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Factors influencing the inactivation of phosphate-dependent glutaminase in the matrix fraction of rat liver mitochondria.

ABSTRACT: 1. The activity of phosphate-dependent glutaminase was measured in a matrix extract of essentially lysosome-free liver mitochondria. 2. ATP, GTP or a non-hydrolysable analogue of ATP stimulated the rapid inactivation of glutaminase, but not of other matrix enzymes. 3. Glutaminase was protected against inactivation if high concentrations of glutamine or low concentrations of NH3 were present. 4. Inactivation of glutaminase in the presence of ATP did not markedly affect the reaction of the enzyme with a specific polyclonal antiserum. 5. These results in a mitochondrial extract are similar to the characteristics of glutaminase inactivation in intact hepatocytes, suggesting a similar mechanism in each case. 6. The presence of a specific ATP-activated protease in the mitochondrial matrix is suggested to be responsible for glutaminase inactivation.

SUBMITTER: McGivan JD

PROVIDER: S-EPMC1149927 | biostudies-other | 1991 Feb

REPOSITORIES: biostudies-other

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Localization and some properties of phosphate-dependent glutaminase in disrupted liver mitochondria.

Project description:1. Glutaminase activity in frozen and thawed liver mitochondria was activated by NH4+, phosphate and HCO3-ions and also by ATP . 2. NH4+ and HCO3-ions decreased the requirement of the enzyme for phosphate. The activation by ATP was observed only in the presence of NH4+ or HCO3-ions. 3. In frozen-and-thawed mitochondria, the enzyme was loosely bound to the inner membrane, the Arrhenius plot showing a break at 23 degrees C. On sonication, glutaminase was detached from the membrane and the Arrhenius plot became linear. 4. The apparent Km for glutamine of the membrane-bound form was 6 mM, and that of the soluble form was 21 mM. 5. It is likely that the properties of glutaminase in the intact cell are dependent on the association of this enzyme with the mitochondrial membrane.

| S-EPMC1162368 | biostudies-other

Influence of phospholipids on the activity of phosphate-dependent glutaminase in extracts of rat liver mitochondria.

Project description:Liver glutaminase can be solubilized from frozen-and-thawed mitochondria by treatment with phospholipase A2. Solubilization by this technique markedly changes the kinetic properties of the enzyme. The properties of the membrane-bound form of the enzyme are partially restored by adding phosphatidylcholine or phosphatidylethanolamine to the phospholipase extract. It is concluded that the kinetic properties of liver glutaminase are a function of the interaction of this enzyme with membrane phospholipids.

| S-EPMC1152294 | biostudies-other

Increased activity of phosphate-dependent glutaminase in liver mitochondria as a result of glucagon treatment of rats.

Project description:1. Injection of rats with glucagon leads to an increased effective activity of glutaminase in subsequently isolated liver mitochondria. 2. This effect of glucagon is manifested as a decreased requirement of glutaminase for phosphate in the presence of HCO3-. The HCO3--concentration-dependence is unchanged. 3. The effect of glucagon is lost on disruption of the mitochondria. 4. In accordance with previous reports, incubation of mitochondria in hypo-osmotic media also increases the effective activity of glutaminase. Glucagon increases glutamine hydrolysis at intermediate osmolarities of the suspending medium, but does not affect glutaminase activity when it is already maximally activated by hypo-osmotic conditions. 5. From this and previous work, it seems that hypo-osmotic incubation conditions, EDTA and glucagon may all activate glutaminase by a common mechanism. It is postulated that this mechanism involves modification of the interaction of glutaminase with the mitochondrial inner membrane.

| S-EPMC1162713 | biostudies-other

Purification of phosphate-dependent glutaminase from isolated mitochondria of Ehrlich ascites-tumour cells.

Project description:Phosphate-dependent glutaminase was purified to homogeneity from isolated mitochondria of Ehrlich ascites-tumour cells. The enzyme had an Mr of 135,000 as judged by chromatography on Sephacryl S-300. SDS/polyacrylamide-gel electrophoresis displayed two protein bands, with Mr values of 64,000 and 56,000. Two major immunoreactive peptides of Mr values of 65,000 and 57,000 were found by immunoblot analysis using anti-(rat kidney glutaminase) antibodies. The concentration-dependences for both glutamine and phosphate were sigmoidal, with S0.5 values of 7.6 mM and 48 mM, and Hill coefficients of 1.5 and 1.6, respectively. The glutaminase pH optimum was 9. The activation energy of the enzymic reaction was 58 kJ/mol. The enzyme showed a high specificity towards glutamine. A possible explanation for the different kinetic behaviour found for purified enzyme and for isolated mitochondria [Kovacević (1974) Cancer Res. 34, 3403-3407] should be that a conformational change occurs when the enzyme is extracted from the mitochondrial inner membrane.

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Factors influencing the activity of ornithine aminotransferase in isolated rat liver mitochondria.

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| S-EPMC1164578 | biostudies-other

Factors influencing the drug release from calcium phosphate cements.

Project description:Thanks to their biocompatibility, biodegradability, injectability and self-setting properties, calcium phosphate cements (CPCs) have been the most economical and effective biomaterials of choice for use as bone void fillers. They have also been extensively used as drug delivery carriers owing to their ability to provide for a steady release of various organic molecules aiding the regeneration of defective bone, including primarily antibiotics and growth factors. This review provides a systematic compilation of studies that reported on the controlled release of drugs from CPCs in the last 25 years. The chemical, compositional and microstructural characteristics of these systems through which the control of the release rates and mechanisms could be achieved have been discussed. In doing so, the effects of (i) the chemistry of the matrix, (ii) porosity, (iii) additives, (iv) drug types, (v) drug concentrations, (vi) drug loading methods and (vii) release media have been distinguished and discussed individually. Kinetic specificities of in vivo release of drugs from CPCs have been reviewed, too. Understanding the kinetic and mechanistic correlations between the CPC properties and the drug release is a prerequisite for the design of bone void fillers with drug release profiles precisely tailored to the application area and the clinical picture. The goal of this review has been to shed light on these fundamental correlations.

| S-EPMC8379446 | biostudies-literature

Inhibition by glutamate of phosphate-dependent glutaminase of rat kidney.

Project description:A membrane-associated form of phosphate-dependent glutaminase was derived from sonicated mitochondria and purified essentially free of gamma-glutamyl transpeptidase activity. Increasing concentrations of phosphate cause a sigmoidal activation of the membrane-bound glutaminase. Phosphate also causes a similar effect on the rate of glutaminase inactivation by the two affinity labels, L-2-amino-4-oxo-5-chloropentanoic acid and 6-diazo-5-oxo-L-norleucine, as observed previously for the solubilized and purified enzyme. Therefore the two forms of glutaminase undergo similar phosphate-induced changes in conformation. A sensitive radioactive assay was developed and used to determine the kinetics of glutamate inhibition of the membrane-associated glutaminase. The Km for glutamine decreases from 36 to 4 mM when the phosphate concentration is increased from 5 to 100 mM. Glutamate is a competitive inhibitor with respect to glutamine at both high and low concentrations of phosphate. However, the Ki for glutamate is increased from 5 to 52 mM with increasing phosphate concentration. Therefore glutamine and glutamate interact with the same site on the glutaminase, but the specificity of the site is determined by the available phosphate concentration.

| S-EPMC1153898 | biostudies-other

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

Project description: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.

| S-EPMC1145072 | biostudies-other

Factors influencing the nitrogen-source dependent flucytosine resistance in Cryptococcus species

Project description:Flucytosine (5-FC) is an antifungal drug commonly used for treatment of cryptococcosis and several other systemic mycoses. In fungal species, cytosine permease and cytosine deaminase are known to play major roles in flucytosine resistance by regulating uptake and deamination of 5-FC, respectively. Cryptococcus species have three paralogs of cytosine permease (FCY2, FCY3, and FCY4) and three paralogs of cytosine deaminase (FCY1, FCY5, and FCY6). Like in other fungi, we found Fcy1 and Fcy2 to be the primary cytosine deaminase and permease respectively in C. neoformans H99 (VNI), C. gattii R265 (VGIIa), and WM276 (VGI). However, when different amino acids were used as the sole nitrogen source, Fcy3 and Fcy6 functioned as the secondary cytosine permease and deaminase respectively in C. gattii. Transcriptome analysis using RNA-seq under three different nitrogen sources (NH4, Asn, and Pro) revealed that these permease and deaminase genes as well as two GATA family transcription factor genes, GAT1 and CIR1, were differentially expressed in WM276. In addition, deletion studies of GAT1 and CIR1 demonstrated that the expression of each permease and deaminase genes was under the regulation of GAT1 and CIR1 individually. Furthermore, the expression levels of FCY3 and FCY6 regulated by GAT1 and CIR1 contributed to the 5-FC susceptibility in fcy2Δ or fcy1Δ background under different amino acid conditions. This study offers an insight into the mechanism of 5-FC resistance in C. gattii which is orchestrated by cytosine permease and deaminase genes, and two GATA family transcription factor genes, GAT1 and CIR1, under diverse nitrogen conditions.

2023-01-11 | GSE215311 | GEO

Intracellular localization and properties of phosphate-dependent glutaminase in rat mesenteric lymph nodes.

Project description:Phosphate-dependent glutaminase was present at approximately similar activities in lymph nodes from mammals other than rat, and in thymus, spleen, Peyer's patches and bone marrow of the rat. This suggests that glutamine is important in all lymphoid tissues. Phosphate-dependent glutaminase activity was shown to be present primarily in the mitochondria of rat mesenteric lymph nodes, and most of the activity could be released by detergents. The properties of the enzyme in mitochondrial extracts were investigated. The pH optimum was 8.6 and the Km for glutamine was 2.0 mM. The enzyme was activated by phosphate, other phosphorylated compounds including phosphoenolpyruvate, and also leucine: 50% activation occurred at 5, 0.2 and 0.6 mM for phosphate, phosphoenolpyruvate and leucine respectively. The enzyme was inhibited by glutamate, 2-oxoglutarate, citrate and ammonia, and by N-ethylmaleimide and diazo-5-oxo-L-norleucine; 50% inhibition was observed at 0.7 and 0.1 mM for glutamate and 2-oxoglutarate respectively. Some of these properties may be important in the control of the enzyme activity in vivo.

| S-EPMC1153208 | biostudies-other

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