Wyniki wyszukiwania - Biblioteka Nauki

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Pochodne fosforylowanych cukrów jako inhibitory syntazy GLcN-6-P

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Melcer A.

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2010

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tom [Z] 64, 9-10

771-786

EN

A reaction catalyzed by glucosamine-6-phosphate synthase (L-glutamine: D-fructose-phosphate amidotransferase, Glms) is the first step committed to the amino-sugar biosynthetic pathway of all living organisms [1]. This is in particular the only endogeneous access to hexosamines which are absolutely required in the edification of microbial cell walls. Glucosamine-6-phosphate synthase was proposed as a target for antifungal chemotherapy and a search for its selective inhibitors as potential antifungals has been continued [2]. This enzyme catalyzes two coupled enzymatic reactions. The first is the hydrolysis of glutamine to yield glutamate and nascent ammonia, which is transferred to Fru-6-P. The second reaction is the isomerization of Fru-6-P to an aldose, corresponding to Heyns rearrangement (3, 4). Like other amidotransferases, GlmS is organized into two domains: the NH2-terminal glutamine amidotransferase domain, which catalyzes the hydrolysis of glutamine, and the COOH-terminal synthase domain, which catalyzes the isomerization (5-8). The glutamine hydrolysis reaction has been studied extensively and utilises the NH2-terminal cysteine thiol, which forms a g-glutamyl thioester intermediate during the reaction. This catalytic role was confirmed by conversion of the NH2-terminal cysteine to alanine using site-directed mutagenesis which abolished enzymatic activity [2]. The already known specific inhibitors of GlcN-6-P synthase belong to two different structural groups: L-glutamine mimics and analogues of the putative transition state intermediates. In general, glutamine amidotransferases are inactivated by glutamine afinity analogues such as 6-diazo-5-oxo-L-norleucine and 6-chloro-5-oxo-L-norleucine (chloroketone), which alkylate the essential cysteine residue (5, 6, 9). Indeed, many of the active site-directed irreversible inactivators developed for GlmS contain an electrophilic function at the ă -position of glutamate and react irreversibly with the NH2-terminal cysteine residue. More recently, attempts to develop carbohydrate-based inhibitors have been made with the hope of developing higher specificity (10-13). The second group of compounds comprises derivatives of phosphorylated aminosugars, including: 2-amino-2-deoxy-D-glucitol-6-phosphate (ADGP), arabinose-5-phosphate oxime and 5-methylenephosphono-D-arabinohydroximolactone, as the most powerful GlcN-6-P synthase inhibitors [11-15]. These compounds exhibit a very poor, if any, antifungal activity. This paper describes the inhibition of GlmS by several analogues of the cis-enolamine intermediate in an attempt to probe the structural requirements for potent inhibition of this enzyme. The energetic contribution of the 2-amino group to binding of the product and the cis-enolamine intermediate is determined.

2

Analogi glutaminy jako inhibitory syntazy GLcN-6-P

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Melcer A.

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2010

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tom [Z] 64, 11-12

995-1012

EN

Glucosamine-6-P (GlcN-6-P) synthase catalyzes the first committed step in chitin biosynthesis pathway, that is, transformation of D-fructose-6-phosphate (Fru-6-P) to D-glucosamine-6-phosphate [1]. Although the enzyme is also present in mammalian systems, substantial difference in physiological consequences of GlcN-6-P synthase inhibition in fungi and in mammals, constitute a firm molecular basis for the selective toxicity of specific enzyme inhibitors. The enzyme was proposed as a target for antifungal chemotherapy and a search for its selective inhibitors as potential antifungals has been continued. So far, two main groups of such compounds were identified: L-glutamine analogs and mimics of a putative cis-enolamine transition state intermediate but none of them demonstrated high antifungal activity, due to the inefficient uptake by the fungal cells. Among a number of known glutamine analogues some are selective inhibitors of GlcN-6-P synthase, not interacting with other enzymes utilising L-glutamine as substrate. One of them, N3-(4-methoxyfumaroyl)- l-2,3-diaminopropanoic acid (FMDP), gave rise to oligopeptidic compounds demonstrating remarkable antifungal activity [2]. Incorporation of FMDP into peptide structure allowed effective internalisation of the enzyme inhibitor by the way of peptide permeases, but on the other hand was a reason of substantial specific resistance, since peptides permeases are not essential for fungal cells [3, 4]. The second group of compounds comprises derivatives of phosphorylated aminosugars, including: 2-amino-2-deoxy-D-glucitol-6-phosphate (ADGP), arabinose-5- -phosphate oxime and 5-methylenephosphono-D-arabinohydroximolactone, as the most powerful GlcN-6-P synthase inhibitors [5–7]. These compounds exhibit very poor, if any, antifungal activity. This article provides a comprehensive overview of the present knowledge about inhibitors of glucosamine-6-phosphate and their synthesis.

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Ocena ekonomiczna recyklingu krzemowych ogniw fotowoltaicznych, realizowanego w skali laboratoryjnej

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Klugmann-Radziemska E. , Ostrowski P. , Melcer A.

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2010

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tom R. 18, nr 6

310-318

PL

W ostatnich latach nastąpił niespotykany jak dotąd wzrost ilości zainstalowanych systemów fotowoltaicznych (PV), które stanowić mogą przyjazną dla środowiska alternatywę dla konwencjonalnych źródeł zasilania. Ze względu na ich wieloletnią gwarancję, udzielaną przez producentów, moduły PV stają się odpadem po 25-letnim okresie eksploatacji. Najcenniejszym materiałem, jaki można odzyskać w procesie recyklingu zużytych lub uszkodzonych modułów jest krzem. Opracowano technologię odzyskiwania płytek krzemowych w procesie, składającym się z następujących etapów: separacja ogniw metodą termiczną, usuwanie warstwy antyrefleksyjnej i metalizacji przedniej oraz tylnej, usuwanie złącza p-n metodą chemiczną. Zoptymalizowano skład mieszanin trawiących z punktu widzenia wydajności i czasu trwania procesu. W artykule przedstawiono analizę korzyści ekonomicznych realizacji opracowanej metody recyklingu ogniw PV z krystalicznego krzemu.

EN

In recent years, photovoltaic power generation systems have been gaining unprecedented attention as an environmentally beneficial method for solving the energy problem. From the economic point of view pure silicon, which can be recovered from spent cells, is the most important material owing to its cost and limited supply. The article presents an economical analysis of chemical method for recycling spent or damaged modules and cells. The recycling of PV cells consists of two main steps: the separation of cells and their refinement. Cells are first separated thermally or chemically; the separated cells are then refined. During this process the antireflection, metal coating and p-n junction layers are re-moved in order to recover the silicon base, ready for its next use. This refinement step was performed using an optimised chemical method. The silicon wafers were used for producing new silicon solar cells, which were then examined and characterized with internal spectral response and current-volt-age characteristics.

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Nowe możliwości energooszczędnego budownictwa pasywnego. Zastosowanie termoizolacyjnych materiałów zmiennofazowych

51%

Lewandowski W. M. , Lewandowska-Iwaniak W. , Melcer A.

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2011

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tom Nr 4

34-37

PL

W artykule opisano materiały budowlane zawierające substancje podlegające przemianom fazowym (PCM - Phase Change Material). Stała temperatura przemiany fazowej pozwala stabilizować temperaturę nie tylko poszczególnych pomieszczeń, ale również całych budynków, w których materiały te zostały zastosowane.