Biomedical subjects

N Q Li

Publications and source records attributed to N Q Li.

At least 19 recordsLinked to original sources

PubMed2001

The direct electrochemistry of myoglobin at a DL-homocysteine self-assembled gold electrode.

A pair of well-defined redox waves of myoglobin at a DL-homocysteine self-assembled gold electrode was achieved. Myoglobin can strongly bind to the homocysteine self-assembled gold electrode, so the Mb-Hcy self-assembled gold electrode was prepared and the standard rate constant (ks) of Mb was calculated as 9.3 x 10(-1) s(-1). X-ray photoelectron spectroscopy (XPS) measurements demonstrated that Hcy monolayer was formed and Mb was bound to Hcy monolayer.

Animals↗

PubMed2000

Electrochemical study of the effect of ADP and AMP on the kinetics of glutamate dehydrogenase.

A chronoamperometric method based on the 'diffusion' layer concept of the convective system was used to assay the glutamate dehydrogenase (GLDH) activity. Once the reaction was initiated by adding the enzyme GLDH into a well-stirred nicotinamide adenine dinucleotide (NADH, coenzyme) solution, the steady-state oxidation limiting current of NADH would decrease linearly in a short time. The major advantage of this method is that it directly indicates the continuous in-situ change of the coenzyme concentration, thus, the real initial reaction rate of enzyme-catalyzed reaction, V0, can be determined. Using this method, the effect of adenosine-5'-monophosphate (AMP) and adenosine-5'-diphosphate (ADP) on the GLDH activity has been monitored. The results showed that ADP and AMP could increase the activity of GLDH. This activation mechanism was proposed by the voltammetric study.

Adenosine Diphosphate↗

PubMed2000

Electrochemical studies of the interaction of adriamycin to DNA.

An electrochemical investigation of the interaction of adriamycin (DXH) with DNA on a Hg electrode is reported. In weakly acidic media of pH 4.0-7.0, the addition of DNA to DXH solution results in the decrease of redox peak currents. In the presence of DNA, no new peak appears and the standard rate constant k(s) is not significantly changed. The binding of DXH to DNA by electrostatic attraction and intercalation forms a kind of supramolecular complex DXH-DNA, which is electrochemically non-active. The equilibrium constant for the complex is calculated. The decrease in peak current is proportional to DNA concentration and can be used to determine DNA concentration.

Antibiotics, Antineoplastic↗

PubMed2000

Variations in dietary iron alter brain iron metabolism in developing rats.

The rat has been widely used as a model for the study of iron deficiency (ID), but the differences in the timing of development of humans and rats must be taken into account to derive appropriate conclusions from the animal model. This study was designed to evaluate the effects of dietary ID and iron excess on rat brain iron and the iron metabolism proteins, transferrin (Tf), transferrin receptor (TfR) and ferritin. The experimental design is developmentally sensitive and permits control of the timing as well as the duration of the nutritional insult. Iron-deficient and iron-supplemented (SU) rats between postnatal day (PND) 10 and 21, PND 21 and 35 and PND 10 and 35 were used to study the effects of early, late, and long-term iron deficiency and supplementation. Some ID rats were iron repleted between PND 21 and 35. These experiments demonstrated several new findings: 1) Early ID/SU (PND 10-21) altered brain iron, TfR, Tf and ferritin concentration in many regions different from those observed in the later period (PND 21-35). 2) Two weeks of iron repletion were adequate for correcting the overall Fe concentration of the brain and of individual brain regions, although larger amounts of iron were necessary to fully normalize iron and its regulatory proteins. 3) Long-term ID/SU resulted accordingly in the continued decrease or increase in brain iron concentration in some brain regions and not others. In conclusion, brain regions regulate their iron concentration in response to local needs when faced with alterations in systemic iron delivery.

Animals↗

PubMed2000

Iron status and stores decline with age in Lewis rats.

In the context of a larger study examining the interaction of vitamin A (VA) status and age on immune function, we examined age-related changes in hematologic and iron status variables in male Lewis rats. Animals were fed a nutritionally adequate purified diet containing either 0.35 (marginal), 4.0 (control) or 50 (supplemented) mg retinol equivalents (as retinyl palmitate) per kg of diet from the time of weaning until killing at 8-10 (middle-aged) or 20-22 (old) mo of age. Neither VA nor VA and age interaction effects were significant for most iron variables examined. After controlling for body weight, old rats had significantly lower hemoglobin, hematocrit and plasma iron than middle-aged rats. This decrease in hematologic and transport iron variables was not accompanied by a shift of iron into other storage compartments. Old rats also had significantly lower total iron content and iron concentration in liver, spleen and bone marrow. Hemosiderin iron in marrow smears correlated significantly (r = 0.43-0.76, P: < 0.05) with chemical estimates of iron in storage, transport and functional pools. Old rats also tended to have less stained iron in femur marrow smears. Thus, body iron in functional, transport and storage compartments, namely the liver, spleen and bone marrow, were significantly lower in old than in middle-aged rats. Although iron stores and status are usually considered to increase with advancing age, our data show a consistent pattern of lower hematologic and storage iron variables in old than in middle-aged Lewis rats. Future research is indicated to understand the biology and functional consequences of the observed age-associated decline in body iron.

Aging↗

PubMed1999

Chronic marginal vitamin A status reduces natural killer cell number and function in aging Lewis rats.

Natural killer (NK) cells function in the regulation of immune responses and in the surveillance of malignant or other abnormal cells. Little is known of the effects of chronic marginal vitamin A (VA) status or VA supplementation, or their interaction with age, on NK cell number and cytolytic activity. We have conducted a two-factor (diet, age) study in which male Lewis rats were fed AIN-93M diet, modified to contain either 0.3 (designated marginal), 4.0 (control) or 50 (supplemented) mg retinol equivalents (RE)/kg diet, from the time of weaning until the ages of 2.5 mo (young), 8-10 mo (middle-aged) or 18-20 mo (old). Natural killer cells were identified and quantified in peripheral blood mononuclear cells (PBMC) and spleen with the use of flow cytometry, and NK cell cytotoxicity was assayed. The number and percentage of PBMC NK cells increased with age (P < 0.0001 by two-way ANOVA). For all age groups, values were lowest in rats with marginal VA status (P < 0.0001 vs. controls). NK cell lytic activity also declined with age (P = 0. 0003). As a result, NK cell lytic efficiency (lytic activity per NK cell) decreased markedly with age (P < 0.0001). Regardless of the donor's age or VA status, PBMC NK cell cytotoxicity doubled (100 +/- 25% increase) after exposure to interferon-alpha (5 x 10(5) U/L for 1 h before assay), indicating that IFN-stimulated lytic activity was related directly to basal NK cell activity. If the relationships observed in this animal model can be applied to humans, these data suggest that elderly people consuming diets chronically low in VA may be at increased risk for infectious or neoplastic diseases.

Aging↗

PubMed1993

Pulsatile and steady flow induces c-fos expression in human endothelial cells.

The effects of pulsatile and steady fluid flow on the mRNA levels of proto-oncogenes c-fos, c-jun, and c-myc in cultured human umbilical vein endothelial cells (HUVEC) were investigated. c-fos mRNA levels in stationary cultures were very low. A 1 Hz pulsatile flow with an average shear stress of 16 dynes/cm2 induced a dramatic increase of c-fos mRNA levels in HUVEC 0.5 h after the onset of flow, which declined rapidly to basal levels within 1 h. Steady flow with a similar shear stress also induced a transient increase of c-fos mRNA levels, but to a lesser extent. In addition, increased c-fos mRNA levels were observed when low shear (2-6 dynes/cm2) was replaced by high shear (16-33 dynes/cm2). Pulsatile and steady flow caused a slight increase of c-jun and c-myc mRNA levels. The role of pulsatility was also investigated in platelet-derived growth factor (PDGF) expression. Pulsatile flow induced a transient increase of PDGF A- and B-chain mRNA levels with peaks at 1.5-2 h. Pulsatile flow, which was more stimulatory in mediating c-fos expression, however, was less stimulatory than steady flow in mediating PDGF expression. By using various inhibitors, protein kinase C was found to be an important mediator in flow-induced c-fos expression, with the involvement of G proteins, phospholipase C, and intracellular calcium. Protein kinase C was previously shown as a possible major mediator in flow-induced PDGF expression which, at least partly, appeared to follow the induction mechanism of c-fos, suggesting a possible connection between c-fos and PDGF induction. However, the c-fos antisense treatment, which significantly inhibited c-fos transcription, failed to block the flow-induced PDGF expression, suggesting that flow-induced c-fos expression may not play an important role in the mechanism of flow-induced PDGF expression. The difference in the induction of c-fos and PDGF expression under pulsatile as compared to steady flow indicates that a complex, flow-mediated regulatory mechanism of gene expression exists in HUVEC. The increased expression of these proto-oncogenes mediated by flow may be important in regulating long-term cellular responses.

Base Sequence↗

PubMed1992

Shear-induced platelet-derived growth factor gene expression in human endothelial cells is mediated by protein kinase C.

Our previous studies have shown that steady shear stress causes a transient increase of platelet-derived growth factor (PDGF) A and B chain mRNA levels in human umbilical vein endothelial cells (HUVEC). In the present study, we elucidated the signaling pathway of shear stress in HUVEC by examining the roles of protein kineses, intracellular calcium, cyclooxygenase, and guanine nucleotide-binding proteins (G proteins) in the PDGF gene induction by shear. The protein kinase C inhibitors, H7 and staurosporine, strongly inhibited the shear-induced PDGF gene expression in HUVEC. In contrast, HA1004, a cAMP- and cGMP-dependent protein kinases inhibitor, was only slightly inhibitory. BAPTA/AM, an intracellular calcium chelator, partially (50%) inhibited the shear-induced PDGF gene expression. The cyclooxygenase inhibitors, ibuprofen and indomethacin, were slightly inhibitory. A 35-50% inhibition of shear-induced PDGF gene expression was found with GDP-beta-S, an inhibitor of G proteins. These results suggest that shear-induced PDGF gene expression in HUVEC is mainly mediated by protein kinase C activation and requires intracellular calcium. Furthermore, G proteins seem to be involved in this process, whereas prostaglandin synthesis via cyclooxygenase pathway is not. We propose a mechanism of shear-induced PDGF gene expression in HUVEC: Shear stress, either directly or indirectly (G protein-mediated), enhances the membrane phosphoinositide turnover via phospholipase C, producing diacylglycerol, an activator of protein kinase C. The activated protein kinase C then triggers the subsequent PDGF gene expression.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1992

[Clinical and experimental study on shen-qi injection with chemotherapy in the treatment of malignant tumor of digestive tract].

Shen-Qi (Ginseng-Astragalus) injection was used with chemotherapy in the treatment of 176 cases of malignant tumor of the digestive tract. Results showed that Shen-Qi injection could reduce the toxic effects produced by chemical agents and increase the patient's body weight, as compared with that treated by chemotherapy alone (P < 0.001). It could protect the body's hematopoietic function. In Shen-Qi injection with chemotherapy group; the WBC count changed insignificantly but in chemotherapy group the WBC count reduced markedly, in which the rate of chemotherapy failure was 26.5% the difference between these two groups appeared to be significant (P < 0.01). Shen-Qi injection could increase the cellular immunologic function of the body, including phagocytic index and percentage of phagocytes, T lymphocyte transformation rate(cpm) as well as esterase stain. Further more, Shen-Qi injection could promote blood circulation to remove blood stasis and reduce the whole blood specific viscosity (P < 0.05). In the animal experiment, the total number of bone marrow cells and karyocytes of combined treatment group was found to be higher (P < 0.001) and the average weight of thymus was heavier (P < 0.05) than that in chemotherapy group. Shen-Qi injection could also prolong the survival time and increase the tumor inhibiting rate of experimental mice.

Adenocarcinoma↗

PubMed1991

Shear stress increases endothelial platelet-derived growth factor mRNA levels.

We have investigated the effect of shear stress on platelet-derived growth factor (PDGF) A and B chain mRNA levels in cultured human umbilical vein endothelial cells (hUVEC). The levels of both PDGF A and B mRNA in hUVEC were increased by a physiological shear stress (16 dyn/cm2), reaching a maximum approximately 1.5-2 h after the onset of shear stress and returning almost to control values at 4 h. The peak levels showed a more than 10-fold enhancement for PDGF A mRNA and a 2- to 3-fold increase for PDGF B mRNA (P less than 0.05). PDGF A mRNA also showed a shear-dependent increase from 0 to 6 dyn/cm2 (P less than 0.05) and then plateaued from 6 to 51 dyn/cm2. PDGF B mRNA levels were elevated as shear stress increased from 0 to 6 dyn/cm2 then declined gradually to a minimum at 31 dyn/cm2 (P less than 0.05) and increased again when shear stress rose to 51 dyn/cm2 (P less than 0.05). PDGF, a potent smooth muscle cell mitogen and vasoconstrictor, released from the endothelium may regulate the blood flow in vivo. The shear stress-dependent elevation of PDGF A and B mRNA in endothelial cells may be involved in the adaptation of blood vessels to flow mediated by the endothelium.

Cells, Cultured↗

PubMed1990

Elevation of rat liver mRNA for selenium-dependent glutathione peroxidase by selenium deficiency.

Selenium-dependent glutathione peroxidase (Se-GSH-Px, GSH-H2O2 oxidoreductase EC 1.11.1.9) is the best characterized selenoprotein in higher animals, but the mechanism whereby selenium becomes incorporated into the enzyme protein remains under investigation. To elucidate the mechanism of insertion of selenium into Ge-GSH-Px further, we have systematically analyzed and compared the results of Western blot, in vitro translation immunoprecipitation, and Northern blot experiments conducted with liver proteins and RNAs obtained from rats fed on selenium-deficient and selenium-supplemented diets. The anti-serum employed in this study was raised against an electrophoretically pure Se-GSH-Px preparation obtained from rat livers by a simplified purification procedure involving separation by high performance liquid chromatography on a hydrophobic interaction column. Different forms of Se-GSH-Px, including apo-protein, cross-reacted with this antiserum and Western blot analysis found no Se-GSH-Px protein present in livers from rats fed on selenium-deficient diets. By contrast, a distinct protein band corresponding to purified Se-GSH-Px was detected in livers from selenium-supplemented animals, a result consistent with the finding that the Se-GSH-Px activity was reduced to undetectable levels in livers of selenium-deficient rats. The in vitro translation experiments, however, indicated not only that mRNA for Se-GSH-Px was present during selenium deficiency but also that its translation products contained 2-3-fold as much immunoprecipitable protein as the products of poly(A) RNA from livers of selenium-supplemented rats. This result suggests that the Se-GSH-Px mRNA may be increased in the selenium-deficient state. Elevated levels of Se-GSH-Px mRNA were directly demonstrated in Northern blot experiments employing cDNA clone pGPX1211 as a probe. A similar increase in Se-GSH-Px mRNA was observed in such other tissues as kidney, testis, brain, and lung tissue, in selenium-deficient states. The present data support the co-translational mechanism for the incorporation of selenium into Se-GSH-Px in rat liver.

Animals↗

PubMed1990

Antibodies directed against the thiomannose moiety of a glycoconjugate of 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside and bovine serum albumin.

Anti-thiomannose antibodies were induced in rabbits immunized with a glycoconjugate of 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside (Man-S) and bovine serum albumin (BSA). Also anti-BSA antibodies directed against the BSA moiety of the glycoconjugate were detected in low concentrations in the immune serum. However, antibodies against the combinatorial epitope of the hapten group and the carrier protein were not detected. The anti-thiomannose and the anti-BSA antibodies were isolated in pure forms by affinity chromatography on Sepharose 4B-bearing thiomannosyl-BSA ligands or BSA ligands. The anti-thiomannose antibodies constituted the major fraction of the antibodies, and these antibodies were isolated in pure form for the first time. The specificity of the thiomannose antibodies was established from data of experiments of periodate oxidation, perpropionic acid oxidation, hapten inhibition, and agar diffusion, Isoelectrofocusing showed that the anti-thiomannose antibody preparation consisted of at least six isomeric proteins, all of which exhibited antibody activity against the glycoconjugate of thiomannose and BSA.

Animals↗

PubMed1988

Expression of glutathione peroxidase I gene in selenium-deficient rats.

We have characterized a cDNA pGPX1211 encoding rat glutathione peroxidase I. The selenocysteine in the protein corresponded to a TGA codon in the coding region of the cDNA, similar to earlier findings in mouse and human genes, and a gene encoding the formate dehydrogenase from E. coli, another selenoenzyme. The rat GSH peroxidase I has a calculated subunit molecular weight of 22,155 daltons and shares 95% and 86% sequence homology with the mouse and human subunits, respectively. The 3'-noncoding sequence (greater than 930 bp) in pGPX1211 is much longer than that of the human sequences. We found that glutathione peroxidase I mRNA, but not the polypeptide, was expressed under nutritional stress of selenium deficiency where no glutathione peroxidase I activity can be detected. The failure of detecting any apoprotein for the glutathione peroxidase I under selenium deficiency and results published from other laboratories supports the proposal that selenium may be incorporated into the glutathione peroxidase I co-translationally.

Amino Acid Sequence↗

PubMed1988

Characterization and heterospecific expression of cDNA clones of genes in the maize GSH S-transferase multigene family.

We have isolated from a constructed lambda gt11 expression library two classes of cDNA clones encoding the entire sequence of the maize GSH S-transferases GST I and GST III. Expression of a full-length GST I cDNA in E. coli resulted in the synthesis of enzymatically active maize GST I that is immunologically indistinguishable from the native GST I. Another GST I cDNA with a truncated N-terminal sequence is also active in heterospecific expression. Our GST III cDNA sequence differs from the version reported by Moore et al. [Moore, R. E., Davies, M. S., O'Connell, K. M., Harding, E. I., Wiegand, R. C., and Tiemeier, D. C. (1986) Nucleic Acids Res. 14:7227-7235] in eight reading frame shifts which result in partial amino acid sequence conservation with the rat GSH S-transferase sequences. The GST I and GST III sequences share approximately 45% amino acid sequence homology. Both the GST I and the GST III mRNAs contain different repeating motifs in front of the initiation codon ATG. Multiple poly(A) addition sites have been identified for these two classes of maize GSH S-transferase messages. Genomic Southern blotting results suggest that both GST I and GST III are present in single or low copies in the maize (GT112 RfRf) genome.

Amino Acid Sequence↗

PubMed1986

Immunological and sequence interrelationships between multiple human liver and rat glutathione S-transferases.

The 13 forms of human liver glutathione S-transferases (GST) (Vander Jagt, D. L., Hunsaker, L. A., Garcia, K. B., and Royer, R. E. (1985) J. Biol. Chem. 260, 11603-11610) are composed of subunits in two electrophoretic mobility groups: Mr = 26,000 (Ha) and Mr = 27,500 (Hb). Preparations purified from the S-hexyl GSH-linked Sepharose 4B affinity column revealed three additional peptides at Mr = 30,800, Mr = 31,200, and Mr = 32,200. Immunoprecipitation of human liver poly(A) RNAs in vitro translation products revealed three classes of GST subunits and related peptides at Mr = 26,000, Mr = 27,500, and Mr = 31,000. The Mr = 26,000 species (Ha) can be precipitated with antisera against a variety of rat liver GSTs containing Ya, Yb, and Yc subunits, whereas the Mr = 27,500 species (Hb) can be immunoprecipitated most efficiently by antiserum against the anionic isozymes as well as a second Yb-containing isozyme (peak V) from the rat liver. The Mr = 31,000 band can be immunoprecipitated by antisera preparations against sheep liver, rat liver, and rat testis isozymes. Human liver GSTs do not have any subunits of the rat liver Yc mobility. Antiserum against the human liver GSTs did not cross-react with the Yc subunits of rat livers or brains in immunoblotting experiments. The human liver GST cDNA clone, pGTH1, selected human liver poly(A) RNAs for the Ha subunit(s) in the hybrid-selected in vitro translation experiments. Southern blot hybridization results revealed cross-hybridization of pGTH1 with the Ya, Yb, and Yc subunit cDNA clones of rat liver GSTs. This sequence homology was substantiated further in that immobilized pGTH1 DNA selected rat liver poly(A) RNAs for the Ya, Yb, and Yc subunits with different efficiency as assayed by in vitro translation and immunoprecipitation. Therefore, we have demonstrated convincingly that sequence homology as well as immunological cross-reactivity exist between GST subunits from several rat tissues and the human liver. Also, the multiple forms of human liver GSTs are most likely encoded by a minimum of three different classes of mRNAs. These results suggest a genetic basis for the subunit heterogeneity of human liver GSTs.

Animals↗

PubMed1986

Expression of glutathione S-transferases in rat brains.

The tissue-specific expression of glutathione S-transferases (GSTs) in rat brains has been studied by protein purification, in vitro translation of brain poly(A) RNAs, and RNA blot hybridization with cDNA clones of the Ya, Yb, and Yc subunit of rat liver GSTs. Four classes of GST subunits are expressed in rat brains at Mr 28,000 (Yc), Mr 27,000 (Yb), Mr 26,300, and Mr 25,000. The Mr 26,3000 species, or Y beta, has an electrophoretic mobility between that of Ya and Yb, similar to the liver Yn subunit(s) reported by Hayes (Hayes, J. D. (1984) Biochem. J. 224, 839-852). RNA blot hybridization of brain poly(A) RNAs with a liver Yb cDNA probe revealed two RNA species of approximately 1300 and approximately 1100 nucleotides. The band at approximately 1300 nucleotides was absent in liver poly(A) RNAs. The Mr 25,000 species, or Y delta, can be immunoprecipitated by antisera against rat heart and rat testis GSTs, but not by antiserum against rat liver GSTs. Therefore, the Y delta subunit may be related to the "Mr 22,000" subunit reported by Tu et al. (Tu, C.-P.D., Weiss, M.J., Li, N., and Reddy, C. C. (1983) J. Biol. Chem. 258, 4659-4662). The abundant liver GST subunits, Ya, are not expressed in rat brains as demonstrated by electrophoresis of purified brain GSTs and a lack of isomerase activity toward the Ya-specific substrate, delta 5-androstene-3,17-dione. This is apparently because of the absence of Ya mRNA expression prior to RNA processing. The data on the preferential expression of Yc subunits in rat brains, together with the differential phenobarbital inducibility of the Ya subunit(s) in rat liver reported by Pickett et al. (Pickett, C. B., Donohue, A. M., Lu, A. Y. H., and Hales, B. F. (1982) Arch. Biochem. Biophys. 215, 539-543), suggest that the Ya and Yc genes for rat GSTs are two functionally distinct gene families even though they share 68% DNA sequence homology. The expression of multiple GSTs in rat brains suggests that GSTs may be involved in physiological processes other than xenobiotics metabolism.

Animals↗

PubMed1986

Suppression of glutathione S-transferases in rat seminal vesicles or pituitary glands.

We have studied the tissue-specific expression of GSH S-transferases in rat seminal vesicles and pituitary glands by in vitro translation and immunoprecipitation. The major GSH S-transferase subunit expressed in rat seminal vesicles belongs to the Yb mobility class whose expression diminishes when the rats are treated with pentobarbital. The pattern of GSH S-transferase expression in the pituitary gland is very similar to that of the rat brain with Yb size subunit(s) predominant. The Y beta size subunit is also expressed together with the Yc and Y delta subunits. The expression of GSH S-transferases was drastically reduced in pituitary gland poly(A) RNAs from diethylstilbestrol-treated, ovariectomized female rats. Xenobiotics such as phenobarbital, 3-methylcholanthrene, and trans-stilbene oxide induce rat liver GSH S-transferase activities, especially the Ya- and Yb-subunit containing isozymes. Induction of GSH S-transferases by a combination of the three xenobiotics is neither additive nor synergistic, however. Our results clearly demonstrate that GSH S-transferase expression in seminal vesicles and pituitary glands can be suppressed by phenobarbital and diethylstilbestrol, respectively. Our findings suggest that different GSH S-transferase isozymes respond differently to various xenobiotics. Both induction and suppression occur in rats treated with xenobiotics. This notion helps to explain the lack of additive or synergistic induction in rats treated with more than one xenobiotic.

Animals↗

PubMed1984

The Yc and Ya subunits of rat liver glutathione S-transferases are the products of separate genes.

Rat liver glutathione S-transferases consist of binary combinations of three major classes of subunits designated as Ya (Mr = 25,600), Yb (Mr = 27,000) and Yc (Mr = 28,000). We have determined the nucleotide sequences of a cDNA insert in pGTR262 containing partial sequence of a Yc subunit. Sequence comparison with a Ya subunit cDNA clone pGTR261 revealed 70% nucleotide sequence homology and 65% amino acid sequence homology in the overlapping coding regions. Approximately 65% of the amino acid substitutions between these two subunits occur in clusters of two to eight residues. The 3' noncoding sequences of these two subunit cDNA clones are highly divergent in length and in sequences. The 3' noncoding region of pGTR262 cDNA contains open reading frames of 23, 39, and 13 amino acids which are in phase with the deduced Yc subunit sequences but interrupted by termination codons. By RNA blot hybridization analysis, we found that this Yc subunit sequence expression is tissue specific. It is expressed at a reduced level in kidney and testis as compared with liver and hardly at all in heart, lung, seminal vesicles, and spleen. We suggest that the mechanism for the tissue-specific expression of the Yc subunit of rat liver glutathione S-transferases may occur at or prior to the level of RNA processing. From the divergent DNA sequences between the Ya and Yc subunits reported in this communication and their differential induction upon acute phenobarbital administration reported by Pickett et al. (Pickett, C.B., Donohue, A. M., Lu, A. Y. H., and Hales, B. F. (1982) Arch. Biochem. Biophys. 215, 539-543) we propose that the Ya and Yc subunits of rat liver glutathione S-transferases are encoded by separate gene families or transcriptional units.

Amino Acid Sequence↗