Purification and properties of a chicken liver glutathione S-transferase

The Mechanism Underlying the Extreme Sensitivity of Duck to Aflatoxin B1

Most metabolites of aflatoxin B1 (AFB1), especially exo-AFB1-8,9-epoxide (AFBO), can induce the production of reactive oxygen species (ROS) to vary degrees, causing oxidative stress and liver damage, and ultimately induce liver cancer in humans and animals. Duck is one of the most sensitive animals to AFB1, and severe economic losses are caused by duck AFB1 poisoning every year, but the exact mechanism of this high sensitivity is still unclear. This review highlights significant advances in our understanding of the AFB1 metabolic activation, like cytochrome P450s (CYPs), and AFB1 metabolic detoxification, like glutathione S-transferases (GSTs) in poultry. In addition, AFB1 may have other metabolic pathways in poultry, such as the mutual conversion of AFB1 and aflatoxicol (AFL) and the process of AFBO to produce AFB1-8,9-dihydrodiol (AFB1-dhd) and further metabolize it into detoxification substances. This review also summarized some exogenous regulatory substances that can alleviate AFB1-induced oxidative stress.

Aflatoxin B1 in poultry: toxicology, metabolism and prevention

Aflatoxins (AF) are ubiquitous in corn-based animal feed and causes hepatotoxic and hepatocarcinogenic effects. The most important AF in terms of toxic potency and occurrence is aflatoxin B1 (AFB1). Poultry, especially turkeys, are extremely sensitive to the toxic and carcinogenic action of AFB1, resulting in millions of dollars in annual losses to producers due to reduced growth rate, increased susceptibility to disease, reduced egg production and other adverse effects. The extreme sensitivity of turkeys and other poultry to AFB1 is associated with efficient hepatic cytochrome P450-mediated bioactivation and deficient detoxification by glutathione S-transferases (GST). Discerning the biochemical and molecular mechanisms of this extreme sensitivity of poultry to AFB1, will contribute in the development of novel strategies to increase aflatoxin resistance. Since AFB1 is an unavoidable contaminant of corn-based poultry feed, chemoprevention strategies aimed at reducing AFB1 toxicity in poultry and in other animals have been the subject of numerous studies. This brief review summarizes many of the key recent findings regarding the action of aflatoxins in poultry.

Drug metabolizing enzyme systems in the houbara bustard (Chlamydotis undulata)

This study compared catalytic and immunochemical properties of drug metabolizing phase I and II enzyme systems in houbara bustard (Chlamydotis undulata) liver and kidney and rat liver. P450 content in bustard liver (0.34 +/- 0.03 nmol mg-1 protein) was 50% lower than that of rat liver (0.70 +/- 0.02 nmol mg-1 protein). With the exception of aniline hydroxylase activity, monooxygenase activities using aminopyrine, ethoxyresorufin and ethoxycoumarin as substrates were all significantly lower than corresponding rat liver enzymes. As found in mammalian systems the P450 activities in the bird liver were higher than in the kidney. Immunohistochemical analysis of microsomes using antibodies to rat hepatic P450 demonstrated that bustard liver and kidney express P4502C11 homologous protein; no appreciable cross-reactivity was observed in bustards using antibodies to P4502E1, 1A1 or 1A2 isoenzymes. Glutathione content and glutathione S-transferase (GST) activity in bustard liver were comparable with those of rat liver. GST activity in the kidney was 65% lower than the liver. Western blotting of liver and kidney cytosol with human GST isoenzyme-specific antibodies revealed that the expression of alpha-class of antibodies exceeds mu in the bustard. In contrast, the pi-class of GST was not detected in the bustard liver. This data demonstrates that hepatic and renal microsomes from the bustard have multiple forms of phase I and phase II enzymes. The multiplicity and tissue specific expression of xenobiotic metabolizing enzymes in bustards may play a significant role in determining the pharmacokinetics of drugs and susceptibility of the birds to various environmental pollutants and toxic insults.

Site-directed mutagenesis and chemical modification of histidine residues on an alpha-class chick liver glutathione S-transferase CL 3-3. Histidines are not needed for the activity of the enzyme and diethylpyrocarbonate modifies both histidine and lysine residues

Each chick liver glutathione S-transferase CL 3 subunit contains three histidine residues: His142, His158 and His228. CL 3-3 can be inactivated by treating with diethylpyrocarbonate. The inactivation process is pH dependent and the pKa of the modified residue is 6.4. The second-order inhibition rate constant is 741 M-1min-1 at pH 7.0. Based on difference-spectrum and kinetic analysis, inactivation coincides with the modification of one histidine residue. However, hydroxylamine treatment of the diethylpyrocarbonate-modified enzyme only partially restored the activity (30-50%) of CL 3-3. By tryptic mapping and amino acid sequence analysis, His228 and Lys14 have been identified as the modified residues. Mutants with histidine to serine replacement (H142S and H158S) or C-terminal histidine deletion (des-H228) were constructed and over-expressed in Spodoptera frugiperda cells using a baculovirus system. The mutants are enzymically active. Furthermore, the des-H228 mutant can be inactivated by diethylpyrocarbonate. These results support the conclusion that histidines are not involved in the enzymic mechanism of CL 3-3.

Purification and characterisation of glutathione transferase from the giant African snail, Archachatina marginata

1. Glutathione-S-transferase has been purified from the hepatopancreas of Archachatina marginata to homogeneity. 2. The enzyme was found to be a dimer with a molecular weight of 44,000. The subunits sizes were 22,500 and 23,500 respectively. The isoelectric points of the enzyme were 8.35, 7.95 and 4. The enzyme was most stable at temperature below 40 degrees C. Upon denaturation by 4 M urea, only 56% of the activity could be recovered. 3. The Kms for glutathione and 1-chloro-2,4-dinitrobenze (CDNB) were 0.23 mM and 0.4 mM respectively. The specific activity of the enzyme with CDNB and p-nitrophylacetate as substrates were 47 mumol/mg and 38 mumol/mg respectively. 4. Inhibition studies showed that S-hexylglutathione, Rose Bengal, iodoacetamide, sodium azide and Procion Blue H-B were good inhibitors with I50 values ranging from 18.5 microM to 299 mM. 5. The amino acid composition showed that the enzyme had a relatively high content of hydrophobic and acidic amino acid residues. The peptide maps of the tryptic digests of the native and performic acid-oxidised enzyme indicated that there might be about two disulphide bridges per molecule of the enzyme.

Cloning and expression of a chick liver glutathione S-transferase CL 3 subunit with the use of a baculovirus expression system

Glutathione S-transferase CL 3 subunits purified from 1-day-old-chick livers were digested with Achromobacter proteinase I and the resulting fragments were isolated for amino acid sequence analysis. An oligonucleotide probe was constructed accordingly for cDNA library screening. A cDNA clone of 1342 bases, pGCL301, encoding a protein of 26209 Da was isolated and sequenced. Including conservative substitutions, this protein has 75-79% sequence similarity to other Alpha family glutathione S-transferases. The coding sequence of pGCL301 was inserted into a baculovirus vector for infection of Spodoptera frugiperda (SF9) cells. The expressed protein has a high relative activity with ethacrynic acid (47% of the specific activity with 1-chloro-2,4-dinitrobenzene). The enzyme has a subunit molecular mass of 25.2 +/- 1.2 kDa (by SDS/PAGE), a pI of 9.45 and an absorption coefficient A1%1cm of 13.0 +/- 0.5 at 280 nm.

Nucleotide sequence of a class mu glutathione S-transferase from chicken liver

A clone coding for glutathione S-transferase (GST) CL2 was isolated from a chicken liver cDNA library. This clone (819 bp) encodes a polypeptide comprising 219 amino acids with a molecular weight of 25,717, excluding the initiator methionine. The primary amino acid sequence of the enzyme has 47% identical sequence with other class mu GSTs.

Comparison of glutathione S-transferase activity in the rat and birds: tissue distribution and rhythmicity in chicken (Gallus domesticus) liver

1. Mature, male chickens, Bobwhite quail, and rats differed with respect to glutathione S-transferase (GST) activity in the kidney, duodenum and testis, but species differences were not observed in the liver. 2. GST activity was present in the heart, spleen, liver, duodenum, kidney, testis, cerebral cortex, cerebellum, optic tecta, and medulla oblongata of chickens with differences in tissues and breeds. 3. Renal GST activity was higher in female chickens, whereas enzyme activity in the brain was higher in males. 4. Hepatic GST activity fluctuated about a mean of 784 nmol min-1 mg protein-1 with a 12 hr periodicity which was not a feeding phenomenon. 5. The results demonstrate that GST activity occurs in diverse tissues of the chicken and Bobwhite quail with kidney greater than liver greater than duodenum greater than testis, compared to testis greater than liver greater than duodenum greater than kidney in the rat. Hepatic GST activity exhibits an ultradian periodicity.

Sex and species differences in glutathione S-transferase activities

Glutathione S-transferases (GSTs) are one of the important enzymes in terms of not only drug metabolism but also physiological functions. The marked sex difference in GST activity has been found in rat and mouse liver cytosol, and such differences in rat liver are suggested to be primarily due to the differences in the subunit composition of GSTs in both sexes. In addition, GST activities of rat liver cytosol are known to be largely influenced by treatment with inducers such as phenobarbital and 3-methylcholanthrene and various hormones. GSTs are widely distributed in mammalian species, and multiplicity of GST has been demonstrated so far. The present review also describes multiple forms of GST from the viewpoint of enzymology and immunology.

Anionic and neutral glutathione S-transferase isoenzymes in the freshwater worm Tubifex tubifex (O.F.M.)

The anionic and the neutral glutathione S-transferase (GST) isoenzymes from the freshwater worm Tubifex tubifex (O.F.M.) were separated in one step by chromatofocusing on a Polybuffer exchanger 94 column, eluted with Polybuffer 74. Their pI values ranged between 4.12 and 6.98, and their molecular weight between 30 000 and 38 400. The apparent Km values towards glutathione and 1-chloro-2,4-dinitrobenzene were also determined. The high number of non-cationic GST isoenzymes is unusual. Tubifex worms seems well equipped for attacking environmental pollutants.

Effect of streptozotocin on the glutathione S-transferases of mouse liver cytosol

Streptozotocin (STZ) increased the activity of mouse hepatic glutathione (GSH) S-transferases assayed with 1-chloro-2,4-dinitrobenzene. Nicotinamide administered prior to STZ prevented the hyperglycemia indicative of STZ-induced diabetes, but had no effect on the increase in GSH S-transferase activity caused by the drug. Another diabetogenic agent, alloxan, did not alter GSH S-transferase activity. Thus, streptozotocin may be increasing GSH S-transferase activity directly, and not as a result of the diabetic state the drug induces. Two transferases were characterized from mouse liver cytosol. One was a homodimer with a subunit molecular weight of about 28,000 and a pI of about 8.2. The other was also a homodimer with a subunit molecular weight of about 27,500 and a pI of about 9.2. The pI 8.2 GSH S-transferase was induced by STZ, while the pI 9.2 transferase was decreased by the drug. At least one other transferase appeared to be induced by STZ. Two other nitroso compounds, chlorozotocin and diethylnitrosamine, also increased GSH S-transferase activity, suggesting that this effect may be nitroso related.

Purification and characterization of glutathione-S-transferase from liver cytosol of phenobarbital-treated rabbits

Glutathione-S-transferase (GST) from the liver cytosol of phenobarbital (PB)-treated rabbits was purified by DEAE-cellulose, CM-cellulose and hydroxylapatite column chromatography. Four species of GST were obtained by eluting the CM-cellulose column with a linear KCl gradient, and the major protein investigated. The purified enzyme from PB-treated and untreated rabbit had specific activities of 125.16 units/mg and 72.8 units/mg of protein, respectively, and the apparent Km was 0.6 X 10(-3) M for GSH and 1.6 X 10(-3) M for 1-chloro-2,4-dinitrobenzene. The optimum pH value was 8.7 and the enzyme was able to conjugate with 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, 1,2-epoxy-3-(p-nitrophenoxy)propane and p-nitrobenzyl chloride.

Alterations in drug metabolising enzymes and lipid peroxidation in different rat tissues by fluoride

Sodium fluoride at a dose level of 5.0 mg/kg enhanced aminopyrine N-demethylase and NADPH cytochrome c reductase activities and cytochrome P450 and cytochrome b5 levels in rat liver, kidney, lung, intestine and testis, whereas acetanilide hydroxylase activity remained unchanged in kidney and lung and was increased in liver, intestine and testis. Sodium fluoride at 20.0 mg/kg caused a decrease in aminopyrine N-demethylase, acetanilide hydroxylase and NADPH cytochrome c reductase activities and cytochrome P450 and cytochrome b5 levels in all tissues, except for an increase in NADPH cytochrome c reductase activity in the intestine and testis. Fluoride at both dose levels produced only marginal changes in glutathione-S-transferase activity except for a 4-fold increase in the testis at 5.0 mg/kg. Sodium fluoride at 5.0 mg/kg increased lipid peroxidation in all tissues studied. At 20.0 mg/kg there was a decrease in lipid peroxidation in liver, lung and testis and an increase in kidney and intestine.

The hepatic glutathione transferases of the male little skate, Raja erinacea

Five cytosolic glutathione transferases were isolated from the liver of the male little skate, Raja erinacea, a marine elasmobranch. They were designated E-1 through E-5 in order of their elution from a DEAE-cellulose column with a 0 to 100 mM KCl gradient in 0.01 M Tris (pH 8.0). Each eluted peak of glutathione transferase activity, after concentration, was applied to an affinity column prepared by reaction of epoxy-activated Sepharose 6B with glutathione (GSH). Elution of the various glutathione transferases from this column with GSH resulted in the further purification of each enzyme; the major glutathione transferase, E-4 and E-1, were purified to apparent homogeneity by this procedure. Skate glutathione transferase E-4 is dimeric and the subunits are either very similar or identical in molecular weight (about 26 000 daltons). Enzymes E-2 through E-5 were acidic proteins (pI less than 7.0) and had high specific glutathione transferase activity (0.3--12 mumol/min/mg protein) with benzo[a]pyrene 4,5-oxide (BPO) as substrate, whereas the other enzyme (E-1) had low activity (0.01 mumol/min/mg) with BPO and a basic pI (greater than 9.5). Bilirubin and hematin, non-substrate ligands, bound tightly to homogeneous E-4, with dissociation constants in the micromolar range.