Studies on the variability of glutathione S-transferase from human erythrocytes

Understanding quasi-apoptosis of the most numerous enucleated components of blood needs detailed molecular autopsy

Erythrocytes are the most numerous cells in human body and their function of oxygen transport is pivotal to human physiology. However, being enucleated, they are often referred to as a sac of molecules and their cellularity is challenged. Interestingly, their programmed death stands a testimony to their cell-hood. They are capable of self-execution after a defined life span by both cell-specific mechanism and that resembling the cytoplasmic events in apoptosis of nucleated cells. Since the execution process lacks the nuclear and mitochondrial events in apoptosis, it has been referred to as quasi-apoptosis or eryptosis. Several studies on molecular mechanisms underlying death of erythrocytes have been reported. The data has generated a non-cohesive sketch of the process. The lacunae in the present knowledge need to be filled to gain deeper insight into the mechanism of physiological ageing and death of erythrocytes, as well as the effect of age of organism on RBCs survival. This would entail how the most numerous cells in the human body die and enable a better understanding of signaling mechanisms of their senescence and premature eryptosis observed in individuals of advanced age.

Glutathione depletion in human erythrocytes and rat liver: a study on the interplay between bioactivation and inactivation functions of liver and blood

The interplay between bioactivation and inactivation functions of human erythrocytes and rat liver was studied. Glutathione depletion was used as a measure of the amount of reduced glutathione (GSH)-reactive compound. Iodoacetamide (IAcA), N-ethylmaleimide (NEM) and diethyl maleate (DEM), which are electrophiles that need no metabolic activation, were able to deplete GSH in incubations with either aqueous GSH solution or erythrocytes. These results indicate that these compounds can pass the erythrocyte membrane. Cyclophosphamide (CP), 3-hydroxyacetanilide (3-HAA) and 2-methylfurane (2-MF) needed metabolic activation by rat liver microsomes to deplete glutathione in incubations with aqueous GSH solution or erythrocytes. By measuring the sum of both reduced and oxidized glutathione [ = total glutathione (GT)] it became clear that GSH-reactive metabolites are generated out of CP, 3-HAA and 2-MF by the action of microsomes and that these metabolites can pass through the erythrocyte membrane. As GT depletion was higher when microsomes of phenobarbital-pretreated rats were used, the metabolites were (are expected to be) generated by phenobarbital-inducible enzymes. GT was also depleted in incubations with haemolysate and 3-HAA or 2-MF but not in incubations with aqueous GSH solution, which indicates that erythrocyte cytosol can metabolize 3-HAA and 2-MF into GSH-reactive compounds. The pesticides monuron and monulinuron did not affect GT concentrations when aqueous GSH solution, haemolysate or erythrocytes with or without microsomal activating system were tested. When hepatocytes were incubated with 3-HAA or CP (2 mm), about 2 mm of internal GT concentration was depleted. The hepatocytes excreted GSH-reactive metabolites generated from 3-HAA and CP (about 20% of the metabolites formed for 3-HAA). Erythrocyte GT was not depleted in co-incubations of hepatocytes and erythrocytes with 3-HAA. This can be explained by the amounts of GSH-reactive metabolites excreted by the hepatocytes, which would require very effective uptake by the erythrocytes in order to be detectable.

Red blood cell subpopulations in freshly drawn blood: application of proteomics and metabolomics to a decades-long biological issue

BACKGROUND

It has long been known that red blood cells comprise various subpopulations, which can be separated through Percoll density gradients.

MATERIALS AND METHODS

In this study, we performed integrated flow cytometry, proteomic and metabolomic analyses on five distinct red blood cell subpopulations obtained by Percoll density gradient separation of freshly drawn leucocyte-depleted erythrocyte concentrates. The relation of density gradient fractions to cell age was confirmed through band 4.1a/4.1b assays.

RESULTS

We observed a decrease in size and increase in cell rugosity in older (denser) populations. Metabolomic analysis of fraction 5 (the oldest population) showed a decrease of glycolytic metabolism and of anti-oxidant defence-related mechanisms, resulting in decreased activation of the pentose phosphate pathway, less accumulation of NADPH and reduced glutathione and increased levels of oxidized glutathione. These observations strengthen conclusions about the role of oxidative stress in erythrocyte ageing in vivo, in analogy with results of recent in vitro studies. On the other hand, no substantial proteomic differences were observed among fractions. This result was partly explained by intrinsic technical limitations of the two-dimensional gel electrophoresis approach and the probable clearance from the bloodstream of erythrocytes with membrane protein alterations. Since this clearance effect is not present in vitro (in blood bank conditions), proteomic studies have shown substantial membrane lesions in ageing red blood cells in vitro.

CONCLUSION

This analysis shows that the three main red blood cell subpopulations, accounting for over 92% of the total RBC, are rather homogeneous soon after withdrawal. Major age-related alterations in vivo probably affect enzyme activities through post-translational mechanisms rather than through changes in the overall proteomic profile of RBC.

Pyruvate kinase is protected by glutathione-dependent redox balance in human red blood cells exposed to reactive oxygen species

To determine the antioxidant role of glutathione (GSH) in human red blood cells (RBCs), we investigated the effect of disrupting GSH homeostasis on the oxidative modification of thiol-dependent enzymes by exposure to tert-butyl hydroperoxide (BHP). When hemolysate was incubated with BHP, significant decreases in enzyme activity were observed. However, the inactivation did not occur in intact RBC suspensions that were exposed to BHP. In this study, we used two independent treatments aimed at decreasing the level of reduced form of GSH, pre-incubation with a glutathione reductase inhibitor or glucose-free medium to examine the influences of preventing GSH-dependent antioxidant and reactivation activity on thiol-dependent enzyme. Pyruvate kinase (PK) activity clearly decreased along with depletion of GSH compared to other glycolytic enzyme activities by BHP exposure in RBCs. The addition of GSH, but not glucose, before BHP exposure completely prevented the inactivation of PK in hemolysate; however, partial reactivation of inactivated PK was observed by post-addition of both GSH and glutaredoxin at an early stage during BHP exposure. Moreover, hydroxyl radicals but not hydrogen peroxide inactivated PK. These results suggest that PK is highly susceptible to radicals and that GSH is essential to protect PK activity by not only directly scavenging radicals but also by systematically reactivating oxidized enzyme in human RBCs.

The use of glutathione transferase-knockout mice as pharmacological and toxicological models

ADME/Tox studies are of increasing importance because of the necessity to eliminate poor drug candidates early in the development pipeline. The glutathione S-transferases (GSTs) are a family of phase II enzymes that have been shown to play a significant role in the disposition of a wide range of drugs and other xenobiotics. Several GST-knockout mice strains have been developed that can potentially be used in ADME/Tox studies. So far, mice have been generated with deficiencies of mGSTP1/2, mGSTA4-4, mGSTZ1-1, mGSTM1-1, mGSTO1-1 and mGSTS1-1, but studies of drug metabolism in these strains have been limited. As there are 21 recognised GST genes in mice there is potential for many more strains to be made. However, a review of the available data suggests that because of differences in the evolution of the GST gene family between rodents and humans, only some knockout strains can provide insights relevant to human drug metabolism. It is concluded that, of the strains generated so far, only those deficient in mGSTP1-1, mGSTA4-4, mGSTO1-1 and mGSTZ1-1 have direct human orthologues and can be considered as human models. In contrast, there may not be appropriate orthologues of some enzymes, such as hGSTM1-1, that are known to be of relevance in drug metabolism.

Contributions of the sympathetic nervous system, glutathione, body mass and gender to blood pressure increase with normal aging: influence of heredity

Body mass and sympathetic activity increase with aging and might underlie blood pressure (BP) elevation. Increased body mass index (BMI) may elevate BP by increasing sympathetic activity. Glutathione (GSH) can decrease BP, and declines with aging. We measured systolic (SBP) and diastolic BP, BMI, plasma (NE(pl)) and urine norepinephrine (NEu), and plasma GSH in n=204 twins across the age spectrum. BP correlated directly with BMI, NEpl, and NEu, but inversely with GSH. Age correlated with BP, BMI, NEpl, and NEu. BP, BMI, NEpl, and NEu were higher in older subjects than younger subjects, whereas GSH was lower with aging. In older subjects with high (above median) NEpl, SBP was 8 mmHg higher than in those of comparable age with low NE. In younger subjects with high GSH, BP was significantly lower than in younger subjects having low GSH. NEu was significantly reduced in young high-BMI subjects vs young low-BMI subjects. The heritability (h2) of NEpl, NEu, and GSH ranged from approximately 50 to approximately 70%, and these biochemical quantities were considerably more heritable than BP. We conclude that increases in sympathetic activity contribute to aging-induced SBP elevations, especially in older females. GSH reductions apparently participate in aging-induced BP elevations, most strongly in males. BMI increases contribute to BP elevations, particularly in younger subjects. BMI elevations apparently raise BP mainly by peripheral mechanisms, with generally little sympathetic activation. Substantial h(2) for plasma GSH, NE, and urine NE suggests that such traits may be useful 'intermediate phenotypes' in the search for genetic determinants of BP.

Age and gender dependent alterations in the activities of glutathione related enzymes in healthy subjects

OBJECTIVES

Oxidative stress as a result of increased free radical production is implicated in the pathogenesis of several diseases. Specific antioxidant enzymes have a crucial role in the prevention of these deleterious effects. Since the activities of these enzymes differ significantly in different populations and seem to be affected by various environmental factors, in this study we aimed to determine the reference values of glutathione related antioxidant enzyme activities in the erythrocytes of healthy subjects and to investigate the possible variations as a function of age and gender in a healthy Turkish Mediterranean population.

DESIGN AND METHODS

130 healthy subjects (12-90 yr, 82 females, 48 males) were divided into six different age groups. Erythrocyte glutathione peroxidase (GSH-PX), glutathione reductase (GR) and glutathione-s-transferase (GST) activities were measured on a Hitachi 704 autoanalyser by the modification of previously described manual UV spectrophotometric methods.

RESULTS

No significant differences were observed in erythrocyte GSH-PX, GR and GST activities between different age groups. Overall, GST activities were significantly higher in females compared with males (8.08 +/- 1.39, 6.88 +/- 1.51 U/g Hb respectively, mean +/- SD, p < 0.001). A significant positive correlation between GSH-PX and GR activities was observed (r = 0.49, p < 0.001).

CONCLUSION

The results of this study suggested that the activities of GSH-PX, GR and GST did not depend. GST activities overall were higher in females. The reference values that we obtained were different than the previous reports. This situation implies that each population should determine its own reference values and should investigate the influence of environmental factors and life style habits on the activities of these enzymes that constitute a major part of the antioxidant defense system in the human organism.

Genetic heterogeneity of the structure and function of GSTT2 and GSTP1

In this study new methods for the detection of two polymorphic sites in the GSTP1 coding region have been developed. Both sites are polymorphic in several racial groups and there are significant differences between groups, in the gene frequency at each site. Although previous studies of recombinant GSTP1-1 have suggested that there are significant differences in the specific activity and stability of the I105 or V105 isoforms, no differences in the distribution of GSTP1-1 activities in normal blood donors with different GSTP1 genotypes were detected in this study. These data were obtained with CDNB as a substrate and greater differences may be apparent with different substrates. The structure and organization of the GSTT2 gene was also investigated and a pseudogene that occurs at a polymorphic frequency in European Australians was discovered. This pseudogene can be detected by PCR/RFLP analysis.

Modifications of glutathione S-transferase (GST) activity in the last period of pregnancy in rats treated with benzo(a)pyrene (BP)

Pregnant rats were treated with benzo(a)pyrene (BP) (50 mg/kg every 2 days) from day 7 of pregnancy and killed at day 16 or day 19. Km of erythrocyte glutathione S-transferase (GST) decreased during pregnancy in control rats (1.29 x 10(-3) M at day 16; 1.02 x 10(-3) M at day 19) and even more in treated rats at day 19 (0.71 x 10(-3) M). Vmax was lower in treated rats at day 19 (0.56 mumol/min/g haemoglobin) than in control rats (0.88 mumol/min/g haemoglobin) suggesting inhibition of the enzyme. Placental weight diminished in treated rats at day 19 but was not affected at day 16. Chromatofocusing of placental GST showed a single peak (pH 8.3-8.6) in control and treated rats on day 16 and an additional peak (pH 7.0-7.4) in treated rats on day 19. An increase in Km (2.84 x 10(-3) M) and Vmax (69 nmol/min/mg protein) in placental GST was observed in treated rats at day 16 (Km = 1.61 x 10(-3) M; Vmax = 43.3 nmol/min/mg protein, in control rats) followed by a decrease in these parameters in rats treated until day 19 (Km = 1.63 x 10(-3) M; Vmax = 48.7 nmol/min/mg protein). These results suggest that BP, initially, stimulates GST synthesis in placenta, followed by an inhibition of the enzyme at day 19. Fetal weight was also affected by BP treatment, especially at day 16. Km and Vmax values of fetal GST were higher in treated rats at day 16 than in control rats but these differences were not detectable at day 19. This may be explained by the more protective role of the placenta at day 19 than at day 16. Glutathione content in erythrocytes, placenta and fetus was not affected by BP.

Enhanced glutathione S-transferase (GST) activity in pregnant rats treated with benzo(a)pyrene

Administration of Benzo(a)pyrene (BP, 50 mg/kg/d) to pregnant rats significantly increased Glutathione S-transferase (GST) activity in placental tissue-extract (Vmax = 40 nmol/min/mg protein and 69 nmol/min/mg protein in controls versus treated animals respectively; P less than 0.01) and total fetal tissue-extract (Vmax = 51 nmol/min/mg protein and 82 nmol/min/mg protein in controls versus treated animals respectively; P less than 0.01) indicating an induction effect of BP on the GST system. An increase in the Km values was also observed: 1.61 x 10(-3) M and 2.84 x 10(-3) M in control versus treated placentae; 1.38 x 10(-3) M and 2.05 x 10(-3) M in control versus treated fetuses. A competitive effect on the enzyme by the BP present in the sample may also be involved. The glutathione content in both tissues did not show any changes after the treatment with BP. This increase in the GST system was not sufficient to protect the fetus. BP affected the reproductive performance of pregnant rats by significantly increasing the number of resorptions and fetal wastage, and, also, by decreasing the fetal weight.

Cell age dependent decay of human erythrocytes glutathione S-transferase

Human red blood cells contain both glutathione S-transferase sigma (GST sigma) and glutathione S-transferase rho (GST rho). While the first isozyme does not change in red blood cell fractions of different mean density (age), GST rho, the main isozyme, shows a pronounced cell age dependent decay. Ion-exchange chromatographic experiments show that GST rho consists of only one isozymic form in young erythrocytes but is present in two components, with different electric charge, in mature and old cells. The "secondary" GST rho isozyme is more heat stable than the "primary" GST rho isozyme with the result that the total GST activity shows an apparent increase in heat stability during cell aging due to the formation of "secondary" isozymes. The kinetic properties and specificity of this enzyme do not show appreciable modifications during cell ageing. The data reported in this paper suggest that red blood cell aging is associated with a reduced detoxifying ability due to GST rho decay.

Biological effect monitoring of occupational exposure to 1,3-dichloropropene: effects on liver and renal function and on glutathione conjugation

A prospective study was performed in the Dutch flower bulb culture to investigate the possible effects of subchronic exposure to the soil fumigant 1,3-dichloropropene (DCP) on liver and kidney function and on glutathione conjugation capacity in blood. Urine spot samples and venous blood samples from 14 workers applying DCP (applicators) were taken at the start of the season in July, and after the season in October. The parameters of liver function measured were: alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, gamma-glutamyltranspeptidase, and total bilirubin (conjugated and unconjugated). Total bilirubin was significantly decreased from 9.5 before to 7.0 mumol/l after the season. In combination with an increase in serum gamma-glutamyltranspeptidase activity from 12.5 to 19.5 U/l this indicates moderate hepatic enzyme induction. To study renal function, creatinine and beta 2-microglobulin in serum, and beta 2-microglobulin, albumin, alanine aminopeptidase, beta-galactosidase, and retinol binding protein in urine were measured. The glomerular function parameters albumin in urine and creatinine in serum changed significantly during the season: albumin concentration increased from 5.2 to 7.6 mg/l, whereas creatinine concentration [corrected] decreased from 93.0 to 87.5 mumol/l. The tubular function parameter retinol binding protein also increased in concentration from 20.0 to 26.9 micrograms/l. Therefore, a subclinical nephrotoxic effect of subchronic exposure to DCP cannot be excluded. Effects on glutathione conjugation capacity were studied by measuring erythrocyte glutathione S-transferase activity and blood glutathione concentrations. The activity of glutathione S-transferase in erythrocytes was significantly decreased from 4.7 before to 3.3 U/g haemoglobin after the season. The same was true for the blood glutathione concentrations, which decreased from 0.93 to 0.82 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of ethylene oxide in human blood and its implications for biomonitoring

The distribution of radioactivity following the incubation of human blood with radio-labelled ethylene oxide was investigated in vitro. After incubation, the individual blood samples were separated into lymphocytes and high (Mr greater than 10,000) and low (Mr less than 10,000) molecular fractions of erythrocyte cytoplasm and blood plasma. The radioactivity was determined in each sample by liquid scintillation counting. In erythrocyte cytoplasm, the distribution of radioactivity showed marked interindividual differences and two distinct groups could be distinguished. The coincidence of these groups with 'conjugators' and 'non-conjugators', in terms of the enzymatic conjugation of methyl halides to glutathione in erythrocytes, suggests a common principle, such as enzyme polymorphism. Such polymorphism has been described for glutathione S-transferase mu in the human liver, an enzyme that efficiently conjugates epoxides. In the other blood compartments, the interindividual differences were either less significant or were not detectable. Binding products with various macromolecules in blood, such as haemoglobin or lymphocyte DNA, are being discussed as biological monitors for occupational exposure to ethylene oxide. The observation that erythrocytes exhibit interindividual differences as described above make binding products with haemoglobin less suitable for biological monitoring of ethylene oxide exposure than, for example, DNA adducts in lymphocytes.

Glutathione-S-transferase activity in human superficial transitional cell carcinoma of the bladder. Comparison with healthy controls

Glutathione-S-transferase (GST) activity and glutathione (GSH) content have been studied in human urinary bladder (UB) specimens obtained from healthy controls (HC) (n = 8) and from patients with superficial transitional cell carcinoma (TCC) (n = 9), either in TCC and in adjacent normal (ANE) tissues of the same patient. The GST activity was significantly higher in TCC in comparison with ANE (ten fold) and with HC (five fold). This activity was also significantly higher in HC than in ANE (two fold). The Km values obtained in the whole population (1.26 +/- 0.3 X 10(-3) mol/l) suggest that a unique form of isoenzyme is present in the UB epithelium and that it is the same acidic form "rho" described in erythrocytes. The GSH content was significantly higher in TCC than in ANE (2.5 fold) and also that in HC (three fold). A good correlation between GST activity and GSH content was observed in HC but not in TCC or ANE. These results demonstrate the relation between the activity of the GST system and the development of the TCC as well as its role in the cellular resistance to chemotherapy. A possible decrease of the GST activity before the development of the tumor is also discussed.

A comparative investigation of the metabolism of methyl bromide and methyl iodide in human erythrocytes

Human erythrocyte cytoplasm was incubated in head space vials with either methyl bromide or methyl iodide. The decline in concentration of the two methyl halides was monitored by gas chromatography. Simultaneously, the production of S-methylglutathione was determined by thin layer chromatography. In parallel experiments, boiled erythrocyte cytoplasm was used in order to determine non-enzymatic conjugation. Furthermore, inhibition experiments with sulfobromophthalein were performed. The results were compared with previous findings on the metabolism of methyl chloride. In contrast to methyl chloride, both methyl bromide and methyl iodide showed a significant non-enzymatic conjugation with glutathione. In addition, an enzymatic conjugation could be observed in the erythrocyte cytoplasm of the majority of the population, whereas a minority lacks this enzymatic activity. This is consistent with findings on methyl chloride. Inhibition experiments show that a minor form of the erythrocyte glutathione transferase may be responsible for the enzymatic conjugation. Of the three monohalogenated methanes, methyl bromide is the substrate with the highest affinity for the conjugating enzyme(s). In the case of methyl iodide, non-enzymatic reaction overweighs the enzymatic process. There are possible implications of the results for occupational health and the toxicity of the substances.

Genetic heterogeneity of the human glutathione transferases: a complex of gene families

The glutathione transferases (GSTs) are involved in the metabolism of a wide range of compounds of both exogenous and endogenous origin. There is evidence that deficiency of GST may increase sensitivity to certain environmentally derived carcinogens. In contrast, elevated expression has been implicated in resistance to therapeutic drugs. The GSTs are the products of several gene families. This review summarizes the present knowledge of the genetic interrelationships between the various isoenzymes, their deficiencies and the physical locations of their genes.

Metabolism of methyl chloride by human erythrocytes

Erythrocyte cytoplasm of rats, mice and humans was incubated in head space vials with methyl chloride and the decline in concentration of the substance monitored as a parameter of metabolism. The production of S-methylglutathione was controlled by tlc. Rats, mice, bovines, pigs, sheep and rhesus monkeys showed no conversion of methyl chloride in erythrocyte cytoplasm. About 60% of the human blood samples showed a significant metabolic elimination of the substance (conjugators), whereas about 40% did not (non-conjugators). The production of S-methylglutathione indicated enzymatic metabolism of the substance by glutathione S-transferases. In literature, a "major" and "minor" form of human erythrocyte glutathione S-transferase has been described. The results indicate that the "minor" form is probably responsible for the unique metabolism of methyl chloride in human erythrocytes.

The human glutathione S-transferase. Studies on the kinetic, stability and inhibition characteristics of the erythrocyte enzyme

Bromosulphophthalein and N-ethylmaleimide, inhibitors of glutathione S-transferase (EC 2.5.1.18 RX: glutathione R. transferase), have been used to identify variant forms of the erythrocyte enzyme. One 'atypical' sample was detected and was shown to have appreciably different kinetic and stability properties. These inhibitors may be useful in surveys of variation in this group of enzymes.

Glutathione metabolizing enzyme activities in human thyroid

Glutathione peroxidases, glutathione transferase, glutathione reductase and gamma-glutamyl transpeptidase activities were analyzed in human thyroid tissues obtained from 17 patients undergoing resectional surgery because of a malignancy. It was deduced, from measurements of glutathione peroxidase activity with both H202 and cumene hydroperoxide, that thyroid contains only the selenium enzyme. The absence of selenium independent glutathione peroxidase activity in thyroid was confirmed with gel filtration experiments. An interindividual variation of about 28-fold was found measuring glutathione transferase activity with 1-chloro-2,4-dinitrobenzene. Subjecting a fraction of human thyroid cytosols partially purified by G-100 Sephadex column to isoelectricfocusing run, a single peak of glutathione transferase activity centered at pH 4.6 was obtained. An adequate level of glutathione reductase and gamma-glutamyl transpeptidase activities was also found in all specimens investigated.

Studies of the development of basic, neutral and acidic isoenzymes of glutathione S-transferase in human liver, adrenal, kidney and spleen

The ontogeny of basic, near-neutral and acidic glutathione S-transferase isoenzymes was studied by using chromatofocusing and ion-exchange chromatography. These isoenzyme sets demonstrated tissue-specific patterns of expression. For example, whereas basic isoenzymes were identified in all liver and adrenal cytosols obtained after 10 weeks gestation, these forms were not detected in kidney until 10 weeks post-natal age and in spleen until about 40 weeks post-natal age. Our data indicate that the basic monomers B1 and B2 are present in liver cytosol at 21 weeks gestation. Expression of the near-neutral isoenzymes was usually weak; for example, they were not generally expressed in liver until 30 weeks gestation, and no developmental patterns in their expression could be identified in adrenal, kidney and spleen. The acidic isoenzymes were usually strongly expressed in adrenal, kidney and spleen, although there was a decline in the level of expression in kidney after birth.

Purification and characterization of a new form of glutathione S-transferase from human erythrocytes

Presence of a new form of glutathione S-transferase has been demonstrated in human erythrocytes. Using two different affinity ligands this enzyme has been separated from the previously characterized glutathione S-transferases rho. The new enzyme is highly basic with a pI of greater than 10. The new enzyme which represents less than 5 percent of glutathione-S-transferase activity towards 1-chloro-2,4-dinitrobenzene as substrate and about 10 percent of total glutathione S-transferase protein of erythrocytes has different amino acid composition, substrate specificities, and immunological characteristics from those of the major erythrocyte glutathione S-transferase rho. Immunological properties of the new enzyme indicate that this form may be different from other glutathione S-transferases of human tissues.

Studies on the glutathione S-transferase of human platelets

The glutathione S-transferases of human platelets have been compared with those of erythrocytes. Although wide variations in activity were found, in individual subjects, the activity in these cell types was significantly correlated. The enzymes demonstrated similar isoelectric points and electrophoretic mobilities and it appears that the platelet enzyme is also a product of the GST3 locus. There was no correlation between platelet enzyme activity and plasma concentrations of retinol and cholesterol, but in men, the relationship between activity and carotene was significant. It is suggested that GST3 isoenzyme activity depends on vitamin A.

Decreased erythrocyte glutathione s-transferase activity in rubber workers

Decreased erythrocyte glutathione s-transferase activity was found in workers exposed to hot rubber fumes in two-roll mill and calender departments (6.6 +/- 0.9 and 6.8 +/- 0.8 mumol/min X mg haemoglobin, respectively vs 8.4 +/- 0.5 in controls). This trend was also noted in the general category of all rubber exposed workers without stratification according to their task (7.6 +/- 0.5, n = 30). This result was contrary to that expected, as the cases with the lowest values had the greatest urinary thioether excretion. The thioethers are the end-products of the enzyme-catalyzed glutathione conjugation reaction aimed at the inactivation of potentially toxic chemicals. Thus, it appears that the assay of erythrocyte glutathione s-transferase activity is not very informative about exposure, although the enzyme assay might disclose other, so far unknown, biological effects of reactive rubber chemicals.

Erythrocyte glutathione S-transferase. Electrophoretic identification of two enzyme forms

Starch-gel electrophoresis was used to demonstrate two forms of glutathione S-transferase in human erythrocytes. Whereas considerable inter-individual differences in enzyme activity and electrophoretic patterns were detected, intra-individual differences were small.