly inhibits AFB1 carcinogenesis in rainbow trout, dramatically and reproducibly altered AFB1 binding and metabolism in isolated hepatocytes. Overall rate of AFB1 metabolism and rates of detoxication reactions increased, whereas DNA binding decreased. Dietary cyclopropenoid fatty acids, powerful synergists and promoters of AFB1 carcinogenesis in trout, also repressed AFB1-DNA binding. Both dietary factors appeared to depress initial DNA damage by AFB1 but operated through different metabolic pathways to do so.

In vitro and in vivo temperature modulation of hepatic metabolism and DNA adduction of aflatoxin B1 in rainbow trout.

Alterations in membrane lipid composition during temperature acclimation of poikilotherms is hypothesized to compensate for direct effects of temperature on membrane fluidity. Temperature also influences disposition and actions of some xenobiotics. This suggests the potential for complex interactions between temperature and metabolism of chemical carcinogens. Whole livers and hepatic microsomes from rainbow trout acclimated at 18 degrees C have more saturated fatty acids and less mono- and polyunsaturated fatty acids than those from fish acclimated at 10 degrees C. Such changes are consistent with a role for membrane lipid fluidity in temperature compensation. When 10 and 18 degrees C acclimated fish are ip injected with 0.4 mg/kg [3H]aflatoxin B1 (AFB1) at their respective acclimation temperatures, hepatic disposition of AFB1, DNA adduction, and biliary metabolites are similar. An acute shift of 18 degrees C acclimated trout to 14 degrees C reduces [3H]AFB-DNA adduct formation, while [3H]AFB1 adduction after acute shift of 10 degrees C acclimated fish to 14 degrees C is no different than in non-shifted fish. Hepatic microsomes isolated from 10 or 18 degrees C acclimated trout, incubated with 10 microM [3H]AFB1 and calf thymus DNA between 6 and 22 degrees C exhibit no differences in the "break points" of Arrhenius plots (16 degrees C in both groups). There is, however, more in vitro DNA adduction of [3H]AFB1 by microsomes from 18 degrees C acclimated fish, a difference abolished by 0.5 mM alpha-naphthoflavone (ANF). These results suggest that temperature acclimation of trout differentially modifies activities of cytochrome P-450 isozymes. When assayed at respective acclimation temperatures, hepatic cytosol from 18 degrees C fish produces more aflatoxicol, a detoxication product of AFB1, than cytosol from 10 degree C fish. Therefore, this soluble enzyme does not exhibit ideal temperature compensation. Such temperature-induced differences in microsomal cytochrome P-450 isozymes and cytosolic dehydrogenase partially explain temperature-modulated AFB1 genotoxicity.