Brain glutamine synthesis requires neuronal-born aspartate as amino donor for glial glutamate formation

The glutamate–glutamine cycle faces a drain of glutamate by oxidation, which is balanced by the anaplerotic synthesis of glutamate and glutamine in astrocytes. De novo synthesis of glutamate by astrocytes requires an amino group whose origin is unknown. The deficiency in Aralar/AGC1, the main mitochondrial carrier for aspartate–glutamate expressed in brain, results in a drastic fall in brain glutamine production but a modest decrease in brain glutamate levels, which is not due to decreases in neuronal or synaptosomal glutamate content. In vivo ¹³C nuclear magnetic resonance labeling with ¹³C₂acetate or (1-¹³C) glucose showed that the drop in brain glutamine is due to a failure in glial glutamate synthesis. Aralar deficiency induces a decrease in aspartate content, an increase in lactate production, and lactate-to-pyruvate ratio in cultured neurons but not in cultured astrocytes, indicating that Aralar is only functional in neurons. We find that aspartate, but not other amino acids, increases glutamate synthesis in both control and aralar-deficient astrocytes, mainly by serving as amino donor. These findings suggest the existence of a neuron-to-astrocyte aspartate transcellular pathway required for astrocyte glutamate synthesis and subsequent glutamine formation. This pathway may provide a mechanism to transfer neuronal-born redox equivalents to mitochondria in astrocytes.     

Systems biology of cyanobacterial secondary metabolite production and its role in drug discovery

Background: Cyanobacteria continue to be an important source of compounds that show unprecedented biological activities of pharmaceutical interest. Cyanobacterial metabolites show an interesting and exciting range of biological activities ranging from antimicrobial and immunosuppressant to anticancer and anti-HIV. Objective: This review explores the possibilities of applying systems biology approaches for harnessing these compounds as drug leads, primarily produced through large multimodular non-ribosomal peptide synthetase (NRPS), polyketide synthase (PKS) and mixed NRPS–PKS enzymatic systems. Methods: A brief survey of the strategies for in silico analysis for drug target identification using genomic and high-throughput proteomics data, virtual screening and receptor–ligand docking based approaches are also discussed. Conclusion: We conclude with an outlook on how the field will evolve, especially in partnership with the new engineering-based, more endpoint exploitative paradigm of synthetic biology.     

酰基激酶和酰基CoA合成酶对螺旋霉素合成的影响

螺旋霉素链霉菌生物合成螺旋霉素的过程受许多酶的调控作用，酰基激酶和酰基CoA合成酶是螺旋霉素内酯环合成的重要酶，实验测定了它们的酶活趋势和酶的影响因子，结果表明，酰基激酶和酰基CoA合成酶都有两个活力峰，前者活性集中在发酵中前期，后者活性集中在发酵中后期，实验发现Co2 ,Mn2 对酰基激酶和酰基CoA合成酶有较强的激活作用，Cu2 对酰基激酶有抑制作用，但对酰基CoA合成酶有很强的激活作用，在发酵中期向摇瓶中补加二阶阳离子比在发酵初期加入有更明显的激活作用，平均效价最高提高了31％。     

神经原性膀胱NOS的免疫组化研究

目的研究一氧化氮合成酶(NOS)在神经原性膀胱(NB)的两种类型中的分布。方法应用免疫组化技术对23例患儿进行检测。将18例NB患儿按尿流动力学检查结果分为逼尿肌反射亢进型(11例)和逼尿肌反射低下型(7例)，将非NB患儿5例按照有无尿道出口梗阻引起的膀胱静息压升高分为膀胱静息压升高组(2例)和正常组(3例)。结果NOS含量在逼尿肌反射亢进型较反射低下型有显著增高。膀胱内压升高组NOs含量较正常组明显升高。结论NOS参与膀胱功能的调节和神经原性膀胱的病生理变化。     

Metabolism of [U‐13C]glucose in human brain tumors in vivo

Glioblastomas and brain metastases demonstrate avid uptake of 2‐[¹⁸F]fluoro‐2‐deoxyglucose by positron emission tomography and display perturbations of intracellular metabolite pools by ¹H MRS. These observations suggest that metabolic reprogramming contributes to brain tumor growth in vivo. The Warburg effect, excess metabolism of glucose to lactate in the presence of oxygen, is a hallmark of cancer cells in culture. 2‐[¹⁸F]Fluoro‐2‐deoxyglucose‐positive tumors are assumed to metabolize glucose in a similar manner, with high rates of lactate formation relative to mitochondrial glucose oxidation, but few studies have specifically examined the metabolic fates of glucose in vivo. In particular, the capacity of human brain cancers to oxidize glucose in the tricarboxylic acid cycle is unknown. Here, we studied the metabolism of human brain tumors in situ. [U‐¹³ C]Glucose (uniformly labeled glucose, i.e. d ‐glucose labeled with ¹³ C in all six carbons) was infused during surgical resection, and tumor samples were subsequently subjected to ¹³C NMR spectroscopy. The analysis of tumor metabolites revealed lactate production, as expected. We also determined that pyruvate dehydrogenase, turnover of the tricarboxylic acid cycle, anaplerosis and de novo glutamine and glycine synthesis contributed significantly to the ultimate disposition of glucose carbon. Surprisingly, less than 50% of the acetyl‐coenzyme A pool was derived from blood‐borne glucose, suggesting that additional substrates contribute to tumor bioenergetics. This study illustrates a convenient approach that capitalizes on the high information content of ¹³C NMR spectroscopy and enables the analysis of intermediary metabolism in diverse cancers growing in their native microenvironment. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of glutamine dependency in non-small cell lung cancer: GLS1 splice variant GAC is essential for cancer cell growth

One of the hallmarks of cancer is metabolic deregulation. Many tumors display increased glucose uptake and breakdown through the process of aerobic glycolysis, also known as the Warburg effect. Less studied in cancer development and progression is the importance of the glutamine (Gln) pathway, which provides cells with a variety of essential products to sustain cell proliferation, such as ATP and macromolecules for biosynthesis. To this end Gln dependency was assessed in a panel of non-small cell lung cancer lines (NSCLC). Gln was found to be essential for the growth of cells with high rates of glutaminolysis, and after exploring multiple genes in the Gln pathway, GLS1 was found to be the key enzyme associated with this dependence. This dependence was confirmed by observing the rescue of decreased growth by exogenous addition of downstream metabolites of glutaminolysis. Expression of the GLS1 splice variant KGA was found to be decreased in tumors compared with normal lung tissue. Transient knock down of GLS1 splice variants indicated that loss of GAC had the most detrimental effect on cancer cell growth. In conclusion, NSCLC cell lines depend on Gln for glutaminolysis to a varying degree, in which the GLS1 splice variant GAC plays an essential role and is a potential target for cancer metabolism-directed therapy.     

Identification of a methicillin-resistant Staphylococcus aureus inhibitory compound isolated from Serratia marcescens

In this study, we identified an antimicrobial compound produced by the Gram-negative bacterium Serratia marcescens. Colonies of S. marcescens inhibited the growth of nine different methicillin-resistant Staphylococcus aureus (MRSA) isolates and several other tested Gram-positive bacterial species, but not Gram-negative bacteria. Genetic analysis revealed the requirement for the swrW gene which codes for a non-ribosomal peptide synthetase that generates the cyclodepsipeptide antibiotic serratamolide, also known as serrawettin W1. This is the first report describing the anti-MRSA properties of serratamolide.     

Glycosidic intermediates identified in 1H MR spectra of intact tumour cells may contribute to the clarification of aspects of glycosylation pathways

The glycosylation process, through the addition of carbohydrates, is a major post‐translational modification of proteins and glycolipids. Proteins may be glycosylated in either the secretory pathway leading to N‐linked or O‐linked glycoproteins or as nucleocytoplasmic glycosylation that targets only single proteins involving a single β‐linked N‐acetylglucosamine. In both cases, the key precursors are the uridine diphospho‐N‐acetylhexosamines synthesised by the hexosamine biosynthetic pathway. Furthermore, uridine diphospho‐N‐acetylglucosamine participates in the biosynthesis of sialic acid. In this work, we propose MRS for the detection of uridine diphospho‐N‐acetylhexosamines visible in high‐resolution MR spectra of intact cells from different human tumours. Signals from the nucleotide and amino sugar moieties, including amide signals observed for the first time in whole cells, are assigned, also taking advantage of spectral changes that follow cell treatment with ammonium chloride. Finally, parallel changes in uridine diphospho‐N‐acetylhexosamines and glutamine pools, observed after pH changes induced by ammonium chloride in the different tumour cell lines, may provide more details on the glycosylation processes. Copyright © 2010 John Wiley & Sons, Ltd.