Disease relevance of GLS

• Thus in humans, alternative splicing of the initial transcript could produce two GA mRNAs, only one of which may be increased during acidosis [1].
• Limited proteolysis of Pseudomonas glutaminase by porcine trypsin [2].

High impact information on GLS

• Desenzitation to inhibition by mersalyl and N-ethylmaleimide occurred when the assay was performed under optimal conditions for phosphate activated glutaminase (i.e. in the presence of 150 mM phosphate, 20 mM glutamine and at pH 8.6) [3].
• Phosphate-activated glutaminase in intact pig renal mitochondria was inhibited 50-70% by the sulfhydryl reagents mersalyl and N-ethylmaleimide (0.3-1.0 mM), when assayed at pH 7.4 in the presence of no or low phosphate (10 mM) and glutamine (2 mM) [3].
• The results suggest that phosphate-activated glutaminase has a functionally predominant external localization in the inner mitochondrial membrane [3].
• Furthermore, both calcium (which activates glutamine hydrolysis), as well as alanine (which has no effect on the hydrolytic rate), inhibited glutamine transport into the mitochondria, indicating that transport of glutamine is not rate-limiting for the glutaminase reaction [3].
• Exposure of cells to either PGF2 alpha or TPA completely inhibited the low pH-induced increases in (15N)ammonia formation from incubations with 5-15N, reflecting reduced flux through the mitochondrial phosphate-dependent glutaminase, and from (2-15N)glutamine, reflecting reduced flux through the mitochondrial glutamate dehydrogenase pathway [4].

Chemical compound and disease context of GLS

• Pulse-chase studies with 14C-glutamine as well as studies with various metabolic inhibitors of the ammoniagenic pathways suggest that glutamine in LLC-PK1 cells is metabolized via mitochondrial pathway and that intramitochondrial phosphate-dependent glutaminase pathway plays a predominant role in the regulation of ammoniagenesis to acute acidosis [5].
• Thus reduced cellular glutamate appears to coordinate activation of intracellular glutaminase to the apical membrane exchanger, consistent with the functioning kidney response to metabolic acidosis [6].

Biological context of GLS

• However, insertion of short segments of GA mRNA containing the direct repeat or a single eight-base AU sequence was sufficient to impart a fivefold pH-responsive stabilization to the chimeric mRNA [7].
• It is concluded that aspartate aminotransferase activity appears to be especially concerned with cochlear energy metabolism, while glutaminase activity may function in transmitter metabolism in the guinea pig cochlea [8].
• Although GA activation occurs as the result of the fall in cellular L-glutamate, PP did not increase; in fact, it slightly decreased as evidenced by an increased electrical resistance (from 180 +/- 12 to 210 +/- 10 omega x cm2, P < 0.02) and reduction in L-[(14)C]glucose permeability (2.72 +/- 0.75 to 2.28 +/- 0.37%, P = 0.10) [9].

Anatomical context of GLS

• Two pools of phosphate-activated glutaminase (PAG) were separated from pig and rat renal mitochondria [10].
• Thus the enzymatically active PAG is assumed to be localized on the outer face of the inner mitochondrial membrane [10].
• The activity of this pool of PAG appears to be regulated by compounds in the cytosol, of which glutamate may be most important [10].
• LLC-PK1-FBPase+ cells, a pH-responsive porcine kidney cell line, express four distinct GA mRNAs [1].
• Given this complexity, a careful assessment of GA mRNA species, of basal expression, and of growth conditions are essential for a meaningful analysis of GA mRNA levels in cultured cells [11].

Associations of GLS with chemical compounds

• In contrast, decreases in the activities of phosphate-dependent glutaminase, ornithine aminotransferase, ornithine carbamoyltransferase and carbamoyl-phosphate synthase were observed as the age of the pigs increased [12].
• The fatty acyl-CoA derivatives affect glutaminase similarly to Bromothymol Blue, but differently from acetyl-CoA, which activates the enzyme only at very low phosphate or citrate concentrations [13].
• Olfactory bulb removal and consequential degeneration of the lateral olfactory tract led to a decrease in the levels of glutaminase and malate dehydrogenase in the ipsilateral olfactory cortex [14].
• Tetraphenylboron - a potent activator of kidney mitochondrial glutaminase [15].
• The activity of serine hydroxymethyl transferase, which converts serine into glycine, was similar in white and gray matter (11-18pmol/(mgtissue)min), whereas the white matter activity of phosphate-activated glutaminase, which converts glutamine into glutamate, was approximately 100pmol/(mgtissue)min, or approximately 34% of gray matter activity [16].

Other interactions of GLS

• Placental tissue was analyzed for amino acid concentrations, BCAA transport, BCAA degradation, and glutamine synthesis as well as the activities of related enzymes (including BCAA transaminase, branched-chain alpha-ketoacid dehydrogenase, glutamine synthetase, glutamate-pyruvate transaminase, and glutaminase) [17].
• The activities of carbamoylphosphate synthase-I (-45%), argininosuccinate synthase (-38%), argininosuccinate lyase (-23%), arginase (-27%), and glutaminase (-18%), but not of ornithine carbamoyltransferase, ornithine aminotransferase, or glutamate dehydrogenase were reduced in liver of ST-treated pigs [18].

Analytical, diagnostic and therapeutic context of GLS

• PCR cloning and sequencing established that the latter GA mRNA is the homolog of the human GAC mRNA [1].
• The perfusion of enzyme glutamine synthetase elevated the CAP threshold by 50 dB, while glutaminase had little effect [19].

References