Independent segregation of glutathione S-transferase and fatty acid ethyl ester synthase from pancreas and other human tissues

Glutathione S-transferase (GST) isoenzymes of human pancreas were purified, characterized and evaluated for their possible role in the metabolism of ethanol. Human pancreas has at least two GST isoenzymes belonging to the Alpha class (pI 8.8 and 8.1), one belonging to the Mu class (pI 6.4) and one belonging to the Pi class (pI 4.9). During the purification of GSTs from pancreas as well as from heart, liver, lung, brain and muscle, the fatty acid ethyl ester synthase (FAEES) activity was monitored in order to evaluate the role of GSTs in metabolism of ethanol, as suggested in earlier studies. Both t.l.c. and h.p.l.c. were used to identify ethyl oleate in reaction mixtures to monitor FAEES activity. During the purification of GSTs with the use of affinity chromatography on GSH linked to epoxy-activated Sepharose 6B, FAEES and GST activities from each of these tissues segregated independently. Purified GST isoenzymes from these tissues did not exhibit any FAEES activity. Antibodies raised against Pi-class GST, as expected, immunoprecipitated most of the GST activity of brain and heart without precipitating FAEES activity. These results suggest that human GST isoenzymes belonging to the Alpha, Mu and Pi classes do not express FAEES activity. The independent segregation of GST and FAEES activities was further demonstrated by monitoring GST activity during the purification of FAEES from pancreas. It was found that purified FAEES had no GST activity towards 1-chloro-2,4-dinitrobenzene and a number of other electrophilic substrates. Results of these studies demonstrate that FAEES and GSTs are distinct proteins.

The anionic conjugates of bilirubin and bile acids stimulate ATP hydrolysis by S-(dinitrophenyl)glutathione ATPase of human erythrocyte

These studies demonstrate that bilirubin-ditaurate (an analog of bilirubin-diglucuronide), lithocholic acid 3-O-sulfate, and lithocholic acid 3-O-glucuronide, which are believed to be transported from liver into bile through an active transport process stimulate ATP hydrolysis by purified dinitrophenylglutathione ATPase of human erythrocytes. The Km and Vmax values of the enzyme for these substrates are similar to those for dinitrophenylglutathione indicating the transport mechanisms for bilirubin conjugates, and anionic bile acid-conjugates from hepatocytes to bile and transport of GSH-conjugates from erythrocytes may be mediated by similar mechanisms.

Purification and characterization of an ATPase from human liver which catalyzes ATP hydrolysis in the presence of the conjugates of bilirubin bile acids and glutathione

An ATPase has been purified from the membrane fraction of human liver which catalyzes ATP in the presence of bilirubin ditaurate, lithocholic acid 3-O-sulfate and lithocholic acid 3-O-glucuronide as well as dinitrophenylglutathione and other glutathione conjugates. Its subunit Mr value (38,000) and immunological properties are similar to dinitrophenylglutathione ATPase of human erythrocytes. Kinetic constants of the enzyme for the conjugates of glutathione, bile acids and bilirubin are comparable indicating that this ATPase may mediate active transport of all these anionic conjugates in liver.

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.

Purification and characterization of dinitrophenylglutathione ATPase of human erythrocytes and its expression in other tissues

S-(2,4-dinitrophenyl)glutathione (Dnp-SG) ATPase of human erythrocytes has been purified to apparent homogeneity by affinity chromatography. In reduced denaturing gels, the subunit Mr value of Dnp-SG ATPase was found to be 38,000. Dinitrophenyl glutathione (Dnp-SG) stimulated the hydrolysis of ATP by the purified enzyme whereas oxidized glutathione (GSSG) did not, indicating that Dnp-SG and GSSG are transported from the erythrocytes by different transporters. Results of Western blot analysis using the antibodies against Dnp-SG ATPase subunits indicated that the enzyme was expressed in human liver, lung, placenta and pancreas.

Stimulation of a human erythrocyte membrane ATPase by glutathione conjugates

An ATP-dependent transport process for S-(2,4-dinitrophenyl) glutathione (Dnp-SG) mediated by a novel ATPase designated as Dnp-SG ATPase has been demonstrated in human erythrocytes (LaBelle et al., FEBS Lett. 228, 53-51, 1988). In order to investigate whether the Dnp-SG ATPase system represents a generalized mechanism for the transport of xenobiotic conjugates of glutathione (GSH), stimulation of this ATPase by different GSH conjugates was studied in membrane vesicles prepared from human erythrocytes. Kinetic parameters for several GSH conjugates including S-(methyl)glutathione, S-(n-propyl)glutathione, S-(n-pentyl)glutathione, S-(n-decyl)glutathione, S-(p-chlorophenacyl)glutathione, S-(p-nitrobenzyl)glutathione, and the GSH conjugate of 9,10-epoxystearic acid were determined in order to evaluate their affinity for Dnp-SG ATPase. These studies reveal that all these conjugates stimulated Dnp-SG ATPase of human erythrocyte membrane. The apparent Km values of Dnp-SG ATPase for different conjugates were found to be in the range of 0.26-0.66 mM with Vmax values ranging from 0.55 to 4.44 nmol/min/mg protein. The results of these studies indicate that erythrocyte membrane Dnp-SG ATPase represents a generalized mechanism for the transport of GSH conjugates formed with xenobiotics as well as with the endogenously generated electrophilic compounds such as epoxystearic acid. It is suggested that Dnp-SG ATPase in conjunction with GSH and GSH S-transferase may play an important role in the protection of erythrocytes from exogenous as well as endogenous electrophilic toxicants.

Characterization of a novel alpha-class anionic glutathione S-transferase isozyme from human liver

A novel, alpha-class glutathione S-transferase (GST) isozyme has been isolated from human liver using glutathione (GSH) affinity chromatography, DEAE-cellulose ion-exchange chromatography, and immunoaffinity chromatography. The isozyme is a dimer of approximately 25,000 Mr with blocked N termini. Structural, kinetic, and immunological properties of this enzyme indicate that it belongs to the alpha class of GSTs. Noticeable differences between the properties of this enzyme and the other alpha-class GSTs of human liver are its anionic nature (pI 5.0), GSH peroxidase activity toward hydrogen peroxide, and relatively higher GSH conjugating activities toward CDNB and epoxide substrates as compared to other alpha-class GSTs. Results of these studies indicate that anionic GST omega characterized previously (Y. C. Awasthi, D. D. Dao, and R. P. Saneto, 1980, Biochem. J. 191, 1-10) from human liver is a mixture of GST pi and a novel alpha-class GST. We have, therefore, reassigned the name GST omega to this new alpha-class anionic GST of human liver.

Primary and secondary structural analyses of glutathione S-transferase pi from human placenta

The primary structure of glutathione S-transferase (GST) pi from a single human placenta was determined. The structure was established by chemical characterization of tryptic and cyanogen bromide peptides as well as automated sequence analysis of the intact enzyme. The structural analysis indicated that the protein is comprised of 209 amino acid residues and gave no evidence of post-translational modifications. The amino acid sequence differed from that of the deduced amino acid sequence determined by nucleotide sequence analysis of a cDNA clone (Kano, T., Sakai, M., and Muramatsu, M., 1987, Cancer Res. 47, 5626-5630) at position 104 which contained both valine and isoleucine whereas the deduced sequence from nucleotide sequence analysis identified only isoleucine at this position. These results demonstrated that in the one individual placenta studied at least two GST pi genes are coexpressed, probably as a result of allelomorphism. Computer assisted consensus sequence evaluation identified a hydrophobic region in GST pi (residues 155-181) that was predicted to be either a buried transmembrane helical region or a signal sequence region. The significance of this hydrophobic region was interpreted in relation to the mode of action of the enzyme especially in regard to the potential involvement of a histidine in the active site mechanism. A comparison of the chemical similarity of five known human GST complete enzyme structures, one of pi, one of mu, two of alpha, and one microsomal, gave evidence that all five enzymes have evolved by a divergent evolutionary process after gene duplication, with the microsomal enzyme representing the most divergent form.

ATP dependent primary active transport of xenobiotic-glutathione conjugates by human erythrocyte membrane

We have demonstrated the presence of a dinitrophenyl glutathione (Dnp-SG) stimulated ATPase in human erythrocyte membranes. This ATPase mediates the active transport of glutathione-xenobiotic conjugate such as Dnp-SG from erythrocytes into the plasma. It is suggested that this transport system is distinct from the system which actively transports oxidized glutathione from the erythrocytes.

Glutathione S-transferases and glutathione peroxidases in doxorubicin-resistant murine leukemic P388 cells

Energy-dependent rapid drug efflux is believed to be a major factor in cellular resistance to doxorubicin (DOX). However, several recent studies have demonstrated that cellular DOX retention alone does not always correlate with its cytotoxicity and suggest that mechanisms other than rapid drug efflux may also be important. In the present study, we have compared glutathione (GSH) S-transferase (GST), selenium-dependent GSH peroxidase and selenium-independent GSH peroxidase II activities in DOX-sensitive (P388/S) and resistant (P388/R) mouse leukemic cells. The GST activity towards 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (EA) was markedly higher in P388/R cells compared to P388/S cells. Purification of GST by GSH-affinity chromatography from an equal number of P388/S and P388/R cells revealed an increased amount of GST protein in P388/R cells. Immunological studies indicated that alpha and pi type GST isoenzymes were 1.27- and 2.2-fold higher, respectively, in P388/R cells compared to P388/S cells. Selenium-dependent GSH peroxidase activity was similar in both the cell lines, whereas selenium-independent GSH peroxidase II activity was approximately 1.36-fold higher in P388/R cells compared to P388/S cells. These results suggest that increased GSH peroxidase II activity in P388/R cells may contribute to cellular DOX resistance by enhancing free radical detoxification in this cell line.

Glutathione and glutathione S-transferases in a human plasma cell line resistant to melphalan

We report the development of a melphalan-resistant HS-Sultan human plasma cell line. The melphalan-resistant [MEL(R)] cell line was 16.7-fold more resistant to melphalan in vitro than the parent cell line [MEL(S)]. The wild type and MEL(R) HS-Sultan cell lines formed localized plasmacytomas when injected into nude mice. A dose-response effect of melphalan against the drug-sensitive plasmacytomas was present in vivo. A dose of 10 mg/kg of melphalan, which caused a 90% regression of MEL(S) plasmacytomas, had no effect on the MEL(R) plasmacytomas in vivo. In contrast to previous reports, there was no increase in the levels of glutathione (GSH) in the MEL(S) and MEL(R) plasmacytomas, suggesting that the association of elevated glutathione levels and melphalan resistance may not be common to all drug-resistant lines. In the MEL(R) plasmacytomas, there was a 1.5-fold induction of a pi type glutathione S-transferase (GST) as evidenced by isoelectric focusing (IEF) and Western blotting. This GST isoenzyme was purified and, although immunochemically similar to the pi type isoenzymes induced in other drug-resistant cell lines, was noted to have different functional characteristics. These data suggest that, depending on cell type and the drug studied, functionally different GST isoenzymes may be induced and they could be of importance in the development of drug resistance.

Glutathione S-transferase of bovine iris and ciliary body: characterization of isoenzymes

Five forms of glutathione (GSH) S-transferase (GST) having catalytic activities towards a variety of xenobiotics were present in bovine iris-ciliary body. In contrast to that in lens, cornea, and retina, GST isoenzymes belonging to all the three classes (alpha, mu and pi) were present in iris as well as in the ciliary body. GST isoenzymes of iris-ciliary body had pI values of 8.7, 7.4, 7.0, 6.6, and 6.0. GST 8.7 and GST 7.4 were apparent homodimers of 27,000 and 22,500 Mr subunits, respectively. GST 8.7 cross-reacted only with antibodies raised against the alpha class GST of human liver and GST 7.4 cross-reacted with the antibodies raised against GST pi of human placenta. GST 7.0 and 6.6 were heterodimers of Mr 26,500 and 25,000 subunits and both these subunits cross-reacted with the antibodies raised against the mu class human GST. Iris-ciliary body contained both, GSH peroxidase I and GSH peroxidase II activities and in this respect also, they differ from lens, cornea, and retina each of which have only one of these two activities. The presence of several GST isoenzymes belonging to all the three major classes and both GSH peroxidase I and II activities in iris-ciliary body may be important for the detoxification of oxidants and xenobiotics in order to prevent their infiltration in aqueous humor.

Anionic glutathione S-transferases of human erythrocytes, placenta, and lung: evidence for structural differences

Studies were undertaken to elucidate the structural interrelationships among glutathione S-transferase (GST) isozymes of human placenta, lung, and erythrocytes. Results of the high-performance liquid chromatography of the trypsin digests of the three isozymes indicate minor but significant differences in their elution profiles. Although a number of peptides generated by proteolysis were common for either 2 or 3 of the isozymes, significant differences were observed in elution profiles of other peptides. Qualitative as well as quantitative differences were also observed in the electrophoretic peptide maps of these isozymes. These studies suggest that there may be fine structural differences among the pi class GST isozymes of human tissues.

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.

Glutathione S-transferase isoenzymes in human lung tumors

In the present studies we have compared the levels of glutathione (GSH) and GSH-related enzymes in lung tumors and corresponding normal tissues obtained from the same individuals. We have also immunologically quantitated the relative amounts of glutathione S-transferase pi (or GST-P) type antigen in tumors and adjacent normal tissues from five patients. GST activities towards 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid were found to be elevated in tumors from two out of five patients (patients #1 and 4), whereas the activity towards these substrates was markedly suppressed in the tumor tissue from one of the patients (#5). Immunotitration and Western blot studies using antibodies raised against pi-type GST isoenzymes of human lung and placenta indicated induction of GST pi-type isoenzyme in tumors from patients #1 and 4 and suppression of this isoenzyme in tumor from patient #5. The tumors from patients #2 and 3 did not show any increase in GST activity or GST pi-type antigen. Except for the tumor from patient #5, the GSH content was higher in the tumors from other patients. GSH reductase activity was found to be elevated in tumors of all the patients examined in this study. These results indicate that GSH and GSH related enzymes are differentially altered in lung tumors and GSH levels and GST pi- or GST-P-type isoenzyme(s) are not uniformly elevated in all tumors.

Purification and characterization of unique glutathione S-transferases from human muscle

Results of studies designed to investigate the origin of the diversity of glutathione S-transferase (GST) isozymes in human tissues indicated that human muscle has at least three forms of GST with pI values of 5.0, 5.1, and 5.2 that are distinct from GST isozymes characterized so far. The major muscle isozyme which was expressed in all the six samples analyzed in this study was a unique GST of pI 5.2 that was designated as GST zeta. It had a blocked N-terminal and did not correspond to any of the known three classes (alpha, mu, or pi) of human GST as evidenced by its immunological properties and substrate specificities. The N-terminal regions of human muscle GST 5.1 and 5.0 had identical amino acid sequences except at residue 5, but demonstrated significant differences in amino acid composition and substrate specificities. These two isozymes showed homology with the mu class of human GST in their N-terminal region and were also immunologically related to the mu class of human GST although their subunit molecular weight values (Mr 23,000) were lower than that reported for GST psi. The substrate specificities of these isozymes were also significantly different from those of other human GST isozymes characterized so far. Significantly, muscle tissue did not express the alpha class of GST isozymes; however, two other isozymes were identified, GST 4.8 and GST 4.5, which had identical N-terminal amino acid sequences that were similar to that reported for the pi class of human GST. GST 4.8 was present in all six samples analyzed in this study whereas GST 4.5 was present in only two of these samples, indicating a possibility of polymorphism at the GST3 locus. This study indicated the occurrence of at least three distinct isozymes in muscle tissue, providing further evidence for tissue specific expression of GST isozymes in humans.

A novel dinitrophenylglutathione-stimulated ATPase is present in human erythrocyte membranes

Vesicles prepared from human erythrocyte membranes were found to catalyze ATP hydrolysis that was stimulated by dinitrophenylglutathione (Dnp-SG). This activity was dependent on temperature and Mg2+ and independent of ion pump ATPases present in erythrocyte membranes. The activity was a linear function of protein and time up to 60 min. The Km values of ATPase for Dnp-SG and ATP were found to be 49 microM and 1.67 mM, respectively. This suggests that in erythrocytes, the transport of Dnp-SG requires direct enzymatic hydrolysis of ATP and both Dnp-SG-stimulated ATPase activity and the ATP-dependent efflux of Dnp-SG from erythrocytes represent different activities of the same protein.

Expression of glutathione S-transferase isoenzymes in human small cell lung cancer cell lines

A glutathione S-transferase (GST) isoenzyme having common antigenicity to rat placental form (GST-P) and human placental form (GST-pi) has recently been suggested may be a marker of carcinogenesis. In the present study we have investigated the expression of this isoenzyme in three small cell lung cancer cell lines in order to determine whether or not this isoenzyme can be used as a general marker of carcinogenesis. GST activity towards 1-chloro-2,4-dinitrobenzene in two of the cell lines (NES and NOC-361) was moderately higher than that in normal human lung, but this activity was markedly suppressed in one of the cell lines (NCI-H69). Quantitation of the GST isoenzymes in the tumors grown in nude mice by injecting these cell lines also revealed a moderate increase of GST-pi-type isoenzyme in NES and NOC-361 and its suppression in NCI-H69. Immunocytochemical localization studies with these tumors using antibodies raised against GST-pi also indicated a drastic decrease of GST-pi-type isoenzyme in NCI-H69 and this finding was confirmed by Western blot studies. These results suggest that GST-pi, or the isoenzyme(s) having similar immunological nature to GST-pi, cannot be used as the general markers of neoplastic states.

Immunocytochemical evidence for the expression of GST1, GST2, and GST3 gene loci for glutathione S-transferase in human lung

Immunocytochemical studies demonstrate that significant amounts of glutathione S-transferase (GST) are associated with alveoli and bronchioles of human lung. The immunofluorescence in human lung sections was observed with the antibodies which were raised against GST psi and GST alpha-epsilon of human liver and GST pi of human placenta indicating that the isoenzymes corresponding to three gene loci, GST1, GST2, and GST3 are present in human lung. Presence of GST isoenzymes in significant amounts in bronchioles and alveoli of human lung indicate that these isoenzymes may play an important role in the detoxification of xenobiotics as well as in combating oxidative stress through glutathione peroxidase II activity.

A Coomassie blue-binding assay for the microquantitation of immobilized proteins

A sensitive assay procedure for the determination of microgram quantities of immobilized proteins is described. The procedure is based on the property of Coomassie blue G-250 to bind strongly yet reversibly to proteins. The assay involves incubation of the immobilized protein with a solution containing 0.1% Coomassie blue, 10% acetic acid, and 25% isopropyl alcohol in distilled water at room temperature followed by washing off of the unbound dye. The protein-bound dye is eluted with methanolic NaOH, acidified, and the absorbance is measured at 605 nm. The assay is highly reproducible and several proteins immobilized on various matrices could be conveniently assayed. Protein values determined by the dye-binding assay showed good agreement with those obtained by other procedures.

Bromophenol blue protein assay: improvement in buffer tolerance and adaptation for the measurement of proteolytic activity

A modification of the bromophenol blue dye binding procedure of protein estimation is described. Substitution of glycine/phosphoric acid, pH 2.6, for dilute acetic acid in the colour reagent extended the applicability of the procedure to protein solutions containing buffers of various pH values. This was, however, accompanied by approximately 25% loss in the sensitivity of the procedure. The modified reagent exhibited very marked tolerance to detergents and could be successfully adapted for the measurement of proteolytic activity in acidic, neutral or alkaline pH ranges.

Studies on the migratory route of Paragonimus siamensis in the bandicoot (Bandicota indica)

The migration route and the development of P. siamensis obtained from S. juliae and S. germaini were studied in B. indica. The infection rates of P. siamensis in these 2 species of crabs were 19.7% and 21.4% respectively. Worms were recovered in the abdominal cavity, pleural cavity and lungs on day 12, 16 and 30 respectively after oral infection. Worms became mature and laid eggs on day 47 after infection, but their size still increased considerably. The average egg output was found to be 144 eggs/gm faeces/worm or 443 eggs/day/worm. The average recovery rate of P. siamensis in the experimental B. indica was 15%.