Glutathione S-transferases in noral and malignant human colon tissue

This study focuses on the GST composition of a tissue intrinsically resistant to chemotherapy, the human colon. GSTs were purified from matched pairs of colon tissue (normal and tumor) using glutathione affinity chromatography. The mean GST activity of colon tumors was 1.5-fold higher than that of normal tissue, with tumors of the sigmoid colon showing the greatest increase (2.3-fold). Two-dimensional gel electrophoresis and Western blot analysis of purified enzymes demonstrated the presence of all three GST classes (α, μ and π) in colon, with GST π being both the predominant isozyme in normal and malignant tissues. The level of α class subunits was the same in normal and tumor tissues, while the μ class subunits were decreased in tumors. A protein copurifying with GSTs from both normal and tumor tissue did not crossreact with GST antibodies, but instead reacted with a polyclonal antibody to glyoxylase I. This enzyme existed as a dimer in its native state. Upon boiling, monomeric subunits were produced with a molecular mass of 22.6 kDa and an isoelectric point more acidic than GST π. Increased amounts of glyoxylase I were also found in tumor vs. normal colon. The apparent elevated levels of these glutathione-associated detoxifying enzymes in colon tumors may contribute to their intrinsic drug resistance.     

Immunohistochemical localization, purification, and characterization of human urinary bladder glutathione S-transferases

This study describes immunohistochemical localization, purification and characterization of glutathione S-transferase (GST) of human urinary bladder. Even though all the three major classes of isoenzymes (alpha, mu, and pi) were expressed in human bladder, more than 90% of total GST activity was accounted for by a pi class anionic form. Human bladder alpha, mu, and pi class GSTs were immunologically related to respective isoenzymes of other human tissues. GST pi was present in all 13 samples analyzed, whereas GST alpha and mu were detected in nine and eleven samples, respectively. GST alpha of human bladder appeared to be unique, because unlike this class of GSTs of other human tissues, bladder enzyme had lower affinity for GSH linked to epoxy-activated Sepharose 6B affinity resin. Immunohistochemical staining indicated localization of GST alpha in epithelial surface cells, underlying submucosa and smooth muscle, whereas mu and pi class isoenzymes were predominantly distributed in epithelial surface cells. These results suggest that human bladder GSTs may play an important role in providing protection against xenobiotics because epithelium is considered a target for several carcinogens and all the three classes of isoenzymes are expressed in these cells.     

Purification and characterization of human muscle glutathione S-transferases: evidence that glutathione S-transferase zeta corresponds to a locus distinct from GST1, GST2, and GST3.

Human muscle glutathione S-transferase isozyme, GST zeta (pI 5.2) has been purified by three different methods using immunoaffinity chromatography, DEAE cellulose chromatography, and isoelectric focusing. GST zeta prepared by any of the three methods does not recognize antibodies raised against the alpha, mu, or pi class glutathione S-transferases of human tissues. GST zeta has a blocked N-terminus and its peptide fingerprints also indicate it to be distinct from the alpha, mu, or pi class isozymes. As compared to GSTs of alpha, mu, and pi classes, GST zeta displays higher activities toward t-stilbene oxide and Leukotriene A4 methyl ester. GST zeta also expresses GSH-peroxidase activity toward hydrogen peroxide. The Kms of GST zeta for CDNB and GSH were comparable to those reported for other human GSTs but its Vmax for CDNB, 7620 mol/mol/min, was found to be considerably higher than that reported for other human GSTs. The kinetics of inhibition of GST zeta by hematin, bile acids, and other inhibitors also indicate that it was distinct from the three classes of GST isozymes. These studies suggest that GST zeta corresponds to a locus distinct from GST1, GST2, and GST3 and probably corresponds to the GST4 locus as suggested previously by Laisney et al. (1984, Human Genet. 68, 221-227). The results of peptide fingerprints and kinetic analysis indicate that as compared to the pi and alpha class isozymes, GST zeta has more structural and functional similarities with the mu class isozymes. Besides GST zeta several other GST isozymes belonging to pi and mu class have also been characterized in muscle. The pi class GST isozymes of muscle have considerable charge heterogeneity among them despite identical N-terminal sequences.     

Quantification of human hepatic glutathione S-transferases.

Human hepatic glutathione S-transferase (GST) subunits were characterized and quantified with the aid of a recently developed h.p.l.c. method. In 20 hepatic tissue specimens the absolute amounts of the basic Class Alpha subunits B1 and B2, the near-neutral Class Mu subunits mu and psi and the acidic subunit pi were determined. The average total amount of GST was 37 micrograms/mg of cytosolic protein, with the Class Alpha GST being the predominant class (84% of total GSTs), and pi as the sole representative of the Class Pi GSTs present in the lowest concentration (4% of total GSTs). Large interindividual differences were observed for all subunits, with variations up to 27-fold, depending on the subunit. For the Class Alpha GST-subunits B1 and B2, a biphasic ratio was observed. The genetic polymorphism of the subunits mu and psi was confirmed by h.p.l.c. analysis, and correlated with the enzymic glutathione conjugation of trans-stilbene oxide and with Western blotting of cytosols, using a monoclonal anti-(Class Mu GST) antibody. Of the 20 livers examined, ten contained only mu, whereas the occurrence of psi alone, and the combination of mu and psi, were found in only one liver each.     

Purification and subunit-structural and immunological characterization of five glutathione S-transferases in human liver, and the acidic form as a hepatic tumor marker

Five glutathione S-transferase (GST, EC 2.5.1.18) forms were purified from human liver by S-hexylglutathione affinity chromatography followed by chromatofocusing, and their subunit structures and immunological relationships to rat liver glutathione S-transferase forms were investigated. They were tentatively named GSTs I, II, III, IV and V in order of decreasing apparent isoelectric points (pI) on chromatofocusing. Their subunit molecular weights assessed on SDS-polyacrylamide gel electrophoresis were 27 (Mr X 10(-3)), 27, 27.7,27 and 26, respectively, (26, 26, 27, 26, and 24.5 on the assumption of rat GST subunit Ya, Yb and Yc as 25, 26.5 and 28, respectively), indicating that all forms are composed of two subunits identical in size. However, it was suggested by gel-isoelectric focusing in the presence of urea that GSTs I and IV are different homodimers, consisting of Y1 and Y4 subunits, respectively, which are of identical Mr but different pI, while GST II is a heterodimer composed of Y1 and Y4 subunits. This was confirmed by subunit recombination after guanidine hydrochloride treatment. GST III seemed to be identical with GST-mu with regard to Mr and pI. GST V was immunologically identical with the placental GST-pi. On double immunodiffusion or Western blotting using specific antibodies to rat glutathione S-transferases, GST I, II and IV were related to rat GST 1-1 (ligandin), GST III(mu) to rat GST 4-4 (D), and GST V (pi) to rat GST 7-7 (P), respectively. GST V (pi) was increased in hepatic tumors.     

A new class of rat glutathione S-transferase Yrs-Yrs inactivating reactive sulfate esters as metabolites of carcinogenic arylmethanols

A glutathione (GSH) S-transferase (GST), catalyzing the inactivation of reactive sulfate esters as metabolites of carcinogenic arylmethanols, was isolated from the male Sprague-Dawley rat liver cytosol and purified to homogeneity in 12% yield with a purification factor of 901-fold. The purified GST was a homo-dimeric enzyme protein with subunit Mr 26,000 and pI 7.9 and designated as Yrs-Yrs because of its enzyme activity toward "reactive sulfate esters." GST Yrs-Yrs could neither be retained on the S-hexylglutathione gel column nor showed any activity toward 1,2-dichloro-4-nitrobenzene, 4-nitrobenzyl chloride, and 1,2-epoxy-3-(4'-nitrophenoxy)propane. 1-Chloro-2,4-dinitro-benzene was a very poor substrate for this GST. 1-Menaphthyl sulfate was the best substrate for GST Yrs-Yrs among the examined mutagenic arylmethyl sulfates. The enzyme had higher activities toward ethacrynic acid and cumene hydroperoxide. N-terminal amino acid sequence of subunit Yrs, analyzed up to the 25th amino acid, had no homology with any of the known class alpha, mu, and pi enzymes of the Sprague-Dawley rat. Anti-Yrs-IgG raised against GST Yrs-Yrs showed no cross-reactivity with any of subunits Ya, Yc, Yb1, Yb2, and Yp. Anti-IgGs raised against Ya, Yc, Yb1, Yb2, and Yp also showed no cross-reactivity with GST Yrs-Yrs. The purified enzyme proved to differ evidently from the 12 known cytosolic GSTs in various tissues of the rat in all respects. Immunoblot analysis of various tissue cytosols of the male rat indicated that apparent concentrations of the GST Yrs-Yrs protein were in order of liver greater than testis greater than adrenal greater than kidney greater than lung greater than brain greater than skeletal muscle congruent to heart congruent to small intestine congruent to spleen congruent to skin congruent to 0.     

Expression of glyoxalase, glutathione peroxidase and glutathione S-transferase isoenzymes in different bovine tissues

(1) The tissue-specific expression of various glutathione-dependent enzymes, including glutathione S-transferase (GST), glutathione peroxidase and glyoxalase I, has been studied in bovine adrenals, brain, heart, kidney, liver, lung and spleen. Of the organs studied, liver was found to possess the greatest GST and glyoxalase I activity, and spleen the greatest glutathione peroxidase activity. The adrenals contained large amounts of these glutathione-dependent enzymes, but significant differences were observed between the cortex and medulla. (2) GST and glyoxalase I activity were isolated by S-hexylglutathione affinity chromatography. Glyoxalase I was found in all the organs examined, but GST exhibited marked tissue-specific expression. (3) The alpha, mu and pi classes of GST (i.e., those that comprise respectively Ya/Yc, Yb/Yn and Yf subunits) were all identified in bovine tissues. However, the Ya and Yc subunits of the alpha class GST were not co-ordinately regulated nor were the Yb and Yn subunits of the mu class GST. (4) Bovine Ya subunits (25.5-25.7 kDa) were detected in the adrenal, liver and kidney, but not in brain, heart, lung or spleen. The Yc subunit (26.4 kDa) was expressed in all those organs which expressed the Ya subunit, but was also found in lung. The mu class Yb (27.0 kDa) and Yn (26.1 kDa) subunits were present in all organs; however, brain, lung and spleen contained significantly more Yn than Yb type subunits. The pi class Yf subunit (24.8 kDa) was detected in large amounts in the adrenals, brain, heart, lung and spleen, but not in kidney or liver. (5) Gradient affinity elution of S-hexylglutathione-Sepharose showed that the bovine proteins that bind to this matrix elute in the order Ya/Yc, Yf, Yb/Yn and glyoxalase I. (6) In conclusion, the present investigation has shown that bovine GST are much more complex than previously supposed; Asaoka (J. Biochem. 95 (1984) 685-696) reported the purification of mu class GST but neither alpha nor pi class GST were isolated.     

Amino acid sequence of glutathione S-transferase b from guinea pig liver

The amino acid sequence of glutathione S-transferase b (GST b) from guinea pig liver was determined by conventional methods. GST b was composed of two identical subunits, each with 217 amino acid residues. As GSTs are generally classified into three classes, alpha, mu, and pi, GST b belonged to class mu and the amino acid sequence of GST b showed about 80% homology with that of rat GST Yb.     

A Pi Form of Glutathione-S-Transferase Is a Myelin-and Oligodendrocyte-Associated Enzyme in Mouse Brain

The pi form of glutathione-S-transferase (GST), previously found to be oligodendrocyte associated, has also been found in myelin. In the brains of adult mice, immunocytochemical staining for a pi form of GST was observed in myelinated fibers, as well as oligodendrocytes. In contrast, and as previously found in rats, positive immunostaining for mu forms occurred in astrocytes and not in oligodendrocytes or myelinated fibers. Double immunofluorescence staining strengthened the conclusion that pi was in oligodendrocytes and myelin in mouse brains. The results of enzyme assays performed on brain homogenates and purified myelin indicated that GST specific activities in mouse brain myelin were almost as high (0.8-fold) as those in mouse brain homogenates. Low, but reproducible, GST activities were also observed in myelin purified from rat brains, in which pi had been demonstrated in oligodendrocytes and mu in astrocytes. The pi form was also stained by the immunoblot technique in myelin purified from mouse brain. It was concluded that pi is a myelin associated, as well as oligodendrocyte associated, enzyme in mouse brain, and possibly also in rat brain. This is the first report of localization of GSTs in mouse brain and of GST in myelin.     

Distribution of glutathione S-transferase isoenzymes in human ovary.

Glutathione S-transferases (GST) are drug-metabolizing and detoxification enzymes involved in the intracellular transport and metabolism of steroid hormones. We studied expression of pi, alpha, mu and microsomal GST by immunohistochemistry in normal human ovaries at different stages of the menstrual cycle and pregnancy and after the menopause. Antibodies were raised in rabbits to purified GST subunits and formalin-fixed, paraffin-embedded sections were studied using the peroxidase-antiperoxidase method. Staining density was graded from very strong to negative. All four isoenzymes were identified in the ovary and their distribution was heterogeneous. The staining pattern of follicles varied with the stage of the menstrual cycle for each isoenzyme. All the ovaries contained abundant GST pi in stroma. GST alpha is closely associated with the glutathione-dependent enzyme delta-5,3-ketosteroid isomerase, which catalyses the conversion of pregnenolone to progesterone and dehydroepiandrosterone to androstenedione. GST alpha was localized to the steroid-producing cells and thus may be useful in studying ovaries in conditions where there are assumed alterations in steroid production.     

Differential expression of alpha, mu and pi classes of isozymes of glutathione S-transferase in bovine lens, cornea, and retina

Isozyme characterization of glutathione S-transferase (GST) isolated from bovine ocular tissue was undertaken. Two isozymes of lens, GST 7.4 and GST 5.6, were isolated and found to be homodimers of a Mr 23,500 subunit. Amino acid sequence analysis of a 20-residue region of the amino terminus was identical for both isozymes and was identical to GST psi and GST mu of human liver. Antibodies raised against GST psi cross-reacted with both lens isozymes. Although lens GST 5.6 and GST 7.4 demonstrated chemical and immunological relatedness, they were distinctly different as evidenced by their pI and comparative peptide fingerprint. A corneal isozyme, GST 7.2, was also isolated and established to be a homodimer of Mr 24,500 subunits. Sequence analysis of the amino-terminal region indicated it to be about 67% identical with the GST pi isozyme of human placenta. Antibodies raised against GST pi cross-reacted with cornea GST 7.2. Another corneal isozyme, GST 8.7, was found to be homodimer of Mr 27,000 subunits. Sequence analysis revealed it to have a blocked amino-terminus. GST 8.7 immunologically cross-reacted with the antibodies raised against cationic isozymes of human liver indicating it to be of the alpha class. Two isozymes of retina, GST 6.8 and GST 6.3, were isolated and identified to be heterodimers of subunits of Mr 23,500 and 24,500. Amino-terminal sequence analysis gave identical results for both retina GST 6.8 and GST 6.3. The sequence analysis of the Mr 23,500 subunit was identical to that obtained for lens GSTs. Similarly, sequence analysis of the Mr 24,500 subunit was identical to that obtained for the cornea GST 7.2 isozyme. Both the retina isozymes cross-reacted with antibodies raised against human GST psi as well as GST pi. The results of these studies indicated that all three major classes of GST isozymes were expressed in bovine eye but the GST genes were differentially expressed in lens, cornea, and retina. In lens only the mu class of GST was expressed, whereas cornea expressed alpha and pi classes and retina expressed mu and pi classes of GST isozymes.     

Purification and characterization of glutathione S-transferases of human kidney.

Several forms of glutathione S-transferase (GST) are present in human kidney, and the overall isoenzyme pattern of kidney differs significantly from those of other human tissues. All the three major classes of GST isoenzymes (alpha, mu and pi) are present in significant amounts in kidney, indicating that GST1, GST2 and GST3 gene loci are expressed in this tissue. More than one form of GST is present in each of these classes of enzymes, and individual variations are observed for these classes. The structural, immunological and functional properties of GST isoenzymes of three classes differ significantly from each other, whereas the isoenzymes belonging to the same class have similar properties. All the cationic GST isoenzymes of human kidney except for GST 9.1 are heterodimers of 26,500-Mr and 24,500-Mr subunits. GST 9.1 is a dimer of 24,500-Mr subunits. All the cationic isoenzymes of kidney GST cross-react with antibodies raised against a mixture of GST alpha, beta, gamma, delta and epsilon isoenzymes of liver. GST 6.6 and GST 5.5 of kidney are dimers of 26,500-Mr subunits and are immunologically similar to GST psi of liver. Unlike other human tissues, kidney has at least two isoenzymes (pI 4.7 and 4.9) associated with the GST3 locus. Both these isoenzymes are dimers of 22,500-Mr subunits and are immunologically similar to GST pi of placenta. Some of the isoenzymes of kidney do not correspond to known GST isoenzymes from other human tissues and may be specific to this tissue.     

The unique feature of dog liver cytosolic glutathione S-transferases. An isozyme not retained on the affinity column has the highest activity toward 1,2-dichloro-4-nitrobenzene

In the adult dog liver cytosol we identified four glutathione S-transferase (GST) subunits, Yd1 (Mr 26,000), Yd2 (Mr 27,000), Yd3 (Mr 28,000), and Ydf (Mr 27,400), and purified GST forms comprising Yd1, Yd2, and Yd3, to apparent homogeneity. Unlike rat transferases the enzyme activity toward 1,2-dichloro-4-nitrobenzene (DCNB) was not retained on the affinity column. Thus the DCNB-active enzyme, GST YdfYdf, from the flow-through fraction of the affinity column was also purified to homogeneity by gel filtration, DE52 chromatography, chromatofocusing, and hydroxylapatite column chromatography. Immunoblot analysis of dog GSTs revealed that the subunits Yd1, Yd2, and Yd3 belong to the pi, alpha, and mu class, respectively. On the contrary, Ydf had no reactivity with antibodies raised against any of the three classes of GST. Each subunit, Yd1, Yd2, Yd3, and Ydf, was distinguishable by its own retention time on reverse-phase high performance liquid chromatography. N-terminal amino acid sequences of the dog GSTS Yd1Yd1 and Yd3Yd3 revealed a high degree of homology to the pi and mu class transferases from rat, human, and mouse, respectively, while the N terminus of Yd2Yd2 is blocked. N-terminal amino acid sequences of GST YdfYdf showed no homology to any of the three classes of GST. The most significant property noted of GST YdfYdf is the high specific activity toward DCNB, exceeding by 1 order of magnitude the corresponding values for the known mu class GSTs. The present results strongly suggest that dog GST YdfYdf is a unique enzyme distinct from the hitherto characterized GST isozymes.     

Activation of rat glutathione transferases in class mu by active oxygen species

The activities of rat glutathione transferases (GSTs) 3-3, 3-4, 4-4 in Class mu towards 1-chloro-2,4-dinitrobenzene (CDNB) but not 1,2-dichloro-4-nitrobenzene were increased up to 5-fold during preincubation with 0.4 mM xanthine and xanthine oxidase in 50 mM potassium phosphate, pH 7.8, containing 0.1 mM EDTA. The activated GST 3-4, purified by S-hexylglutathione affinity chromatography after the treatment, had a higher specific activity (130 units/mg) than that of the nontreated (35 units/mg), the Km and Vmax values for glutathione or CDNB also were increased. Other rat GSTs in Class alpha and pi were inactivated by the same treatment. In the presence of superoxide dismutase, the activation of GST 3-4 did not occur.     

Characterization of glutathione transferase from Gammarus italicus.

1. By using affinity chromatography and chromatofocusing analysis at least two major glutathione transferases, named GST II and GST III can be isolated from Gammarus italicus. 2. GST II has an isoelectric point at pH 5.0 and is composed of two subunits with an apparent molecular mass of 28 KDa. 3. GST III which has an isoelectric point at pH 4.6 was found to be an heterodimer of 27 KDa and 28 KDa. 4. The 28 KDa subunit cross-reacted in immunoblotting analysis with antisera raised against pi class GST, whereas none of the antisera raised against alpha, mu and pi class GSTs cross-reacted with the 27 KDa subunit.     

Conjugation of isoprene monoepoxides with glutathione, catalyzed by alpha, mu, pi and theta-class glutathione S-transferases of rat and man

In the present study, the enzymatic conjugation of the isoprene monoepoxides 3,4 epoxy-3-methyl-1-butene (EPOX-I) and 3,4-epoxy-2-methyl-1-butene (EPOX-II) with glutathione was investigated, using purified glutathione S-transferases (GSTs) of the alpha, mu, pi and theta-class of rat and man. HPLC analysis of incubations of EPOX-I and EPOX-II with [35S]glutathione (GSH) showed the formation of two radioactive fractions for each isoprene monoepoxide. The structures of the EPOX-I and EPOX-II GSH conjugates were elucidated with 1H-NMR analysis. As expected, two sites of conjugation were found for both isoprene epoxides. EPOX-II was conjugated more efficiently than EPOX-I. In addition, the mu and theta class glutathione S-transferases were much more efficient than the alpha and pi class glutathione S-transferases, both for rat and man. Because the mu- and theta-class glutathione S-transferases are expressed in about 50 and 40-90% of the human population, respectively, this may have significant consequences for the detoxification of isoprene monoepoxides in individuals who lack these enzymes. Rat glutathione S-transferases were more efficient than human glu tathione S-transferases: rat GST T1-1 showed about 2.1-6.5-fold higher activities than human GST T1-1 for the conjugation of both EPOX-I and EPOX-II, while rat GST M1-1 and GST M2-2 showed about 5.2-14-fold higher activities than human GST M1a-1a. Most of the glutathione S-transferases showed first order kinetics at the concentration range used (50-2000 microM). In addition to differences in activities between GST-classes, differences between sites of conjugation were found. EPOX-I was almost exclusively conjugated with glutathione at the C4-position by all glutathione S-transferases, with exception of rat GST M1-1, which also showed significant conjugation at the C3-position. This selectivity was not observed for the conjugation of EPOX-II. Incubations with EPOX-I and EPOX-II and hepatic S9 fractions of mouse, rat and man, showed similar rates of GSH conjugation for mouse and rat. Compared to mouse and rat, human liver S9 showed a 25-50-fold lower rate of GSH conjugation.     

Characterization of two mu class glutathione S-transferases from guinea pig lens

Glutathione S-transferase (GST) plays an important role in the detoxifications of foreign electrophiles. Two GSTs of class mu from guinea pig lens were purified with Sephacryl S-100 gelfiltration, S-Hexyl glutathione Agarose affinity and Q-Sepharose anion exchange chromatographies. These GSTs (GST-A and B) showed similar relative molecular masses of 22.9 and 22.5 kDa, respectively. Two protein bands which crossreacted with anti GSTYb1 (GST 3-3) were detected in lens cytosolic crude extract on Western blotting and they showed Mrs corresponding to the purified enzymes. These GSTs showed a strong resistance against H2O2, 1,2-naphthoquinone and superoxide anion consistent with the other GSTs in class mu from animal tissues.     

Purification and characterization of glutathione S-transferases from rat pancreas

Glutathione S-transferases (GSTs) of rat pancreas have been characterized and their interrelationship with fatty acid ethyl ester synthase (FAEES) has been studied. Seven GST isozymes with pI values of 9.2, 8.15, 7.8, 7.0, 6.3, 5.9 and 5.4 have been isolated and designated as rat pancreas GST suffixed by their pI values. Structural, immunological and kinetic properties of these isozymes indicated that GST 9.2 belonged to the alpha class, GST 7.8, 7.0, 6.3 and 5.9 belonged to the mu class, whereas GST 8.15 and 5.4 belong to pi class. The N-terminal sequences and pI values of the mu class isozymes suggested that rat GST subunits 3, 4 and 6 may be expressed in pancreas. N-Terminal sequences of both the pi class isozymes, GST 8.15 and 5.4, were similar to that of GST-P, but there were significant differences in the substrate specificities of these two enzymes. Results of peptide finger print studies also indicated minor structural differences between these two isozymes. None of the GST isozymes of rat pancreas expressed FAEES activity. Rat pancreas had a significant amount of FAEES activity, but it segregated independently during the purification of GST indicating that these two activities are expressed by different proteins and are not related as suggested previously.     

Do the major human glutathione S-transferases have fatty acid ethyl ester synthase activity?

Two fatty acid ethyl ester (FAEE) synthase isoenzymes purified from human myocardium were reported to be glutathione S-transferases (GST) [(1989) Proc. Natl. Acad. Sci. USA 86, 4470-4473; and (1989) J. Clin. Invest. 84, 1942-1946]. In the present study, the FAEE synthase activity of several purified and well characterized human GSTs were examined with ethanol and [14C]oleic acid as substrates. Three isoenzymes, GST1, GST2 and GST3 which are members of the evolutionary classes mu, alpha, and pi, respectively, were studied and failed to show any significant synthesis of FAEE after 45 min incubation at 37 degrees C. FAEE synthase activity and GST3 activity in human placental extracts can be readily separated by ion exchange chromatography on DEAE cellulose. Thus the results show that FAEE synthase activity is not a feature of the major GSTs found in human tissues. The two FAEE synthase isoenzymes isolated by Bora et al. may have been co-purified with GST isoenzymes or these FAEE synthases may be members of the GST super family that have low specific activity in conventional GST assays and have not been previously described.