Glutaminase inhibition impairs CD8 T cell activation in STK11-/Lkb1-deficient lung cancer

The tumor microenvironment (TME) contains a rich source of nutrients that sustains cell growth and facilitate tumor development. Glucose and glutamine in the TME are essential for the development and activation of effector T cells that exert antitumor function. Immunotherapy unleashes T cell antitumor function, and although many solid tumors respond well, a significant proportion of patients do not benefit. In patients with KRAS-mutant lung adenocarcinoma, KEAP1 and STK11/Lkb1 co-mutations are associated with impaired response to immunotherapy. To investigate the metabolic and immune microenvironment of KRAS-mutant lung adenocarcinoma, we generated murine models that reflect the KEAP1 and STK11/Lkb1 mutational landscape in these patients. Here, we show increased glutamate abundance in the Lkb1-deficient TME associated with CD8 T cell activation in response to anti-PD1. Combination treatment with the glutaminase inhibitor CB-839 inhibited clonal expansion and activation of CD8 T cells. Thus, glutaminase inhibition negatively impacts CD8 T cells activated by anti-PD1 immunotherapy.

Expression of recombinant human L-glutaminase in Escherichia coli: polyclonal antibodies production and immunological analysis of mouse tissues

The first complete sequence of human L-glutaminase was deduced from breast cancer glutaminase cDNA cloned in our laboratory. This cDNA clone has now been engineered to synthesize both precursor and mature forms of the protein in Escherichia coli. Among several different plasmid constructions, the expression system based on phage T7 promoter (vector pET-3c) was found to be the most efficient for glutaminase overproduction. Upon induction, precursor glutaminase accounts for about 25% of total E. coli protein, whereas a lower amount (12%) was achieved for the putative mature protein. The optimal length of the translational spacer on the ribosome binding site was shown to be eight nucleotides. However, using this length of spacer, we were unable to obtain expression in the pQE vector, tagged with a 6x His sequence at the NH(2)-terminus, stressing the importance of the 5'-coding sequence in the expression efficiency. Although the precursor and mature recombinant forms of glutaminase were devoid of catalytic activity, the purified protein allowed us to obtain highly specific polyclonal antibodies, as shown by immunoblot analysis of mouse tissues. Furthermore, the antibodies were able to immunoprecipitate the in vitro translated enzyme using a reticulocyte lysate system; these antibodies might be a valuable tool for studies on L-glutaminase expression in mammalian tissues.

Neurotransmission in the vestibular endorgans--glutamatergic transmission in the afferent synapses of hair cells

In the sensory pathways the first synapse is that between hair cells and primary afferent neurons and its most likely neurotransmitter candidate has long been thought to be glutamate. A number of pharmacological and electrophysiological studies have lent credence to this theory (reviewed by Bledsoe et al. 1988, Bobbin 1979, Ehrenberger and Felix 1991, Puel et al. 1991; Puel 1995) as has recent neurochemical and immunocytochemical work (reviewed by Ottersen et al. 1998; Usami et al. 2000). These recent studies reveal that the afferent hair cell synapse resembles the central glutamate synapses in many ways. Of the proteins confirmed to be involved in signal transduction and transmitter metabolism at most central synapses, many are also seen in the afferent hair cell synapse, and have an analogous compartmentation. On the other hand, there are also important differences, especially those related to the molecular mechanisms that underlie transmitter release.

Ehrlich ascites tumor cells expressing anti-sense glutaminase mRNA lose their capacity to evade the mouse immune system

Glutaminase (EC 3.5.1.2) is a key enzyme in rapidly proliferating cells. Using anti-sense technology, an Ehrlich ascites tumor cell line (0.28AS-2) with reduced glutaminase activity has been obtained. We investigated the in vivo growth characteristics of the 0.28AS-2 cells. When injected i.p. into normal Swiss albino mice, the 0.28AS-2 cells were unable to grow. On the contrary, when injected into nude mice, they developed into solid tumors. Mice inoculated with 0.28AS-2 cells kept immunologic memory and rejected a second inoculation with parental Ehrlich ascites tumor cells. Expression of both polymorphic epithelial mucin-1 (MUC-1) and the enzyme N-acetyl-alpha-D-galactosaminidase, proteins implicated in host immune system escape, were markedly diminished in 0.28AS-2 cells. Study of the immune system response in mice inoculated with 0.28AS-2 cells revealed an increase in splenic CD18 cells and the presence of a large number of activated F4/80+ macrophages in the ascites cavity. These features, not observed in mice inoculated with parental Ehrlich ascites tumor cells, indicate that a distinctive, strong immune response occurred in animals inoculated with 0.28AS-2 cells. Our results suggest that inhibition of glutaminase expression using anti-sense technology induces phenotypic changes in Ehrlich ascites tumor cells that allow the development of an effective anti-tumor immune response, which makes the cells unable to develop in vivo tumors.

[Antibodies against tissue transglutaminase as a serological marker in dermatitis herpetiformis During]

Dermatitis herpetiformis is associated with celiac disease. IgA antibodies to endomysium are considered as sensitive and specific markers for celiac disease. Recently, tissue transglutaminase was identified as the antigen of anti-endomysium antibodies. Moreover, serum levels of IgA antibodies to tissue transglutaminase were found to correlate with titers of IgA antibodies to endomysium in patients with both celiac disease and dermatitis herpetiformis. These findings confirm the close pathogenic relation between the two diseases. The determination of serum levels of antibodies to tissue transglutaminase may be a tool that can be routinely used for the diagnosis of dermatitis herpetiformis in the future.

Characterization of glutaminase in the developing rat small intestine

As a primary substrate in the small intestine, glutamine is a very important source of energy. Glutaminase (GA) is the enzyme involved in the deamination of glutamine to glutamate, which is utilized for energy production via the TCA cycle. Although the enzymatic activity of GA in the small intestine is known to undergo maturational changes, the tissue localization of the protein and its mRNA, the intracellular processing of this enzyme and levels of its mRNA in the small intestine at different maturational stages have not yet been described. In this study, using immuno-histochemical staining, we confirm previous studies using other techniques that suggested GA is localized in the epithelial layer of the rat small intestine. Some GA is also found in cells of the lamina propria and crypt epithelium. Using in situ hybridization studies, we have corroborated the presence of the protein in the epithelial cells of the villi by localizing the mRNA of this protein to the same layer and its precursor layer in the crypt region. An ontogenic analysis of GA mRNA and protein from rat small intestines, using RNA dot blots, gel blots and protein immunoblotting revealed differences in immunoreactive GA protein and mRNA during maturation. Immunoreactive GA and steady-state levels of GA mRNA increased around the 3rd wk of life, coincident with weaning and the endogenous glucocorticoid surge. Whether these findings have nutritional or pathophysiological implications remains speculative.

Tumor glutaminase purification

Two alternative purification schemes to obtain the glutaminase from Ehrlich tumor cells in a highly purified form have been developed. One experimental approach is based on conventional and high-performance liquid chromatography fractionation techniques, yielding a 37-fold higher purification than has been previously reported. The method comprises: isolation of mitochondria, solubilization with Triton X-100, ion-exchange and hydroxyapatite chromatography, ammonium sulfate precipitation, and hydrophobic interaction chromatography. A second purification schedule has been optimized employing native polyacrylamide gel electrophoresis, in situ activity staining, and electroelution of the protein band. This approach resulted in a simple and rapid isolation of a 10-fold higher purified glutaminase than before, minimizing also the potential for proteolytic inactivation of the enzyme. The apparent molecular weight of the protein in native form was determined by gel filtration and sucrose density gradient ultracentrifugation. Polyclonal antibodies raised against Ehrlich glutaminase were immunopurified against the pig kidney enzyme. Immunoblot analyses employing these antibodies as well as anti-rat kidney glutaminase antibodies revealed the same pattern of bands seen with the purified enzyme.

The vitamin D3 hydroxylase-associated protein is a propionamide-metabolizing amidase enzyme

Previously we isolated a novel protein that coimmunoprecipitates with the 1,25-dihydroxyvitamin D3-24R-hydroxylase and 25-hydroxyvitamin D3-1 alpha-hydroxylase. This kidney-specific protein found in the inner membrane of mitochondria is named the vitamin D3 hydroxylase-associated protein (VDHAP). To determine a putative function for this protein, an extensive computer search of the deduced amino acid sequence of VDHAP was performed. A BLAST homology search identified amino acid residues 133 through 321 in acetamidase from Aspergillus nidulans that exhibit 38% amino acid identify and 65% amino acid similarity to VDHAP. A protein consensus sequence dictionary, MOTIFS, identified an amidase consensus sequence in VDHAP. This sequence, G-G-S-S-G-G-E-G-A-L-I-A-G-G-G-S-L-L-G-I-G-S-D-V-A-G-S-I-R-L-P-S, in VDHAP is located between amino acids 223 and 254. Propionamide, acetamide, and acrylamide were identified as substrates for an amidase activity in soluble chicken kidney mitochondria. Propionamide is the best substrate with a Vmax of 16.7 nmol NH4+/min/mg protein and an apparent Km of 7.9 mM in soluble chicken kidney mitochondria. A VDHAP monoclonal antibody, IVC2G8, immunoprecipitates 78% of the total propionamidase activity in soluble chicken kidney mitochondria. These results suggest that VDHAP is a propionamidase enzyme in soluble chicken kidney mitochondria and a member of the amidase signature gene family.

Glutaminase immunoreactive neurons in the rat dorsal root ganglion contain calcitonin gene-related peptide (CGRP)

The co-localization of glutaminase and calcitonin gene-related peptide (CGRP) was examined with immunohistochemistry in the rat dorsal root ganglion (DRG). The majority of the DRG neurons were immunoreactive for glutaminase and all DRG neurons that contained CGRP also contained glutaminase. These results indicate that some DRG neurons release glutamate and CGRP from the same axon terminals in the spinal cord. Co-release of glutamate and CGRP from primary afferents may have multiple effects including fast and slow neurotransmission of sensory information in the spinal cord.

Paucity of glutaminase-immunoreactive nonpyramidal neurons in the rat cerebral cortex

Glutaminase has been considered to be a synthesizing enzyme of transmitter glutamate in pyramidal neurons of the cerebral cortex. In the present study, an attempt was made to examine with a double immunofluorescence method whether or not nonpyramidal neurons of the cerebral cortex are immunoreactive for glutaminase. Glutaminase was stained with mouse anti-glutaminase IgM and FITC-labeled anti-[mouse IgM] antibody. In the same section, parvalbumin (PA), calbindin (CB), choline acetyltransferase (CAT), vasoactive intestinal polypeptide (VIP), corticotropin releasing factor (CRF), cholecystokinin (CCK), somatostatin (SS), or neuropeptide Y (NPY) was visualized as a marker for nonpyramidal neurons with an antibody to each substance, biotinylated secondary antibody and Texas Red-labeled avidin. Virtually no glutaminase immunoreactivity was seen in PA-, CB-, CAT-, VIP-, CRF-, CCK-, SS-, or NPY-immunoreactive neuronal perikarya in the neocortex and mesocortex (cingulate and retrosplenial cortices), although it was detected in a few PA-, CB-, VIP-, CCK-, SS-, or NPY-immunoreactive nonpyramidal neurons in the piriform, entorhinal, and hippocampal cortices. PA- and CB-positive neurons have been reported to constitute the major population of GABAergic neurons in the cerebral cortex. Thus, the present results, together with the previous reports, suggest that most GABAergic, cholinergic and peptidergic nonpyramidal neurons in the neo- and mesocortex do not contain glutaminase.

Mosaic distribution of phosphate-activated glutaminase-like immunoreactivity in the rat striatum

The dorsal and ventral striatum of mammals has been known to be organized in a mosaic manner, referred to as "patches" and "matrix" of the caudatoputamen. The present study was primarily attempted in order to reveal the relationship of glutamatergic neuronal components to the mosaic organization in the rat striatum by using a monoclonal antibody to phosphate-activated glutaminase, a major synthetic enzyme of transmitter glutamate. Antibodies against glutamate decarboxylase and choline acetyltransferase were also used as the markers for GABAergic and cholinergic neuronal components, respectively. Glutaminase immunoreactivity was seen in a number of large- and a few medium-sized neurons in the caudatoputamen, nucleus accumbens and olfactory tubercle. The large neurons with glutaminase immunoreactivity were observed in the neuropil of the caudatoputamen and nucleus accumbens; glutaminase immunoreactivity was particularly marked in the neuropil of island-like patchy areas although it was seen throughout the neuropil of the nuclei. In the caudatoputamen, island-like areas with marked glutaminase immunoreactivity exhibited less marked choline acetyltransferase immunoreactivity than the surrounding background region, and were thus considered to correspond to the patches. The mosaic distribution of glutamate decarboxylase immunoreactivity in the caudatoputamen seemed identical with that of glutaminase immunoreactivity. However, in the nucleus accumbens, the mosaic pattern of neuropil labeling for glutaminase was neither consistent with that for glutamate decarboxylase nor that for choline acetyltransferase, suggesting the presence of non-GABAergic glutaminase-containing nerve terminals in the nucleus. In an attempt to clarify the origin of neuropil labeling for glutaminase in the striatum, lesions were made in the regions sending projection fibers to the caudatoputamen and nucleus accumbens. After placing lesions in the cerebral cortex, glutaminase immunoreactivity was decreased in neuropil of the caudatoputamen, but the mosaic pattern remained. Lesions which were placed in the intralaminar thalamic nuclei, amygdaloid body, globus pallidus or substantia nigra produced no substantial change in glutaminase immunoreactivity in the caudatoputamen and nucleus accumbens. After injection of kainic acid into the caudatoputamen or nucleus accumbens, glutaminase immunoreactivity in the neuropil of the affected regions was decreased to lose the mosaic pattern, indicating that neuronal components with glutaminase immunoreactivity in the neuropil of the patches were mainly of intrinsic origin. In summary, possible axon terminals containing glutaminase were observed with mosaic patterns in the caudatoputamen and nucleus accumbens, in which large cholinergic and medium-sized non-cholinergic neurons were immunoreactive for glutaminase. In the caudatoputamen, glutaminase immunoreactivity in neuropil was more marked in the patches than in the matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of glutaminase-like immunoreactivity in rat brain by an irreversible inhibitor of the enzyme

Changes of glutaminase immunoreactivity in rat brain were examined after intracranial injection of 6-diazo-5-oxo-L-norleucine (DON), an irreversible inhibitor of glutaminase. When 1 M DON was injected into the lateral ventricle, a half-lethal dose was 7.5-10 mumol. After intraventricular injection of 2-7.5 mumol DON, glutaminase immunoreactivity was dose dependently enhanced with the maximum enhancement 3-5 days after the injection. The enhanced glutaminase immunoreactivity was recognized by enlarged granular immunodeposits in both perikarya and neuropil in many regions, such as the hippocampus, thalamus, hypothalamus, periaqueductal gray, and some brain stem, cerebellar, and spinal cord regions. Intrathalamic injection of 0.2 mumol DON enhanced glutaminase immunoreactivity in many neuronal perikarya in the thalamus and in some perikarya in layer VI of the cerebral cortex. Intrastriatal injection of the same dose of DON enhanced glutaminase immunoreactivity in neuropil of the caudoputamen and in many neuronal perikarya of the intralaminar thalamic nuclei. These results suggested that DON induced a new massive synthesis of glutaminase in the affected neurons.

Monoclonal antibodies against bacterial glucosamine 6-phosphate synthase: production and use for structural studies

Fifteen mouse x rat hybridoma cell lines producing rat monoclonal antibodies (MAbs) directed to Escherichia coli Glucosamine 6-P Synthase (GlmS) were established and characterized. Most of them (13/15) are IgG2a while 2 were typed as IgG1. Their Kaff ranged from 1.5 x 10(6) to 9.6 x 10(8) M-1 as determined by Beatty et al. (1). The epitopes recognized by these MAbs were assigned to one of the two catalytical domains of the enzyme (CT1 and CT2) as demonstrated both by ELISA and Western-blotting using purified GlmS proteolytic fragments. The binding of the MAbs on either the native or denatured forms of GlmS, CT1 and CT2 was further analyzed by competitive immunoassay and most of the MAbs were found to bind preferentially to the denatured proteins. The study of the antigenic topography of GlmS by competitive radioimmunoassay demonstrated the existence of at least 10 independent epitopes on GlmS, divided into three groups. The first one (3/15) includes MAbs whose binding was not inhibited by any of the other MAbs. The second group (9/15) is comprised of MAbs that exhibit reciprocal binding inhibitory activity while the third group includes MAbs (3/15) presenting asymmetric inhibitory activity. Finally, since most of the isolated antibodies (10/15) bind to the 27 kDa amino-terminal glutamine binding domain (CT2), the capacity of these MAb to interfere with the associated glutaminase activity was analyzed.

Glutamate in spinally projecting neurons of the rostral ventral medulla

Phosphate activated glutaminase (PAG), an enzyme of glutamate synthesis, was localized by immunohistochemistry in all PNMT-immunoreactive and all serotonin-immunoreactive neurons in the rostral ventral medulla of the rat. Between 71 and 83% of bulbospinal neurons localised in the rostral ventral medulla projecting to the intermediolateral cell column in the upper thoracic spinal cord contained PAG immunoreactivity. Of these bulbospinal PAG-immunoreactive neurons 17-27% contained PNMT immunoreactivity and 9-16% contained serotonin immunoreactivity. Other bulbospinal PAG-immunoreactive neurons (60-70%) contained neither PNMT- nor serotonin immunoreactivity. The results provide anatomical evidence suggestive of a glutamatergic input to the sympathetic preganglionic neurons of the spinal cord arising from different populations of neurons located in the rostral ventral medulla.

Molecular cloning of a cDNA for rat hepatic glutaminase. Sequence similarity to kidney-type glutaminase

Mammalian liver possesses a unique isozyme of phosphate-activated glutaminase which plays an important role in the regulation of glutamine catabolism. Antibodies to hepatic glutaminase were used to screen a lambda gt11 rat liver cDNA library. One cDNA to hepatic glutaminase was identified. Changes in the relative abundance of hepatic glutaminase mRNA were determined by hybridization to this cDNA. The mRNA is found only in liver; it is not present prior to birth but its abundance increases dramatically at birth. The abundance of the mRNA is increased approximately 4-fold in diabetes. The sequence of the cDNA was compared to that recently published for kidney (brain)-type glutaminase (Banner, C., Hwang, J.-J., Shapiro, R.A., Wenthold, R.J., Nakatani, Y., Lampel, K.A., Thomas, J.W., Huie, D., and Curthoys, N.P. (1988) Mol. Brain Res. 3, 247-254). When the predicted amino acid sequences were compared a region of 123 amino acids with greater than 80% identity was found. The presence of scattered amino acid substitutions within stretches of identical amino acids suggests that the glutaminase isozymes are encoded by separate genes. This is the first demonstration of any similarity between the two glutaminases at the molecular level.

Metabolism of glutamate and ammonia in astrocyte: an immunocytochemical study

Alpha-ketoglutarate (alpha-KG) reductive amination activity in rat brain was found to be mostly absorbed with an antibody against liver glutamate dehydrogenase. With this and anti-glutamine synthetase antibodies, alpha-KG reductive amination activity was immunocytochemically shown to coexist with glutamine synthetase activity in astrocytes. The results suggest that astrocytes de novo synthesize glutamate from alpha-KG and ammonia, and metabolize it to glutamine.

Correlation between immunochemical characteristics and immunohistochemical applicability of nine lines of monoclonal antibodies against rat brain glutaminase

Nine lines of monoclonal IgM antibodies to rat brain glutaminase were produced from a mouse. The antibodies were named MAb-19, -21, -45, -48, -51, -55, -59, -97, and -120. Immunotitration tests revealed that six of the nine antibodies (MAb-19, -21, -45, -48, -97, and -120) absorbed dose-dependently more than 75% of glutaminase activity in rat brain. By immunoelectroblotting after gel electrophoresis of the homogenate, all antibodies showed a positive band at the same position as that of the purified enzyme. However, MAb-55, -59, and -97 crossreacted with other proteins. Despite the difference in their specificities, all of the antibodies except MAb-51 competed with one another for determinants on the enzyme. The competition test further indicated that the affinities of the antibodies were in the order MAb-120 greater than -21 greater than -48 greater than -19 not equal to -45 greater than or equal to -97 greater than or equal to -55 greater than or equal to 59. When applied to immunohistochemical staining of cerebral cortex of rat brain, the five specific antibodies (MAb-19, -21, -45, -48, and -120) produced essentially the same pattern of neuronal labeling; they labeled specifically pyramidal neurons, which are reportedly glutamatergic. The most intense labeling was obtained with MAb-120.

Immunohistochemical study of glutaminase-containing neurons in the cerebral cortex and thalamus of the rat

In an attempt to identify glutamatergic neurons, the cerebral cortex and thalamus of the rat were examined immunohistochemically by using a monoclonal antibody against phosphate-activated glutaminase (PAG), a major synthetic enzyme of transmitter glutamate in the central nervous system. In both the neocortex and mesocortex, pyramidal cells in layers V and VI showed intense PAG-like immunoreactivity (PAG-LI), whereas neuronal cell bodies in layers I-IV showed weak PAG-LI. At the deep border of layer VI, neurons with horizontally elongated cell bodies showed PAG-LI. In the pyriform and entorhinal cortices, neurons with intense to moderate PAG-LI were seen in layer II as well as in the deeper layers. In the hippocampal formation, pyramidal cells in CA1, CA2, and CA3 and polymorphic cells in CA4 showed PAG-LI; PAG-LI was most intense in pyramidal cells of CA3. Fine granules with weak PAG-LI were also seen on and/or within the cell bodies of granule cells in the dentate gyrus. In the thalamus, neurons with PAG-LI were distributed in all nuclei, although regional differences were observed in the distribution pattern of neurons with PAG-LI and in the intensity of PAG-LI in individual neurons. The largest neurons in each thalamic nucleus showed intense PAG-LI; these were considered to be projection neurons. In addition to perikaryal labeling, many fine, PAG-like immunoreactive granules were distributed in the neuropil of both the cerebral cortex and thalamic nuclei. Some of these fine granules with PAG-LI in the neuropil were assumed to represent fiber terminals with PAG-LI, because the distribution pattern of the deposits in the primary somatosensory and primary visual cortices resembled that of thalamocortical fiber terminals. Glutamate is rather ubiquitous in the mammalian central nervous system, and it is still debatable whether the monoclonal antibody to PAG from brain mitochondria can distinguish transmitter-related glutaminase from the other metabolism-related ones. In the present study, however, large neurons in the thalamic nuclei, as well as pyramidal neurons in the cerebral cortex, showed PAG-LI most intensely, supporting the assumption that projection neurons of the cerebral cortex and thalamus are primarily glutamatergic.

Effects of the blocking agents bovine serum albumin and Tween 20 in different buffers on immunoblotting of brain proteins and marker proteins

The effects of the blocking agents bovine serum albumin and Tween 20 in buffers at pH values 7.2 and 10.2 were compared in immunoblotting with 2 different antisera. The antisera were raised against a purified brain-specific protein fraction from human brain, soluble in perchloric acid, and phosphate-activated glutaminase from pig brain, respectively. The antigens were a crude perchloric acid-soluble brain extract, a crude brain phosphate-activated glutaminase fraction, and proteins commonly used as molecular weight markers. The binding patterns of the 2 antisera to the respective brain antigen preparations changed, depending on the blocking agent and the pH of the blocking buffer. Also, antibody binding to the molecular weight marker proteins was observed with some of the blocking buffers. Immunoblotting with Tris-saline, pH 10.2, containing 3% bovine serum albumin as blocking agent and diluting buffer for the antisera, showed negligible antibody binding to the marker proteins and most specific binding to the brain antigens.

Monoclonal antibodies specific for bovine pancreatic asparagine synthetase. Production and use in structural studies

Thirteen stable hybridoma cell lines producing monoclonal antibodies specific for asparagine synthetase were established and one monoclonal antibody was chosen to produce an immunoaffinity resin for the purification of asparagine synthetase. Bovine pancreatic asparagine synthetase was purified to a specific activity of 395 nmol of Asn produced/min/mg. Electrophoresis of the affinity-purified enzyme in sodium dodecyl sulfate polyacrylamide gels resulted in a single Mr = 54,000 polypeptide. Prior cross-linking with dimethyl suberimidate resulted in a band at Mr = 52,500 (monomer) and two additional bands at Mr = 97,000 and 98,000 (dimers), suggesting the possibility of a heterogeneous enzyme population with slight differences in subunit composition. The ratio of Gln-dependent and NH3-dependent asparagine synthetase activities was constant for immunoaffinity-purified enzyme, but the ratios of glutaminase activity to synthetase activities varied, suggesting separate aspartate and glutamine binding sites. The monoclonal antibodies were tested as inhibitors of the Gln-dependent and NH3-dependent asparagine synthetase activities as well as for inhibition of the glutaminase activity of the enzyme. Two antibodies inhibited Gln- and NH3-dependent synthesis of asparagine, but did not affect the glutaminase activity of immunoaffinity-purified asparagine synthetase. A third monoclonal antibody inhibited Gln-dependent synthesis of asparagine and glutaminase activity, but activated NH3-dependent asparagine synthetase activity. These data are discussed in terms of multiple substrate binding domains within the asparagine synthetase molecule.

The effect of metabolic acidosis on the synthesis and turnover of rat renal phosphate-dependent glutaminase

Regulation of the mitochondrial phosphate-dependent glutaminase activity is an essential component in the control of renal ammoniagenesis. Alterations in acid-base balance significantly affect the amount of the glutaminase that is present in rat kidney, but not in brain or small intestine. The relative rates of glutaminase synthesis were determined by comparing the amount of [35S]methionine incorporated into specific immunoprecipitates with that incorporated into total protein. In a normal animal, the rate of glutaminase synthesis constitutes 0.04% of the total protein synthesis. After 7 days of metabolic acidosis, the renal glutaminase activity is increased to a value that is 5-fold greater than normal. During onset of acidosis, the relative rate of synthesis increases more rapidly than the appearance of increased glutaminase activity. The increased rate of synthesis reaches a plateau within 5 days at a value that is 5.3-fold greater than normal. Recovery from chronic acidosis causes a rapid decrease in the relative rate of glutaminase synthesis, but a gradual decrease in glutaminase activity. The former returns to normal within 2 days, whereas the latter requires 11 days. The apparent half-time for glutaminase degradation was found to be 5.1 days and 4.7 days for normal and acidotic rats respectively. These results indicate that the increase in renal glutaminase activity associated with metabolic acidosis is due primarily to an increase in its rate of synthesis. From the decrease in activity that occurs upon recovery from acidosis, the true half-life for the glutaminase was estimated to be 3 days.

Localization of glutaminase-like and aspartate aminotransferase-like immunoreactivity in neurons of cerebral neocortex

The distribution of glutaminase (GLNase)- and aspartate aminotransferase (AATase)-immunoreactive cells was examined in the cerebral neocortex of rat and guinea pig and in the somatic sensorimotor and primary visual cortex of the Macaca fascicularis monkey. These enzymes are involved in the metabolism of glutamate and aspartate, two amino acids thought to be excitatory amino acid transmitters for cortical neurons. In each of the species examined a large percentage of layer V and VI pyramidal neurons have pronounced glutaminase-like immunoreactivity (GLNase IR). In contrast, neurons in layers I, II, and IV show little GLNase IR. Layer III in the rat and guinea pig contains only a few, densely labeled GLNase-like-immunoreactive (GLNase-Ir) pyramidal neurons, whereas in the monkey the number of GLNase-Ir cells in layer III varies between cytoarchitectonic fields. Area 3b of the primary somatic sensory cortex and area 17 (primary visual cortex) contain few GLNase-Ir cells in layer III. However, layer III contains moderate numbers of GLNase IR in cells in areas 3a, 1, 2, 5, and in the primary motor cortex. Within the motor cortex the largest pyramidal ("Betz") cells are not labeled. In marked contrast to the results with antibody to GLNase, antibody to AATase labels cells that appear nonpyramidal in form, and these cells are in all cortical layers in each of the species examined. This distribution is roughly similar throughout all areas of rodent neocortex, but in monkey visual cortex AATase-immunoreactive neurons are more numerous in layers II-III, IVc, and VI. When combined with the findings of other studies, our results suggest that GLNase IR marks pyramidal neurons that use an excitatory amino acid transmitter. Antibody to AATase appears to mark intrinsic cortical neurons. The AATase immunoreactivity of these cells could indicate that they use an excitatory amino acid transmitter. However, their form and distribution in cortex suggest that this antibody labels GABAergic neurons.

Comparison of the phosphate-dependent glutaminase obtained from rat brain and kidney

A phosphate-dependent glutaminase was purified 1200-fold from rat brain. In the absence of a polyvalent anion, the glutaminase exists as an inactive protomer which has an estimated Mr of 126000. The addition of 100mM-phosphate causes maximal activation and a dimerization (Mr 249000) of the glutaminase. The phosphate activation is sigmoidal, with a K0.5 of 25mM and a Hill coefficient (h) of 1.5 Glutamate inhibition is competitive with respect to glutamine and is decreased by increasing the concentration of phosphate. Phosphate also decreases the Km for glutamine. The purified glutaminase contains a predominant peptide (Mr 65000) and a minor peptide (Mr 68000) that are present in an approximate ratio of 4:1 respectively. The glutaminase immunoprecipitated from freshly solubilized brain tissue or from synaptosomal and non-synaptosomal brain mitochondria contains the same distribution of the two peptides. In contrast, the glutaminase purified from rat kidney contains five to seven peptides that range in Mr value from 59000 to 48000, and immunoprecipitates derived from freshly solubilized renal tissue contain only the Mr-65000 peptide. Partial proteolysis and size fractionation of the three immunoprecipitated peptides indicate that they are structurally related. The series of peptides characteristic of the purified renal glutaminase is generated on storage of the solubilized extract of kidney tissue. The glutaminase contained in the solubilized brain extract is not degraded unless a renal extract is added. Thus the difference in the pattern of peptides associated with the two purified enzymes is due to an endogenous renal proteinase that is not present in brain.

[Comparison of the immunodepressive action of microbial deamidases from different sources]

The role of glutaminase activity of microbial deamidases in the immunodepressant action of these enzymes was studied. Escherichia coli asparaginase, asparagin and glutamin deamidases from Pseudomonas fluorescens and Mycobacterium album were found to have an inhibitory effect on the PHA-stimulated lymphocyte blast transformation. The inhibitory activity of deamidases with the asparaginase-glutaminase ratios 1 : 1.5 and 1 : 1.3 was one order of magnitude higher than that of Escherichia coli asparaginase with the ratio 1 : 0.02. It is assumed that glutaminase activity plays an essential role in the immunodepressant action of deamidases .